Committee on Publication Barton W. Evermann Chairman and Editor C. Hart Merriam Henry Gannett A. D. Hopkins Arthur L. Day PROCEEDINGS OF THE Washington Academy of Sciences Vol. VIII 1906 WASHINGTON May, 1906-MARCH, 1907 AFFILIATED SOCIETIES. Anthropological Society of Washington. Biological Society of Washington. Botanical Society of Washington. Chemical Society of Washington. Columbia Historical Society. Entomological Society of Washington. Geological Society of Washington. Medical Society of the District of Columbia. National Geographic Society. Philosophical Society of Washington. Society of American Foresters. Washington Society of the Archaeological Institute of America. Washington Society of Engineers. 3L1 L PRE98 OF The New Eh* Printing Company Lancaster, Pa. CONTENTS. PAGE Mexican, Central American, and Cuban Cambari ; by A. E. Ortmann i The Geodetic Evidence of Isostasy ; by John F. Hayford . . 25 Distribution of the Lymphatics in the Head, and in the Dorsal, Pectoral and Ventral Fins of Scorpaenichthys marmoratus ; by Wm. F. Allen 41 Evidences bearing on Tooth-cusp Development; by James Williams Gidley 91 New Starfishes from the Pacific Coast of North America; by Walter K. Fisher in Notes on Japanese Hepaticae ; by Alexander W. Evans . . 141 A Study of Rhus glabra; by Edward L. Greene . . . 167 Aspects of Kinetic Evolution ; by 0. F. Cook . . . . 197 Age of the Pre-volcanic Auriferous Gravels in California ; by J. S. Diller 405 Aerial Locomotion ; by Alexander Graham Bell . . . 407 On a Collection of Fishes from Buenos Aires; by Carl H. Eigen- mann ........... 449 Histology and Development of the divided Eyes of certain Insects ; by George Daniel Shaf er 46 1 Index ........... 487 ILLUSTRATIONS FACING PAGE I. Lymphatic System in Scorficenichthys marmoratus 90 II. Portion of same continued 90 III . Portion of same continued 90 IV. Cheek Teeth of Living Insectivores and Bats 108 V. Teeth of Mesozoic Mammals no VI. Japanese Hepaticae 162 VII. Japanese Hepaticae 164 VIII. Japanese Hepaticae .. 166 IX. LilienthaFs and Chanute's Gliding Machines 448 X. Langley's Aerodrome No. 5 in flight May 6, 1896 448 XL The Accident to Langley's Aerodrome 448 XII. The Wright Brothers' Gliding Machine 448 XIII. Bell Tetrahedral Kites 448 XIV. The Bell Tetrahedral Kite, "Frost King" 44S XV. The Frost King flying in a Ten-mile Breeze 448 XVI. The Bell Tetrahedral Kite " Siamese Twins," front view. 448 XVII. The Bell Tetrahedral Kite " Siamese Twins," rear view. 448 XVIII. A Floating Kite, adapted to be towed out of the water .. 448 XIX. The Dirigible Airships " Patrie " and " Villede Paris".. 448 XX. Count von Zeppelin's Airship 448 XXI. Placostomus lafilatce Eigenmann 458 XXII. Loricaria vetula Cuvier & Valenciennes 45 S XXIII. Po?nolobus melanosto?nus, Geophagus australe and Batrachops scottii 45 8 XXIV. Divided Eyes of Certain Insects 480 XXV. Divided Eyes of Certain Insects 482 XXVI. Divided Eyes of Certain Insects 4S4 XXVII. Microphotographs of Insect Eyes 4S6 WASHINGTON ACADEMY OF SCIENCES OFFICERS ELECTED JANUARY 17, 1907 Presiden t Charles D. Walcott Vice-Presidents From the Anthropological Society W. H. Holmes Archceological Society John W. Foster Biological Society Leonhard Stejneger Botanical Society David White Chemical Society F. W. Clarke Columbia Historical Society A. R. Spofford Entomological Society A. D. Hopkins Geological Society C. Willard Hayes Medical Society D . Kerfoot Shute National Geographic Society Willis L. Moore Philosophical Society John F. Hayford Society of Engineers F. H. Newell Society of American Foresters Gifford Pinchot Secretary Frank Baker Class 0/1908 Barton W. Evermann L. O. Howard O. H. Tittmann Treasarer Bernard R. Green Managers Class 0/1909 Class of 1910 L. A. Bauer Frederick V. Coville C. F. Marvin J. S. Diller C. HartMerriam Geo. M. Kober Standing Committees for 1907 Committee on Meetings L. A. Bauer, Chairman C. W. Hayes J. D. Morgan F. V. Coville E. B. Rosa Committee on Publication Barton W. Evekmann, Chairman C. Hart Merriam Hfary Gannett A. D. Hopkins Arthur L. Day Vlll WASHINGTON ACADEMY OF SCIENCES Committee on Finance Tiieo. N. Gill, Chairman Bernard R. Green E. M. Gallaudet L. O. Howard Geo. O. Smith Committee on Rules O. H. Tittmann, Chairman A. K. Fisher J. H. Gore Committee on Membership F. V. Coville, Chair 7na?t Willis L. Moore C. K. Wead Lyman J. Briggs Geo. W. Littlehales D. K. Shute Committee on Building Geo. M. Kober, Chairman Lyman J. Briggs Arnold Hague Geo. T. Vaughan David White Committee on Functions C. F. Marvin, Chairman F. W. Clarke R. A. Harris Committee on Affiliation F. W. Clarke, Chairman Whitman Cross J. F. Hayford C L. Marl att E. W. Nelson NINTH ANNUAL REPORT OF THE SECRETARY, 1906. To the Washington Academy of Sciences : Mr. President and Members of the Academy : During the period from January iS, 1906, to January 17, 1907, the Academy has held the following meetings : January iS, 1906 — Annual meeting for the election of officers, etc. February 6, 1906 — Meeting to hear an address by Prof. Harry Fielding Reid on " The Various Methods of Estimating the Age of the Earth." This was discussed by Prof. Henry F. Osborn, Prof. Simon Newcomb and Mr. Bailey Willis. February 23, 1906 — Meeting to hear a paper on u Old Age, Its Nature and Cause," by Prof. Chas. Sedgwick Minot. Discussed by Prof. A. F. A. King, Marshall A. Price and Dr. Harvey W. Wiley. February 27, 1906 — Meeting to hear the annual address of the President of the Anthropological Society, Dr. Geo. M. Kober, on " The Health of the City of Washington." April 14, 1906 — Meeting to hear a paper by Mr. John F. Hay- ford, on " The Recent Geodetic Evidence of Isostasy and its bearing upon the greater Geologic Problems." Introduced by Mr. O. H. Titt- mann and dircussed by Major C. E. Dutton, Dr. C. Willard Hayes and others. May 17, 1906 — Meeting to hear an address by Prof. Francis Gano Benedict on "The Respiration Calorimeter and the Factors of Human Nutrition." Discussed by Dr. J. B. Nichols, Dr. E. B. Rosa, and Dr. C. F. Langworthy. November 27, 1906 — Meeting to hear an address by Prof. Chas. Hubbard Judd on " Visual Perception." Discussed by Prof. G. M. Stratton. December 13, 1906 — Meeting to hear an address by Dr. Alexander Graham Bell on " Aerial Locomotion." Discussed by Mr. C. F. Manly and Prof. A. F. Zahm. At the meeting of November 27, amendments to the By-Laws were adopted providing for a class of life members. The Board of Managers has held eight meetings for the transaction of business. X WASHINGTON ACADEMY OF SCIENCES Mr. Alexander Graham Bell having resigned the office of Vice- President, the National Geographic Society nominated in his place Mr. Willis L. Moore, who was duly elected by the Board. Delegates were sent to represent the Academy at the celebration of the 200th anniversary of Franklin's birth held by the American Philo- sophical Society, April 17-20, 1906. A Committee of Arrangements has been appointed to prepare for the reception of the International Zoological Congress which is to visit Washington in August, 1907. At the time of the passage by Congress of the bill establishing a Board of Education in the District of Columbia the Managers sent to each Justice of the Supreme Court of the District of Columbia a reso- lution recommending the appointment on the Board of one or more members of recognized ability and attainment in some of the natural sciences and who are thoroughly familiar with modern methods of scientific teaching. Dr. Barton W. Evermann was subsequently appointed. Vol. VII of the Proceedings has been completed and issued during the year and Vol. VIII is well advanced toward completion. A new catalogue of the members of the Academy and Affiliated Societies has been projected and is now in course of preparation. Application having been made by the Washingten Society of Engi- neers for admission to the group of Affiliated Societies it was favor- ably considered by the Board. A vote of the Academy is now being taken by correspondence, as provided by Art. VI, Sec. 2, of the By- Laws. The Academy has suffered the following losses by death during the year : H. G. Ogden died February 26, 1906. S. P. Langley died February 27, 1906. The statistics of membership at this date are as follows : Patrons : At date of last report S Elected during the year o S Honorary Members : At date of last report o Elected during the year 1 1 Life Members : At date of last report o Elected during the year 1 1 NINTH ANNUAL REPORT OF THE TREASURER XI Resident Members : At date of last report 167 Elected and qualified during the year 10 Transferred from non-resident list 1 178 Deceased 2 Resigned 4 Transferred to honorary list 1 7 171 Non-resident Members : At date of last report 173 Elected and qualified during the year 13 186 Resigned 9 Transferred to life list 1 Transferred to resident list 1 11 175 356 Counted twice 1 Total membership January 17, 1907 355 Respectfully submitted, Frank Baker, Secretary. January 17, 1907. NINTH ANNUAL REPORT OF THE TREASURER, 1906. To the Washington Academy of Sciences : The Treasurer has the honor to submit the following annual report of receipts, disbursements, and funds in his hands for the year from January 1, 1906, to December 31, 1906, when the account was closed and balanced : The receipts during the year have been as follows : Dues of resident members, 1903 $ 5.00 Dues of resident members, 1904 10.00 Dues of resident members, 190^ 65.00 Dues of resident members, 1906 710.00 $ 790.00 Dues of non-resident members, 1904 5-oo Dues of non-resident-members, 1905 30.00 Dues of non-resident members, 1906 775.20 Dues of non-resident members, 1907 ^.00 S15.20 xii WASHINGTON ACADEMY OF SCIENCES Sales of Publications and refunds from authors for re- prints, etc 164.56 Interest on bank deposits and investments 622.97 Cash returned by Committee on Meetings, balance not used expenses meetings of November 27 and December 13, 1906 9. 84 Total receipts $2,402.57 The amounts and objects of the expenditures were as follows : Paid on account of expenses incurred in previous year, 1905 : Secretary's office $ 6.40 Meetings I7'7° Publishing Vol. VII of Proceedings 441.00 Editor's office, 1905 500.00 965.10 Paid on account of expenses of the past year, 1906 : Secretary's office $ 33.71 Treasurer's office 101.39 Meetings 291.09 Publishing Vol. VIII of Proceedings 632.07 Greeting to American Philosophical Society of Philadelphia 15.00 $1,073.26 Total disbursements $2,038.36 Statement of Account. Balance from last annual statement $ 810.^3 Receipts duringthe year 2,402.57 To be accounted for $3,213.10 Disbursements during the year 2,038.36 Cash balance on hand $1,174.74 Of this balance $195.09 belongs to the permanent fund, leaving $979.65 available for general expenses. These funds are on deposit with the American Security and Trust Company, drawing 2 per cent, interest. The only outstanding bills within the knowledge of the Treasurer are : Editor's office, 1906 $500.00 Expenses of meetings 8.75 Expenses of Secretary's office 27.00 NINTH ANNUAL REPORT OF THE TREASURER Mil and the completion and binding of Vol. VIII of the Proceedings, which, it is understood, will not exceed the balance of funds on hand. Dues remain unpaid as follows : For 1902, $ 10 *903i x5 i9°4. 35 1905, 60 1906, 250 $37o The investments are the same as stated in the last annual report, namely : Cash on hand belonging to permanent fund $ 195.09 809 shares stock of Washington Sanitary Improvement Co. 8,090.00 1 share stock of Colonial Fire Insurance Co 100.00 2 shares stock Scheutzen Park Land & Building Associa- tion, par value $100, actual value doubtful, say $44.00 SS.00 2 first trust notes of Laura R. Green, 3 years, 5 per cent. interest, for $2,000, and $1,500 3,500.00 1 first trust note of Aurelius R. Shands, 3 years, 4^ per cent, interest 444.44 $12,417.53 The two notes of Laura R. Green are deposited with Thos. J. Fisher & Co., Washington, D. C, for collection of interest, and the remainder of the investments are in the Academy's safe deposit box at the Union Trust Company. Respectfully submitted, Bernard R. Green, Treasurer. January 5, 1907. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 1-24. May 3, 1906. MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI. By A. E. Ortmann, Carnegie Museum, Pittsburg, Pa. The larger part of the material, upon which the following notes are based, was loaned to the writer by the Museum of Natural History of Paris through the kindness of Professor E. L. Bouvier, for which I wish to express my most sincere thanks. I am also under obligations to the Academy of Natural Sciences of Philadelphia, where I was granted the privilege of examin- ing the crawfish-collections ; some of this material has also been used for the following notes. I. Subgenus PARACAMBARUS, new subgenus. Paracambarus, new subgenus of Potamobiidas ( Cambarus ■paradoxus ) . Sexual organs of male with the two parts in close apposition to their tips ; in the male of the first form, both tips are shortly pointed and horny ; in addition there is, on the posterior margin of Ire inner part, at a short distance from the tip, a long and strong, horny spine. Anterior margin of sexual organs with- out shoulder. Male with hooks on the ischiopodite of fourth perciopods only. Female with a spin form process on the sternum between the fifth perciopods. The presence of hooks only on the fourth pereiopods of the male, and the peculiar spine of the sternum of the female dis- Proc. Wash. Acad. Sci., May, 1906. 1 2 ORTMANN tinguish this subgenus at once from all other Cambari} The male copulatory organs are also different from those of any- other species of the genus, but they approach, to a certain de- gree, those of the subgenera Procambarus and Cambarus. This is the sixth subgenus distinguished by the writer within the genus Cambartis.2 It may be well to point out here the most important characters of these six subgenera by arranging them into a key. KEY FOR THE SUBGENERA OF CAMBARUS. a. Outer and inner part of male sexual organs in close apposition up to their tips ; tips in the male of the first form horny or soft, with accessory horny spines. b. Both tips of male organs horny; inner part with a strong acces- sory spine on posterior margin. Female with a spine on sternum between fifth pereiopods. Male with hooks on ischi- opodite of fourth pereiopods Paracantbarus. bb. Both tips of male organs soft, with accessory horny spines on one of them. Female without spine on sternum between fifth pereiopods. Male with hooks on ischiopodite of third, or of third and fourth pereiopods. c. Male organs with a small accessory spine, belonging to the inner part ; anterior margin with a shoulder near the tips ; male with hooks on third pereiopods Procambarus. cc. Male organs with one to three horny accessory spines (often tuberculiform or plate-like), belonging to the outer part; shoulder generally absent, if present, remote from the tips ; male with hooks on third, or on third and fourth pereiopods. Cambarus. aa. Outer and inner part of male sexual organs distinctly separated for a more or less considerable distance at the tips; outer part, in the male of the first form, entirely transformed into a horny spine, rarely with a soft secondary spine. d. Outer part of male organs consisting of two rather long spines, one horny, the other soft, bristle-like ; male with hooks on second and third pereiopods Cambarellus. dd. Outer part of male organs formed by one single horny spine; 1 Except Cambarus montezuma; (subgenus Cambarellus). 2 See Proc. Amer. Philos. Soc, XLIV, 1905, 96 and 97, and Ann. Carnegie Mus., III. 1905, 437. MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 3 male generally with hooks on third pereiopods, rarely on third and fourth pereiopods. e. The two parts of the male organs shorter or longer, often very long, straight, divergent, or gently curved Faxonius. ee. The two parts of the male organs with rather short, sharply recurved tips, forming about a right angle with the basal part Bartonius. Paracambarus stands very isolated within the genus. We have regarded Procambartis as representing to a degree the old original stock of the genus. Paracambarus is more closely related to Procambarns than to any other subgenus, but there is no direct genetic connection imaginable. Although probably derived from common ancestors, each has apparently gone its own way of development, Paracambai'us being rather extreme and one-sided in certain characters. The only species, upon which this subgenus is founded, is new, and the description is as follows : CAMBARUS (PARACAMBARUS) PARADOXUS, new species. Diagnosis : Rostrum subovate, slightly concave above, mar- gins converging, without marginal spines, contracted into a short, triangular acumen ; carapace without lateral spines ; areola wide, slightly longer than half of the anterior section of the carapace ; first pereiopods with the chela subovate, swollen ; palm subcompressed, covered with strong, subsquamose tu- bercles, which form, near the inner margin, two to three irregu- lar, longitudinal rows ; fingers longer than the palm, with tu- bercles at the bases, and a longitudinal rib on the outer faces ; cutting edges with strong, irregular tubercles. Carpopodite granulated and tuberculated, spinose on inner and lower side. Only fourth pereiopods hooked in the male. First abdominal appendages of male with both parts in close apposition to the tips ; tips horny in the male of the first form, both with a slight outward and backward curve ; inner part on posterior side, a short distance from the tip, with a strong and long, spiniform process. Annulus ventralis, of the female forming an almost semicircular, transverse elevation, convex anteriorly, depressed 4 ORTMANN and concave posteriorly. Sternum between fifth pereiopods with a strong, triangular, anteriorly directed, spiniform process. Description of adult male of 'Jirsl form : Rostrum subovate, upper face slightly concave, margins elevated, converging, without marginal spines, contracted into a short, triangular acumen, which is shorter than the width of the rostrum at the base. Postorbital ridges subparallel, ante- riorly without spines. Carapace rather compressed, covered with punctations, which are rather large on gastrical region and base of rostrum ; sides of carapace finely granulated, granules more distinct on hepatical region. Suborbital angle blunt. Branchiostegal spine short, tuberculiform ; cervical groove slightly sinuate ; no lateral spines on the sides of the carapace ; areola wide, with four to five irregular rows of punctations, slightly longer than half of the anterior section of the carapace (including rostrum). Abdomen as wide as, and longer than, carapace ; basal seg- ment of telson with three or four spines on each side ; posterior segment semicircular. Eftistoma with anterior part broadly triangular, sharply pointed in the median line ; lateral margins concave anteriorly, convex posteriorly ; aniennal scale broad, greatest width ante- rior to the middle ; flagellum rather short, reaching to the second or third abdominal segment. First -pcreio-pods rather stout; hand elongated-ovate, slightly compressed ; surface with strong, subsquamiform tubercles, dif- fering in color from the surface of the hand, being, in alcoholic specimens, bluish black, while the rest of the hand is brownish yellow ; tubercles irregularly distributed, but with the tendency to form two or three rows near the inner margin, and slightly more crowded on the rounded outer margin of the hand ; on under surface of hand, the tubercles are more remote from each other, and not colored differently from the surface. Fingers distinctly longer than the palm, slightly gaping at the bases, each with a smooth longitudinal rib on outer and inner face, included by rows of punctations ; tubercles of palm extending upon bases of both fingers, and forming a short row upon prox- imal part of outer margin of movable finger ; cutting edges with MEXICAN, CENTRAL AMERICAN', AM) CUBAN CAMBARI 5 irregular, strong tubercles ; tips horny, and generally another horny tooth a short distance from tip on cutting edge of the im- movable finger. Carpopodite short, with a longitudinal sulcus above, granu- lated and tuberculated ; tubercles forming one or two spines on distal end of inner margin, and two other spines on lower sur- face, one on anterior margin, the other at the lower articulation with the hand. Meropodite granulated, but almost smooth on the larger portion of outer and inner face ; several strong tuber- cles at distal end of upper margin ; inner and outer lower margins each with a row of strong, spiniform tubercles, the outer row shorter. All the tubercles of the chelipeds appear squamiform on account of a fringe of short, stiff hairs at their anterior edges. Ischioftodite of fourth fierct'oflods with a strong hook ; this hook has a subcompressed, broad base, and is subcompressed, but narrower at the tip, and is slightly twisted. The ischiopo- dite of the third pereiopods is without hook, and there is only a slight, almost imperceptible elevation at its inferior margin. Fig. i. Cambarus paradoxus, sp. n. First pleopod (right side) of male (I). a, outer view; b, inner view. Enlarged about tour times. First pleopods (see Fig. i) reaching to the middle of the bases of the third pereiopods, stout, slightly curved backward ; inner and outer parts subequal, in close apposition to the tips. Both tips curved gently backward, and slightly outward, horny ; inner part, on posterior margin, at a short distance from the tip, with a strong, spiniform process, going off at an acute angle, and being longer than the two tips of this organ. Male of the second form : Tips of inner and outer parts of 6 ORTMANN sexual organs, as well as the spiniform process, not horny ; hook of fourth pereiopods smaller and weaker. Female: Similar to the male, but chelae not so strong. An- nulus ventralis transversely semicircular, anterior margin con- vex, elevated, with a curved longitudinal fissure ; posterior margin with a subtriangular depression. Sternum between the fifth pereiopods with a triangular, spiniform process, directed forward, which fits into the depression of the annulus. Aside from the peculiarities offered by the subgeneric charac- ters, this species is also remarkable for its chelae, which differ in a number of features from the types of chelae usually seen in the genus Cambarus. Measurements : The following are the dimensions of the three type-speci- mens : c? (I) : total length 48 mm.; carapace 23; anterior part 15, posterior part 8 ; abdomen 25 ; hand 17, palm 7, fingers 10 ; width of hand 7. — c? (II) : total length 48.5 mm.; carapace 23.5, anterior part 15.5, posterior part 8 ; abdomen 25 ; hand 16, palm 6.5, fingers 9.5 ; width of hand 6. — 9 : total length 48 mm. ; carapace 23, anterior part 15, posterior part 8 ; abdomen 25 ; hand 15, palm 6.5, fingers 8.5 ; width of hand 6. The largest cT (I) measures 51 mm., and the largest 9 54.5 mm. Locality : Sierra de Zacapoaxtla, State of Puebla, Mexico. — L. Diguet coll. 1904 (" ruisseaux torrentueux des montagnes, a le cafiada de Tetela de Ocampo"). (Mus. Paris, numerous specimens.) II. CAMBARUS (PROCAMBARUS) PILOSIMANUS, new species. Diagnosis : Rostrum subplane, with a marginal spine on each side ; carapace with two lateral spines on each side ; areola nar- row, as long as, or longer than, half of the anterior section of the carapace ; first pereiopods with the chela long, subcylindri- cal, slightly compressed, covered with tubercle-like granules ; fingers about as long as the palm, each with a smooth longi- tudinal ridge on the outer side, for the rest densely pilose on MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 7 outer and inner sides, the hairs extending upon the distal part of the palm. (In young individuals, the pilosity is less marked or even absent.) Carpopodite and meropodite granulated, and with a few granules developed into sharp spines on the inner and lower sides (indistinct in old individuals) ; third pereiopods hooked in the male ; first abdominal appendages of male with inner part pointed and straight, longer and much thinner than the broad and blunt outer part; shoulder of anterior margin only slightly developed ; inner face flattened and only slightly dilated. Annulus ventralis of the female conically elevated. Description of adult male of the first form : Rostrum subplane, margins elevated, gradually convergent, slightly convex, chiefly so anteriorly, with a distinct marginal spine on each side a short distance from the tip ; acumen trian- gular, rather short, shorter than width of rostrum at base ; mar- gins of acumen hairy ; postorbital ridges subparallel, ending in a spine anteriorly ; carapace compressed, thickly and finely punctate, and finely granulated on the sides ; suborbital angle blunt ; branchiostegal spine small ; cervical groove sinuate, two lateral spines on each side behind the cervical groove ; areola very narrow, but not obliterated, with one irregular row of punc- tations, longer than half of the anterior section of the carapace (including rostrum). Abdomen about as long and as wide as the carapace; basal segment of telson with two (rarely three) spines on each side ; posterior segment broadly rounded, short. Epistoma with anterior part triangular, obtuse ; antcnnal scale broad, broadest in the middle ; flagellum longer than the carapace, but shorter than the whole body. First pereiopods elongated, subcylindrical ; hand elongated, slightly compressed, with subparallel margins, widest at the base of the fingers ; surface thickly granulate, granules tuberculi- form, rounded, a-ery distinct, subequal ; fingers about as long as the palm, both on outer faces with a smooth longitudinal ridge ; for the rest, the fingers are thickly pilose on outer and inner side, the pilosity extending a short distance upon the palm on both faces ; carpopodite subcylindrical, with an indistinct, longitudinal sulcus on upper side ; granulated everywhere, gran- 8 ORTMANN ules largest on inner side ; a granule each at the distal end of inner margin, on the anterior margin of inner side, and at distal end of lower margin, more strongly developed and subspini- form ( often only indistinctly so ) ; meropodite granulated, gran- ules indistinct on outer and inner faces ; a subspiniform one near distal end of upper margin, and several subspiniform ones on lower side (often indistinct). Ischiopodite of third pair of pcreiopods with a strong hook. Fig. 2. Cambarus filosimanus, sp. n. First pleopod (right side) of male (I), a, outer view; l>, inner view. Enlarged about four times. First pleopods (see fig. 2) rather short, straight ; anterior margin with an indistinct, blunt shoulder near the tips ; outer and inner part in close apposition to their tips ; tip of outer part very blunt and rounded, slightly compressed in the antero- posterior direction ; tip of inner part straight, thin and pointed, distinctly longer than outer part ; at its base, on the anterior side, in front of the shoulder, there is a short, procurved, horny spine ; inner part flattened on inner face, slightly dilated, with hairs radiating from an indistinct oblique rib. Male of second form: The horny spine of the copulatory organs is replaced by a small, soft, blunt tubercle. Young males (of first or second form), less than 50 mm. total length, differ in the areola, which is about as long as the ante- rior section of the carapace ; chelipeds shorter and weaker, their granulations indistinct; they have short, scanty hairs, and the fingers are not pilose; carpopodite with well developed spines; meropodite also with sharp spines; one near distal end of upper margin, one at distal end of outer lower margin, and one or two at distal end of inner lower margin ; besides, MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 9 there are one to three more, forming an irregular row in the middle of the lower side. Female: Young females are like young males, older indi- viduals have the pilosity of the fingers well developed, but the chelipeds are less elongated than in old males, and consequently comparatively broader. The spines of meropodite and carpop- odite of the chelipeds also have the tendency to disappear in very old individuals. Annulus ventralis a blunt, low, sub- conical tubercle, with an S-shaped longitudinal fissure. Mcasurc?nents : The following are the measurements of the two type-speci- mens : cT (I): total length 72 mm. ; carapace 36, anterior sec- tion 23, posterior section 13 ; abdomen 36; length of hand 30, width of hand 8. 9 : total length 62 mm.; carapace 31, an- terior section 20, posterior section 11 ; abdomen 31 ; length of hand 19, width of hand 6. The largest females measure 68 mm. ; the largest male is the above type. Localities : T}rpes and Cotypes : Coche, pres de la riviere de Coban, Guatemala. — Exped. du Mexique. Bocourt (Mus. Paris, 10 cf(I), 3 c?(II), 9 9).1 Belize, British Honduras. — Exped. du Mexique (Mus. Paris, id1 (I)). Remarks: There is quite a difference in the features of old and young individuals. Generally, in specimens less than 45 mm. long, the pilosity of the fingers is not developed, and merop- odite and carpopodite of the chelipeds possess sharp spines. There is a £,45 mm. long, which shows traces of pilosity, while two males of the first form, of 49 and 50 mm. respectively, do not show it. The smallest male of the first form that has it, is 58 mm. long. Upward of this size all specimens have the fingers densely pilose. The spines of the chelipeds disappear entirely only in the oldest individuals; the smallest male (first 1 I have not been able to locate this place, nor a river " Coban " ; but Coban is the well-known capital of the province of Alta Vera Paz. The river at Coban is called Rio Cahabon. Coban, Alta Vera Paz, is the locality for a species of Cambarus mentioned by Huxley (1S7S). IO ORTMANN form), in which they have disappeared, is 58 mm. long, but in another, 62 mm. long, they are still recognizable. Three other males of the first form, 69, 71, 72 mm., have no spines. In the females, the spines generally persist up to a size of 60 and 62 mm., but they are missing in two females of 62 and 68 mm. length. Cambarns pilosimanus is closely allied to C. williamsoni Ort- mann ' from Los Amates, near Izabal, Guatemala. Indeed, it may be identical with it. The difference of the pilosity of the chelse in old individuals of C. pilosimanus is very marked how- ever, but we are to bear in mind that the largest individual of C. •williamsoni was rather small (51.5 mm.). Aside from the pilos- ity of the chelse, the only important difference noted is in the male copulatory organs, C. filosimanus having the shoulder less developed, and the tips of the inner and outer part more strongly contrasted. But this difference is not necessarily spe- cific, since for the rest the copulatory organs of both species are built according to the same plan. Other differences are only slight and apparently unimportant. In the young of C. pilosi- manus, where the pilosity of the chelse is not developed, the car- popodite and meropodite always possess a number of sharp spines, while in C. williamsoni only in the very young are traces of such spines visible on the meropodite. In specimens of about the same size, the granulations of the hand are more distinct in C. williamsoni, although in old individuals of C. filosimanus the granules are much stronger than in any speci- mens of C. williamsoni that are known. Further, the hand of C. pilosimanus is comparativel}' less slender, and is broader than in C. williamsoni. The close affinity, if not identity, of these two species is also borne out by the geographical distribution, but the two known localities of C. pilosimanus are farther north than that of C. williamsoni. It is quite possible that additional material will demonstrate their identity, but for the present I separate them, since there is no individual among the material from the prov- ince of Izabal that shows any trace of the pilosity of the chelse. 1 Ann. Carnegie Mus., Ill, 1905, 439. MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI II III. CAMBARUS (PROCAMBARUS) MEXICANUS Erich son. Literature : see Faxon, Mem. Mus. Harvard, 10, 1885, 50, and : Camb. mex. Ortmann, Zool. Jahrb. Syst., 6, 1891, 12; — Faxon, Proc. U. S. Nat. Mus., XX, 1898, 649 ; — Hay, Amer. Natural., XXXIII, 1899, 959 and 964. Camb. (Cambarus) mex. Ortmann, Proc. Amer. Philos. Soc, XLIV, 1905, 101. Camb. (Procambarus) mex. Ortmann, Ann. Carnegie Mus., Ill, 1905, 438. I have examined the male of the first form of this species pre- served in the Philadelphia Academy, from Mirador, Mexico (already mentioned by Faxon). The copulatory organ belongs to the type of the subgenus Procambarus and is allied to that of C. williamsoni and flilosimanus. It differs in the very strongly developed shoulder, and the position of the horny, procurved spine, which is almost terminal on the inner part. The tips of inner and outer part resemble those of C. williamsoni. An additional locality for this species is represented in the collections of the Philadelphia Academy : Texolo, State of Vera Cruz, Mexico. — S. N. Rhoads coll. 1899. — 3 c? (II), 2 9. (Texolo is near Xico, on the branch road from Jalapa, distant about 15 miles from Jalapa.) In the males of the second form of this set, the shoulder of the sexual organs is not quite so sharp, and the inner part is more pointed. IV. CAMBARUS (PROCAMBARUS) CUBENSIS Saussure. Literature: see Faxon, Mem. Mus. Harvard, X, 1885, 51, pi. 2, f. 1 ; pi. 8, f. 5, and : Camb. cub. Faxon, Proc. U. S. Nat. Mus. 1885, 358; Hay, Amer. Natural., XXXIII, 1899, 959-963. Camb. (Cambarus) cub. Ortmann, Proc. Amer. Philos. Soc, XLIV, 1905, 101. !2 ORTMANN Camb. (Procambarus) cub. Ortmann, Ann. Carnegie Mus., Ill, 1905,438. Among the material from the Paris Museum, sent to me by- Professor Bouvier, the following specimens were present : i. i d (II), 2 9. Cuba; Peters. 2. 4 d (II), i 9. Cuba; Peters. (Nos. i and 2 apparently from the Berlin Mus.) 3. 2 d (I), 2 d (II), 4 9. "Amerique"; Morelet. (All badly damaged, but copulatory organs well preserved.) 4. 1 d (I), type of Saussure's C1. consobrinus. (Dry specimen, mounted upon a piece of pith ; badly damaged, and copulatory organs not visible.) The following remarks are to be made : 1. C. consobrinus Saussure l is undoubtedly identical with C. cubensis. Although in the present type-specimen the male organs are not visible, it agrees with C. cubensis in all other respects. It has a very small lateral spine on the carapace. But such a spine is also present in two specimens (d and 9) in our first set, while the third (9) has only a trace of it. In the five specimens of the second set, which are all very young, two males (II) have a small granule in its place ; the others are apparently smooth. Of the eight specimens of the third set, one (a male of the first form) shows a small tubercle, and two females have none. The rest is too poorly preserved. 2. The male copulatory organs (Fig. 3, a-c) need some dis- cussion. The description given by v. Martens (Arch. f. Naturg., 38, 1872, p. 129) is quite correct, disregarding a lapsus calami or misprint, that renders a certain passage unintelligible. V. Martens says (translated) : They consist of two parts " an outer one, which ends in a blunt point, and has the anterior margin near this point considerably swollen ; and an inner one, which extends beyond the former posteriorly, and forms on the inner side a plane, ovate face, -which is adjacent to that of the ap- pendage of the anterior side (' zvelche sich an die des Anhanges der vorderen Seite anlegt '). At its end there are two lobes, one in close apposition to the end of the outer part, the second one shorter, projecting separately forward, and more rounded." 1 Rev. Mag. Zool. (2), 9, 1857, p. 101, and Mem. Soc. Geneve, 14, 1S5S, 457, pi. 3, f. 21. MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 13 The words emphasized by me cannot be understood as they stand. But if we conjecture that v. Martens wrote or intended to write, instead of zwrderen (anterior), anderen (other), every- thing is clear : he meant to say, that the inner plane face of the inner part is adjacent to the identical face of the appendage of the otJicr side. Thus the whole description is intelligible, and indeed, it is a correct characterization of the chief features of this organ. It is very interesting to note, that already v. Martens attributes to the inner part two lobes, and his second one is clearly the acces- sorv spine, which is not horny in the male of the second form ; v. Martens, consequently, describes this organ of the male of the second form. He has also correctly interpreted this organ. There is also in our specimens an outer part, which ends bluntly, and has the anterior margin slightly swollen just below the tip. The inner part is dilated and flattened on the inside, and forms, on the anterior margin, near the tip, a sharp shoulder. Its posterior margin extends considerably beyond the margin of the outer part, which is due to the extreme dilatation of the inner face. Its tip is pointed, and has, in the second form, a rounded, pro- jecting lobe anteriorly. In the male of the first form, the tip of the inner part is more slender and thin, almost setiform, but soft (not horny). The projecting lobe is replaced by a slightly procurved, horny spine, which is two-pointed, one point being blunt, the other acute and thin. Faxon's figures (1885, pi. 8, f. 5, 5', 5", 5"') are only partly correct. There is hardly any objection to Fig. 5"', which repre- sents the inner view of this organ of the left side of the male of the second form. It shows plainly the pointed tip of the inner part and the lobiform accessory process, as well as the thickened anterior margin of the tip of the outer part. Fig. 5" represents the same organ from the outside. The different parts are recog- nizable, but the outer part is not marked off at the tip, and the accessory lobe of the inner part is rendered incorrectly (as a recurved, blunt hook). Fig. 5' is intended to represent the inner view of this organ of the left side in the male of the first 14 ORTMANN form ; the inner part is drawn correctly, showing the setiform tip and the horny spine ; this spine, however, is drawn triangu- larly-single-pointed, while it is really slightly procurved and two-pointed. The outer part is represented in this drawing by a blunt, conical process, while actually it resembles the con- dition seen in the male of the second form, being concealed by the inner part with the exception of the swollen anterior margin, which projects slightly. Fig. 5 (outer view of same organ) is Fig. 3. Cambarus cubensis Sauss. a, First pleopod (left side) of male (II), outer view; b, the same, inner view; c, tip of same organ of male (I), inner view; d, annulus ventralis of female. All figures enlarged. quite unintelligible ; the tip of the outer part is not correctly represented, while the horny process is much too thin and is recurved, instead of procurved. That the differences between Faxon's figures and our speci- mens are due to incorrect rendering of the object by the draughts- man, is evident from the fact that it is impossible to reconcile the different views (inner and outer) of the same object. Correct figures of the organ in question are submitted here. Thus the copulatory organs of C. cubensis clearly belong to the type of the subgenus Procambarus ; the outer part has no terminal horny teeth, but is soft and blunt ; the inner part is flat- MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 15 tened and dilated on the inside, with a shoulder on the anterior margin near the tip ; the end of the inner part has a soft tip, and, in addition, in the male of the first form, a horny spine, which is replaced, in the second form, by a blunt tubercle. C. cubensis is closely allied to the species williamsoni, pi'lo- simanus, and mexicanus, but differs in the following characters : (1) The dilatation of the inner face of the male copulatory organ is much more pronounced ; the tip of the inner part is more pointed, almost setiform, in the male of the first form ; the horny spine is two-pointed. (2) The rostrum has marginal spines ; these are also present in C. williamsoni and filosi- manus, but are absent in C. mexicanus. (3) The carapace has a small lateral spine, which is sometimes absent; this spine is always missing in C. mexicanus, while the other two species have two distinct lateral spines on each side. 3. Faxon's description of the annulus ventralis of the female (1. c, p. 52) is correct: " composed of a large anterior bilobed tubercle, and a smaller posterior tubercle." I only wish to add that the small posterior tubercle possesses the S-shaped longi- tudinal fissure commonly seen in Cambarus, and it seems to me that only this tubercle ought to be regarded as the annulus. I was able to observe the shape of the annulus only in the largest female of the first set ; in all other females, which are small, it is very indistinct, a fact that has also been noticed by Faxon. For the rest, this species has been well described by Faxon, but in the figure of the anterior part of the animal [pi. 2, f /), the marginal spines of the rostrum have been omitted. These spines are small, but present in all specimens at hand. V. CAMBARUS (CAMBARUS) WIEGMANNI Erichson. Camb. wiegm. Faxon, Mem. Mus. Harvard, X, 1885, 38 (liter- ature). — Hay, Amer. Natural., XXXIII, 1899, 959 anc* 9^4- Camb. (Cambarus) wiegm. Ortmann, Proc. Amer. Philos. Soc, XLIV, 1905, 102. Hagen's female type specimen in the Philadelphia Academy agrees rather well with a male of the first form present in the same collection. This latter one is from the Cope collections and represents a new locality for the species : 1 6 ORTMANN Lake Xochimilco, south of City of Mexico (Federal District). — E. D. Cope coll., 1885. This male has enabled me to draw up the following descrip- tion : Rostrum broad, moderately long, plane above ; margins ele- vated, slightly convergent anteriorly, near the tip more strongly convergent, and forming a short, subtriangular acumen ; no marginal spines nor marginal angles at base of acumen, and the elevated margins continued to the tip, which is bluntly pointed ; postorbital ridges divergent posteriorly, without spines anteriorly ; carapace ovate, slightly compressed, punctate, slightly granulated on the sides ; suborbital angle blunt, branchi- ostegal spine distinct, but blunt (tuberculiform) ; cervical groove sinuate ; no lateral spine ; areola longer than half of the anterior section of carapace, rather narrow in the middle, with two to three irregular rows of punctations. Abdomen as wide as, and slightly longer than, the carapace ; anterior segment of telson with three spines on each side ; pos- terior segment semicircular. Ejyistoma with anterior part almost semicircular, a little an- gular on the sides, and bluntly pointed at the middle ; antennal scale broad, broadest anterior to the middle ; jlagellum shorter than carapace (but damaged at end). Chclipeds with hand rather wide, not much swollen, com- pressed, with subparallel margins ; surface squamoso-tubercu- late, tubercles on inner margin more crowded and stronger, forming an irregular row of serrations ; fingers strong, about as long as the palm, with longitudinal ribs and punctations on outer face, and with squamiform tubercles at the bases ; cutting edges tuberculated, tubercles irregular, a larger one near the base of each finger, and another large one near the distal end of immov- able finger ; carpopodite squamoso-tuberculate, inner side with several spiniform tubercles, upper surface with a slight longi- tudinal sulcus; meropodite smooth, with a few tubercles near distal end of upper margin, and two rows of tubercles on lower margins, the outer ones shorter. Ischiofodite of third and fourth pereiopods with hooks, those of the third pereiopod are very small, but distinct and tubercu- MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 1 7 liform. Those of the fourth pereiopod very strongly devel- oped, swollen and inflated, tapering to a blunt point; coxofio- ditc of third pereiopod with a semicircular, elevated, compressed tubercle, that of the fourth pereiopod with a strong, triangular spine, directed outward ; that of the fifth pereiopod with a small, spiniform tubercle below genital opening, directed downward. Fig. 4. Cambarus -tuiegmanni Erichson. First pleopod (right side) of male (I), a, outer view; b, inner view. Enlarged about three times. First -plcopods (Fig. 4) rather long and slender for the sub- genus Cambarus, reaching to the coxopodites of the second perei- opods, almost straight, very slightly curved ; truncated at the tip, with three horny teeth, of which the outer one is compressed and truncated, crescentic in shape ; the inner tooth is broadly triangular, and the anterior is short and spiniform,1 the inner part of this organ terminating in an almost straight spine, which is only slightly directed outward, and is slightly longer than the truncated outer part, and has a distinct horn)' tip. Measurements : Total length 60 mm. ; carapace 29, anterior part of carapace 18.5, posterior 10.5; width of areola 1.75; abdomen 31 ; length of hand 25.5, width of palm 9.5 (Erichson gives the following figures: total length 52 mm., length of hand 17 mm., width of hand 6.5 mm. Hagen gives 66 mm. as total length.) Comparing the present male with the description of the spe- 1 This latter one seems to belong to the inner part; but I suspect strongly that such is the case also in other species of the subgenus. The homologies of the sexual organs of Cambarus are altogether not well understood, and urgently need a more close study. Proc. Wash. Acad. Sci., May, 1906. ORTMANN cies given by Erichson, and the discription of the female given by Hagen, there is hardly any difference. Hagen describes and figures the epistoma as triangular and rather acute, which is not the case in our individual, and further, Hagen gives only two lateral spines for the anterior section of the telson. These differences are of no consequence, variations in these charac- ters being frequent in other species. I have compared the female in Philadelphia, which served as the base of Hagen's description, and which, since the Berlin types of Erichson have disappeared, must be regarded as the type of the species, and I find it to agree in all essential characters with our male, chiefly so in the shape of body and rostrum. Thus I think, the present male ought to be referred to this species. As is evident from the characters of the male of the first form described above, C. wiegmanni belongs to the subgenus Cam- barns, to the section of C. blandingi, and the group of C. allem',1 and it has been assigned its correct position already by Hagen and Faxon (allied to C. barbatus). The sexual organs are peculiar on account of the crescentic, compressed and trun- cated outer horny tooth, and do not closely agree with any of the known species of the subgenus ; but just this feature agrees with the rt//£«z-group in so far as this group is characterized by peculiar and aberrant conformations of the tips of the sex- ual organs.2 In shape of carapace, areola and rostrum, this species agrees closely with C. evermanni, barbatus and alleni> and the rostrum represents a rather advanced stage of develop- ment, being broadly lanceolate, without any traces of marginal spines or even marginal angles in their place. It resembles to a certain degree, the rostrum of C. clyfeatus Hay3 from Bay St. Louis, Hancock Co., Miss., but in the latter form the rostrum is still broader, and almost rounded off at the apex. I should 1 See Ortmann, Proc. Amer. Phil. Soc. 1905, 98 and 100; Ann. Car. Mus., I9°5. 437 and 438. 2 The sexual organs agree most nearly with those of C. hinei Ortm. from Lou- isiana, with the exception that in the latter species the crescentic and truncated tooth is absent, and that the distal part of the organ is distinctly curved backward. See Ortmann in The Ohio Naturalist, VI, 1905, p. 402, fig. 1. Also the rostrum of C. hinei is transitional toward C. wiegmanni. 3 Proc. U. S. Nat. Mus., XXII, 1S99, 122, fig. 2, no. 1. MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 1 9 not be surprised, if this latter species, of which the male is un- known, should finally prove to belong to this group, and not to the second group of Faxon (affinity of C. cubcnsis) as Hay is in- clined to believe. The hooks of the ischiopodites of the pereiopods are very pecu- liar, and unlike anything else that is known in the genus. And further, the development of the spines and processes of the cox- opodites of the three last pairs of pereiopods is very unique ; such processes are indeed found in other species in the shape of tubercles or ridges on the fourth or fifth pereiopods, but they never assume such proportions as in this species, and the out- wardly directed spine of the coxopodite of the fourth pereiopod in C. wiegmanni is without parallel. Thus it seems that C. wiegmanni is to be regarded as a very peculiar, and, in certain features, extremely developed form of the subgenus Cambarus, which belongs to a rather advanced and modern group of it (a l/cni- group, see 1. c, p. 105) which is characteristic for those parts of the coastal plain of the south- ern United States, that are most recent geologically. Its pres- ence in Mexico is rather interesting, and the specialized char- acter points to a recent immigration into these parts. But we are to bear in mind that the a/lcni-gvoup in general is compara- tively poorly known and needs further study. VI. Subgenus CAMBARELLUS. For the species of this subgenus I am only able to add a few new locality records : Cambarus (Cambarellus) montczumce Saussure (Faxon, 1885, 121 ; 1898, 660). Neighborhood of City of Mexico : Laguna de Santa Isabel. — G. Seurat coll., 1897 (Mus. Paris, 1 c? (I), 1 ?). Mexico. — Mus. Paris, numerous specimens, collected by various persons, but without more explicit localities. Lake Xochimilco, south of City of Mexico (Federal Dis- trict). E. D. Cope coll., 1885 (Philadelphia Academy, 1 ?). Most of the specimens seen by the writer belong to the form tridens v. Mart. With Faxon, I do not believe that this is worth a varietal name. According to my observations, young 20 ORTMANN examples generally are tridens, while the typical form is found only among old individuals, and is comparatively rare. Cambarus (Cambarellus) montezumce dugesi Faxon (1898, 660,//. 66,/. /). Guadalajara, State of Jalisco, Mexico. — Diguet coll. (Mus. Paris ; many specimens). Same locality. — Duges coll. (Mus. Paris, 4 c?). State of Guanajuato, Mexico. — Diguet coll. (Mus. Paris, 4^,4?)- The latter locality is the type-locality recorded by Faxon. The specimens from Guadalajara have been mentioned by Bouvier as C. montezumce iridens (Bull. Mus. Paris, 1897, 224), but they clearly belong to this variety. Cambarus (Cambarellus) montezumce occidentalis Faxon, (1898, 661, pi. 66,/. 3, 4). Hot Springs, Huingo, State of Michoacan, Mexico. — S. N. Rhoades coll., 1899 (Philadelphia Academy ; many specimens).1 VII. SYNOPSIS OF THE CRAWFISH-FAUNA OF MEXICO, CENTRAL AMERICA AND THE WEST INDIES. Our knowledge of the chorology of the genus Ca.abarus, south of the United States, is rather poor. Crawfish are now known from Mexico, Guatemala, British Honduras, and Cuba, but not only is the morphology of these forms not well under- stood, but also we have only a few and often doubtful or unre- liable locality-records. In order to call attention to this lack in our knowledge, I want to condense here the known facts, and point out the questionable records. Four subgenera are represented in this southern section of the range of the genus : Paracambarus, jProcambarus, Cam- barus, Cambarcllus. The first two are not found in the United States, while the other two are. Cambarus is largely distrib- uted in the United States, and has its main range there, only one species having invaded Mexico. Cambarcllus has its main abode in Mexico, and only one species is known from a single locality in Louisiana (New Orleans). 1 Huingo is near Lake Cuitzeo, and site of large salt works by evaporation from natural springs flowing into the lake. Crawfish were numerous in these springs and streams (communication from Mr. S. N. Rhoades to the writer). MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 21 The following is a list of the known species and their dis- tribution : i. Cambarus {Paracambar us) -paradoxus Ortmann. Tetela, Sierra de Zacapoaxtla, State of Puebla, Mexico. 2. Cambarus {Procambarus) digucti Bouvier. Tributaries of Rio Santiago, State of Jalisco, Mexico (Bouvier). Guadalajara, State of Jalisco (Faxon). Ameca, State of Jalisco (Faxon). Hacienda de Villachuato, State of Michoacan (Faxon). The location of this hacienda is unknown. This species consequently belongs to the Pacific drainage in western Mexico. 3. Cambarus {Pro cambarus) williamsoni Ortmann. Los Amates, Province of Izabal, Guatemala (Atlantic drain- age). 4. Cambarus {Procambarus) pilosimanus Ortmann. Coche, on river Coban, Guatemala (probably Coban, Prov- ince of Alta Vera Paz, see above p. 9, footnote). Belize, British Honduras. (Both localities in Atlantic drain- age.) 5. Cambarus {Procambarus) mexicanus Erichson. Mexico (Erichson, Ortmann). Probably the City of Mexico is meant, since the presence of this species in its neighborhood is confirmed by other records from the Federal District. Santa Maria, Mexico (Faxon). There are half a dozen places of this name in various parts of Mexico. One is close to the City of Mexico, and thus we may assume that this is intended. Tomatlan, Mexico, " terres chaudes " (Saussure). Again there are several places of this name in Mexico : one is south of the City of Mexico, in the Federal District, another in the State of Jalisco, not far from the Pacific Ocean ; a third one about 10 miles south of Huatusco, in the State of Vera Cruz. Saussure's specification: "terres chaudes" renders it safe to assume that this latter locality in the State of Vera Cruz was intended. Puebla, State of Puebla (v. Martens). Mirador, Mexico (Faxon). This is an observation station in the State of Vera Cruz, 190 15' N., 960 40' W., alt. 3,600 feet. I was not able to find it on any of the maps at my disposal. 22 ORTMANN Texolo, State of Vera Cruz (see above p. u). Thus this species is known from the states of Mexico (Federal District), Puebla, and Vera Cruz, that is to say, from the central plateau and from the Atlantic slope. 6. Cambarns {Procambarus) cubensis Erichson. Cuba. Saussure gives the interior of this island, and Faxon creeks in a little town opposite Havana. 7. Cambarus {Cambarus) wiegmanni Erichson. Mexico (Erichson, Hagen), probably the City of Mexico. Lake Xochimilco, Federal District (see above, p. 16). Jalapa, Mexico (Faxon). This is very likely Jalapa in the State of Vera Cruz, although there are other places of this name in Mexico. These localities are on the central plateau and the Atlantic slope. This species has been recorded with some doubt from the Isthmus of Tehuantepec (Faxon), but we would better drop this for the present. 8. Cambarus (Cambarellus) chapalanus Fax. Lake Chapala, State of Jalisco, Mexico (Pacific drainage). 9. Cambarus {Cambarellus} montezumce Sauss. a. Typical form (including var. tridens v Mart.). Chapultepec, Federal District, Mexico (Saussure). West of City of Mexico. Lake Texcoco, Federal District (Faxon). East of City of Mexico. Lake Xochimilco, Federal District (see above, p. 19). South of City of Mexico. Laguna de Santa Isabel, near City of Mexico (see above, p. 19). I have not been able to locate this, but the statement that it is near the City of Mexico associates this with the first three records given. Puebla, State of Puebla, Mexico (v. Martens). Lake San Roque, Trapuato, Mexico (Faxon). I have not been able to find this locality designated on any of the maps, or in any gazetteer consulted by me. Vera Cruz, Mexico (Ortmann) (Zool. Jahrb. Syst., 6, 1891, p. 12). This locality should be considered as doubtful till con- firmed. The specimens upon which this record was founded, MEXICAN, CENTRAL AMERICAN, AND CUBAN CAMBARI 23 were secured from a dealer, and it was not stated whether the city or the state of Vera Cruz was meant. Moreover, it is well known how utterly untrustworthy dealers' localities are. The presence of this species in its typical form is thus posi- tively known only on the central plateau, near the cities of Mexico and Puebla. b. Cambarus (Cambarellus) monteztnnce dugcsi Faxon. State Guanajuato, Mexico (Faxon, Mus. Paris). Guadalajara, State of Jalisco (Bouvier, Mus. Paris, see above, p. 20). Pacific drainage. c. Cambarus (Camba reikis) montczumce areolalus Faxon. Parras, State of Coahuila, Mexico (Faxon). Northern part of central plateau. d. Cambarus (Cambarellus) montezumai occidcntalis Faxon. Mazatlan, State of Sinaloa, Mexico (Faxon). Huingo, State of Michoacan, Mexico (see above, p. 20). Pacific drainage. It is hard at present to draw any conclusions from these meagre records. Only a few remarks may be made, but it is very likely that they will be subject to revision when more in- formation comes to hand. The subgenus Procambarus possesses its most primitive form (C. digueti) in the western extremity of its range (mountainous region toward the Pacific slope). The most extreme species (C. cubensis) is found at the eastern extremity of the range, in Cuba. Intermediate forms are found on the central plateau and the eastern hot country of Mexico (C. mexicanus), in Guate- mala, and British Honduras (C williamsoni and fi/'los/mattus), thus indicating the direction of the dispersal (see Ortmann, Ann. Cam. Mus., 3, 1905, p. 441). Thus Procambarus not only points out the original home of the genus in a general way (Mexico), but indicates especially the western portions of this country. However, further research is very desirable. Cambarus wiegmanni is the only representative of the sub- genus Cambarus in Mexico ; the bulk of this subgenus being found in the United States, chiefly in the southern parts (see 24 ORTMAXX Ortmann, P. Amer. Philos. Soc, 44, 1905, p. 103 f.). Moreover, it belongs to a rather advanced and modern group of this sub- genus (alleni-gvoup), which is characteristic for the late Terti- ary and Post-tertiary plains of the South Atlantic and Gulf bor- der in the United States. Thus it is very probable, that this species immigrated into Mexico from the United States, repre- senting a direction of dispersal opposite to that generally ob- served in the genus, for which, however, at least one other in- stance is known (C clarki, 1. c, p. 126). The known habitat of C. wicgmanni appears rather isolated, and it is much to be de- sired that northern Mexico and southern Texas should be in- vestigated with a view to settle this question. The most primitive species of the subgenus Cambarellus (C shufeldti) is found in Louisiana. C. chapalanus appears slightly more primitive compared with C. montezumce and its varieties, and is found in western Mexico. Of the montezumce forms, areolatus is the most primitive and the most northern, nearest to the United States, while occidenlalis is the most advanced (shape of rostrum), and is western in Mexico. Thus the evidence is partly contradictory. Leaving out chapalanus, the general trend of the evidence is to show that the subgenus originated in the southern United States and immigrated into Mexico, first into the central plateau, then into the Pacific slope. This would, consequently, offer a third case of reversed migration in this region, and my map (1905, pi. 3) should be changed accordingly (the brown color). This would also not conflict with the morphological characters of Cambarellus, the shape of the sexual organs inclining more toward the subgenus Faxonius of the United States, than toward the Mexican sub- genera. But I must confess, that the evidence for this assump- tion appears at present too scanty, so that we can hardly call it more than a mere theory. It is chiefly with a view to instigate further research on these questions that I have ventured to ex- press at all an opinion on this topic. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 25-40 May iS, 1906 THE GEODETIC EVIDENCE OF ISOSTASY, WITH A CONSIDERATION OF THE DEPTH AND COM- PLETENESS OF THE ISOSTATIC COMPEN- SATION AND OF THE BEARING OF THE EVIDENCE UPON SOME OF THE GREATER PROBLEMS OF GEOLOGY.1 Introduction. By O. H. Tittmann.2 It is my pleasant duty to introduce to you the speaker of the evening, but I shall ask your indulgence for a few moments while I explain to you the reasons which lead up to the investigation of which he will give you an account. You are aware that the governments of the world maintain an international Geodetic Association under the terms of a formal convention for the purpose of furthering the admeasurement of the earth. The countries which are parties to this convention are Great Britain, whose monumental work in India is of the greatest importance and which is also conducting geodetic operations in South Africa ; Germany, the originator of the Association ; France, the mother of geodesy; Russia, Austria-Hungary, Italy, Spain, The Netherlands, Norway, Sweden and Denmark. The Orient is repre- 1 Published with the permission of the Superintendent of the Coast and Geodetic Survey. 2 At a meeting of the Washington Academy of Sciences on the evening of April 14, 1906, this paper was read by Mr. Ilavford. It has been thought desir- able to publish in this connection the introductory remarks made by Mr. O. H. Tittmann, Superintendent of the Coast and Geodetic Survey, and the discussion by Major Clarence E. Dutton. Proc. Wash. Acad. Sci., May, 1906. 25 26 HAYFORD sented by Japan, and this continent by the United States and Mexico. In South America, Brazil, the Argentine Confederation, Chili and Peru, are organizing geodetic surveys and will doubtless become parties to the convention which recognizes the determination of the earth's figure and size as an international function. As the arc of Peru, which was recently remeasured by the French, was measured by a European nation, the United States is the only country among all the American nations, which has contributed to our knowledge of the earth's figure. Leaving out of consideration for the present several minor arcs along the Atlantic seaboard the Coast and Geodetic Survey published in the year 1900 the results of the measurement of the trans- continental arc along the 39th parallel. This was followed in the year 1901 by an account of the oblique arc extending from Eastport, Maine, to New Orleans, La. Since then it has published the results of its trigonometric survey extending from the southern boundary of California to Monterey Bay, California. These great triangula- tions were begun in many separate localities and when they were connected it became necessary to adopt a uniform system of coordi- nates for the whole country. The advantage of doing this was recog- nized by the engineers of the Army, under whom an extended trigono- metric survey covering the region of the Great Lakes had been completed, and their triangulation, 1 aving been connected with that of the Coast and Geodetic Survey, was, by cooperation between the Departments having charge of these organizations, referred to the same datum adopted by the Coast and Geodetic Survey. The earlier coastwise triangulations of the Coast and Geodetic Survey were pro- jected upon the Bessel spheroid. As the work progressed it became evident that the Clark spheroid of 1S66 was in the region of the United States better adapted for the purpose of a reference spheroid than the former, and it was substituted for the Bessel spheroid. It also became clear that for purely geographic purposes the Clark spheroid would suffice, or at any rate that an attempt to substitute, if it were possible, a closer osculating spheroid would involve enormous labor without compensating advantages. This point of view established the policy of referring all the trigonometric work on the United States to a com- mon origin of coordinates on the Clark spheroid of 1S66 on which much of it had already been developed. Side by side with the computations necessary in this great under- taking the investigation of the form of the geoid involving the anom- alies which were developed by the trigonometric and astronomical operations was carried on, for the adoption of a reference spheroid THE GEODETIC EVIDENCE OF ISOSTASV 27 for geographical purposes did not relieve us of the duty of trying to explain the discrepancies between it and the existing geoid. The discussion of the arcs hitherto published proceeded along the conventional lines of treating these anomalies, that is, the deflection of the vertical as though they were accidental errors of observation, though it was well understood that such is not the case. When, however, the arcs were all connected it became possible to treat the triangulations in a much more general way and to have regard to the surface within the area covered by them, which would most nearly represent the geoid. To this very difficult task Mr. Hayford addressed himself. He first devised methods of computation which brought the investigation within reach of the limited force of computers at his disposal. What he will tell you to-night in brief, will be submitted in more detail to the International Geodetic Association as a contribu- tion from this country to a problem which all are trying to solve. The results will, I believe, make evident to you the great power of geometry, using the word in its etymological sense, to disclose facts which are of the greatest importance to geology and geophysics. The Paper. By John F. Hayford, C.E.1 My intention is to present to you a general view of an investi- gation which is still in progress, to state some of the principal conclusions reached, and to indicate very briefly some of the relations of these conclusions to conclusions reached by others along very different lines of investigation. At the outset it is necessary to have a clear conception of the condition called isostasy. If the earth were composed of homogeneous material, its figure of equilibrium, under the influence of gravity, and of its own rotation, would be an ellipsoid of revolution. The earth is composed of heterogeneous material which varies considerably in density. If this heterogeneous material were so arranged that its density at any point depended simply upon the depth of that point below the surface, that is, if all the material in each horizontal stratum were of one density, the figure of equilibrium would still be an ellipsoid of revolution. 1 Chief of Computing Division and Inspector of Geodetic Work, Coast and Geodetic Survey. 28 HAYFORD If the heterogeneous material composing the earth were not arranged in this manner at the outset the stresses produced by gravity would tend to bring about such an arrangement. But as the material is not a perfect fluid, as it possesses considerable viscosity, at least near the surface, the rearrangement will be imperfect. In the partial rearrangement some stresses will still remain, different portions of the same horizontal stratum may have somewhat different densities, and the actual surface of the earth will be a slight departure from the ellipsoid of revolution in the sense that above each region of deficient density there will be a bulge or bump on the ellipsoid, and above each region of excessive density there will be a hollow, relatively speaking. The bumps on this supposed earth will be the mountains, the plateaus, the continents — and the hollows will be the oceans. The excess of material represented by that portion of the continent which is above sea level will be com- pensated for by a defect of density in the underlying material. The continents will be floated, so to speak, upon the relatively light material below them and, similarly, the floor of the ocean will, on this supposed earth, be depressed because it is com- posed of unusually dense material. This particular condition of approximate equilibrium has been given the name, isostasy. Is the earth to-day in this condition? In connection with a study of this question it is convenient to define two or three phrases which will be found useful and in defining them to add precision to our conception of isostasy. The adjustment of the material toward this condition, which is produced in nature by the stresses due to gravity, may be called the isostatic adjustment. The compensation of#the excess of matter at the surface (con- tinents) by defect of density below, and of surface defect of matter (oceans) by excess of density below may be called the isostatic compensation. Let the depth within which the isostatic compensation is com- plete be called the depth of compensation. At and below this depth the condition as to stress of any element of mass is iso- static, that is, any element of mass is subject to equal pressures from all directions as if it were a portion of a perfect fluid. THE GEODETIC EVIDENCE OF ISOSTASY 29 Above this depth, on the other hand, each element of mass is subject in general to different pressures in different directions, to stresses which tend to distort it and to move it. The idea implied in this definition of the phrase "depth of compensation," that the isostatic compensation is complete within some depth much less than the radius of the earth, is not ordinarily expressed in the literature of the subject, but it is an idea which it is difficult to dodge if the subject is studied care- fully from any point of view. The data to be discussed to-night indicate that all the isostatic compensation occurs within a thin surface layer of the earth, extending down J^ or possibly ^V of the depth from the surface to the center. The geodetic evidence which may be used to test whether or not the condition called isostasy exists, consists of determinations of gravity and of determinations of deflections of the vertical. It is to the evidence furnished by the latter that I wish to call your attention to-night. Within the limits of the United States and connected by continuous triangulation, which has all been reduced to one datum, 507 astronomic determinations have been made; 265 of latitude, 79 of longitude, and 163 of azimuth. These furnish that component of the deflection of the vertical which lies in the meridian at 265 stations, and the prime vertical component at 232 stations. These astronomic stations are scat- tered from Maine to southern California, in portions of 33 states. This triangulation and the astronomic determinations connected with it are furnished to the world by the Coast and Geodetic Survey and the Lake Survey and constitute a magnificient contribution by the United States toward the determination of the figure and size of the earth. In deriving the figure and size of the earth from observed deflections of the vertical the usual practice has been to ignore the topography around each station, except that occasionally observed deflections have been rejected because they were in or near a mountainous region. The effect of a possible systematic distribution of density in each horizontal stratum of the earth has also been ignored. The topographic irregularities are visible and known. The systematic distribution of density below the surface is invisible 30 HAYFORD and unknown. The topographic irregularities and the distri- bution of density each affect the deflections of the vertical. Therefore, each should be taken into account as far as possible in any attempt to derive the figure and size of the earth from geodetic measurements. They are so taken into account in the investigation now in progress in the Coast and Geodetic Survey. This investigation seeks to determine not only the figure and size of the earth but also to determine whether the condition called isostasy exists with its peculiar distribution of sub-surface densities, and if so the depth within which the isostatic compen- sation is complete. Several complete and independent solutions by least squares of the problem of determining the figure and size of the earth have been made in this investigation upon different assumptions as to isostasy and depth of compensation. The residuals of these different solutions, expressing the degree of harmony brought about by the different assumptions, furnish the evidence as to which of the assumptions is nearest the truth. One solution was made on the assumption that the condition called isostasy does not exist, that no isostatic adjustment occurs when vast masses are eroded from high parts of the earth's surface, and are transported and deposited on the low parts — that the earth is so rigid as to support the continents as local excesses of mass. It is equivalent to the assumption that the depth of isostatic compensation is infinite. To make this solution it was necessary to compute the effect of all the topography for a considerable distance from each station. The computation was made to cover all topography within 2,564 miles of each of the 304 stations. The usual solution was also made. This solution is based upon the tacit assumption that no relation exists between deflec- tions of the vertical and the topography. It is equivalent to the assumption that isostatic compensation exists and is complete at depth zero — that there exists immediately below every elevation (either mountain or continent) the full compensating defect of density, and that at the very surface of the ocean floor there lies material of the excessive density necessary to compensate for the depression of that floor. Under no other condition can THE GEODETIC EVIDENCE OF ISOSTASY 3 1 it be true that the observed deflections of the vertical are inde- pendent of the known topography. This assumption, tacitly made in the usual determinations of the figure of the earth, such for example, as the Clark and Bessel determinations, represents an impossible condition. It is a limiting case. If the depth of compensation is finite, the deflections of the vertical due to topography will be partly counterbalanced by the contrary deflections due to defects and excesses of density below the surface. The counterbalancing will be more com- plete the greater the distance from the station to the partic- ular topographical features under consideration. Given an as- sumed depth within which the compensation is complete, and assuming that the compensation is uniformly distributed through that depth, it is a simple matter to compute the corresponding deflections. The computation takes account fully of the amount by which the plumb line is drawn toward a given mountain range by the direct attraction of the mass of the range, and also of the smaller effect of the contrary sign produced upon the plumb line by the relative defect of density below the range. Three complete solutions were made in turn upon the assump- tions that the depth of compensation is 101, 75, and 71 miles. These particular assumed depths were based upon preliminary examinations. A comparison of the five solutions corresponding to assumed depths of compensation, infinity, 101 miles, 75 miles, 71 miles, and zero, showed that the sum of the squares of residuals was least for the 71-mile solution. Therefore, 71 miles is the most probable of these five assumed values for the depth of compensation. How strong and clear is the evidence that the actual condi- tion of the earth is that called isostasy, with the isostatic com- pensation uniformly distributed within the depth of 71 miles, rather than that it is an earth in which there is no isostatic compensation, on which the continents and oceans are main- tained by rigidity? Compare the 71-mile solution with that for assumed depth infinity, the last named being the solution cor- responding to extreme rigidity. The sum of the squares of the residuals in the former solu- tion is 8,000 and in the latter is 65,000, more than 8 times as 32 HAYFORD large. In the former solution there are but 19 per cent, of the residuals greater than 5" and the maximum residual is 16", whereas in the latter 66 per cent, of the residuals are greater than 5" and the maximum residual is 44". In the former solu- tion the average residual is 3".i and the latter 8". 8. The evidence shows clearly and decisively that the assump- tion of complete isostatic compensation within the depth of 71 miles is a comparatively close approximation to the truth, that the assumption of extreme rigidity is far from the truth — that the United States is not maintained in its position above sea level by the rigidity of the earth, but is, in the main, bouyed up, floated, upon underlying material of deficient density. The conclusions just stated were based upon the 507 residuals considered as one group. The residuals have been examined in separate groups of 25, each group covering a small region. Not a single group of 25 contradicts the conclusion just stated. It is certain that for the United States and adjacent regions, including oceans, the isostatic compensation is more than two- thirds complete — perhaps much more. The departure from perfect compensation may be, in some regions, in the direction of over-compensation rather than under-compensation but in either case the departure from perfect compensation is less than one-third. In terms of stresses, it is safe to say that these geodetic ob- servations prove that the actual stresses in and about the United States have been so reduced by isostatic adjustment that they are less than one-tenth as great as they would be if the con- tinent were maintained in its elevated position, and the ocean floor maintained in its depressed position, by the rigidity of the earth. In order to secure the greatest possible accuracy in deriving the figure of the earth it is necessary to determine as accurately as possible the depth at which the isostatic compensation occurs. This is also of great importance on account of its bearing on the greater problems of geology. With what degree of accuracy does this geodetic investigation fix the depth of compensation? When all the evidence from the solutions for depths infinity, 101 miles, 75 miles, 71 miles, and zero, is also taken into ac- THE GEODETIC EVIDENCE OF ISOSTASY 33 count, it appears that, if the compensation is uniformly distrib- uted with respect to depth, the most probable value of the limit- ing depth is 71 miles and that it is practically certain that the limiting depth is not less than 50 miles nor more than 100 miles. No conclusive evidence has yet developed in the investigation that the depth of compensation is different for different parts of the United States. In all that has been said thus far, and in the corresponding parts of the investigation, it has been assumed that the compen- sation is uniformly distributed with respect to the depth. This assumption is not necessarily true and it must, therefore, be examined. It was adopted as a working hypothesis because it happened to be the one reasonable assumption which lends itself most readily to computation, and because it also seemed to the speaker to be the most probable simple assumption. It is probably impossible to determine the distribution of the compensation with respect to depth from investigations based simply upon deflections of the vertical. Possibly pendulum observations combined with deflection observations may detect the manner of distribution. All that can be done with deflections of the vertical is to determine the depth of compensation on various assumptions in regard to distribution with respect to depth. Just as the limiting depth of the compensation, if it is uni- formly distributed with respect to depth, has been determined by this investigation to be about 71 miles, so it has also been determined by a later portion of the investigation that if the compensation is greatest at the surface and diminishes uniformly with respect to depth until it fades out to zero, the limiting depth is about 109 miles. Again, it has been determined by the investigation that if the compensation all occurs within a stratum ten miles thick the bottom of the stratum is at a depth of about 37 miles. My belief is that the depth 71 miles and the corresponding assumed manner of distribution are nearer the truth than either the depth 37 or 109 miles with its corresponding assumption. This belief rests on insecure foundation. If anyone will tell me the manner of distribution of the compensation with respect to 34 HAYFORD depth I believe that from the observed deflections of the vertical now available the limiting depth of compensation can be derived with reasonable certainty, with an error of less than 25 per cent. Thus far this talk has been confined to the direct deductions from the geodetic observations. In this field the speaker en- joys a peculiar advantage in being in unusually close touch with the subject. He has no such advantage with respect to the suggestions which are about to be made on the bearing of these deductions upon some of the greater problems of geology. Nevertheless, the suggestions seem to be desirable in order to indicate some of the important relations of the geodetic investi- gation to other investigations. The direct deductions from the geodetic observations, which have been stated, are a safe and strong foundation which can- not be shaken. The superstructure of suggestions which I am about to build upon it is relatively weak and unsafe. Please remember if you do succeed in knocking down the superstruc- ture, that the foundation is still in place and awaiting an abler architect than I am to put a good superstructure upon it. The fact is established by this geodetic investigation that the isostatic adjustment brought about by gravity has reduced the stresses to less than one-tenth of those which would exist if the continents and oceans were maintained by rigidity. This gives new and very strong emphasis to the idea that the earth is a failing structure, not a competent structure. The mechanics of the two kinds of structures are very different. Geologists, and others who deal with the mechanics of the earth, seem to realize only a part of the time that the earth is a fail- ing structure. Even during the periods of realization it is seldom that one acts upon the supposition that the earth is so utterly in- competent to bear the stresses brought upon it as this geodetic investigation indicates. Let me cite two examples taken from speakers before this Academy and in this room within a year. One speaker, in stating the various methods of estimating the age of the earth, referred to the fact that there is no great excess of land surface about the equator as compared with the remainder of the earth. It has been urged that this indicates THE GEODETIC EVIDENCE OF ISOSTASY 35 that the earth solidified in comparatively recent time. For other- wise, under the influence of a decreasing rate of rotation, the water would draw away from the equator and leave it high and dry. Now if the earth is so weak that it can stand but a small fraction of the weight of a continent before isostatic readjust- ment begins to take place, of course the equatorial protuberance due to decreasing rotation will be leveled down by failure and isostatic readjustment practically as fast as it develops, even if no other actions tend to level it down. Hence the study of the distribution of land with respect to latitude furnishes a measure of the earth's weakness, not of its age. Another speaker quoted an article by Mr. G.Johnstone Stoney in which it is suggested that the permanence of the continents is due to elastic expansion of all the underlying material when load is removed by erosion. This idea, viewed in the light of geodetic evidence, seems to be extremely absurd, for it assumes the earth to be perfectly elastic — a competent structure — to great depths, whereas the earth is apparently inelastic to a high degree even near the surface and is apparently failing continuously under the stresses brought to bear upon it. The expression "failing continuously" has been used pur- posely. It is possible that the continents and oceans are in then- present positions because light material accumulated at the out- set in the places now occupied by the continents, and heavier material accumulated where the deep oceans now lie. This would constitute an initial isostatic adjustment. But the geologic evidence is overwhelming that within the interval covered by the geologic record many thousands of feet of thickness have been eroded from some parts of the earth and have been trans- ported to and deposited upon other parts. If isostatic readjust- ment had not also been in progress during this interval, it would be impossible for the isostatic compensation to be so nearly complete as it is at present. For example, it is estimated by competent authority that a series of strata from 8 to 10 miles thick have been eroded and carried away from certain areas in the western part of the United States, which are now broad and lofty platforms carry- ing mountain ridges. The present elevation of these areas is 36 HAYFORD less than three miles — the average elevation, not the elevation of the summits. Yet the present isostatic compensation, as already stated, departs not more than one-third from present perfection. The only reasonable explanation is that the iso- static readjustment keeps pace approximately with erosion and deposition. Upon the basis that the isostatic compensation is complete and uniformly distributed throughout the first 71 miles of depth, will the computed variations of density be so great as to raise a doubt of the validity of the conclusions which have been drawn? The highest large area within the region covered by this in- vestigation is the region southwest of Denver, Colorado, with an elevation of about 11,000 feet or 2.1 miles. This is 3 per cent, of 71 miles. Hence, on the basis stated, the average density of the material beneath this region is 3 per cent, less than that beneath the areas along the coast which lie practically at sea level. The deepest ocean area of considerable size within the region of the investigation is in the Atlantic, north- east of the Caribbean Islands, with a depth of 3,000 fathoms or 3.4 miles. On the basis stated the average density of the material underlying this deep spot is only 3 per cent, greater than that of the material under areas which lie at sea level. This computed variation in density is small, much smaller than the variations in density between different rock samples from different regions. Hence it presents no contradiction to the supposition that the location of continents and oceans may be due to initial differences of density in the materials. But if there is a continuous isostatic readjustment in progress it is apparently necessary to believe that a given material may change in density as much as 3 per cent., under the varying conditions as to pressure (and possibly temperature) to which it is subjected within the first 71 miles of depth in the earth. Both laboratory obvervations and geologic observations indi- cate that this is not only possible but probable. The elastic effects probably cooperate in producing such changes of density, but probably play a minor part only. Laboratory experiments have established as a general law of chemistry that increase of pressure favors such chemical THE GEODETIC EVIDENCE OF ISOSTASY 37 changes as are accompanied by decrease of volume, that is, in- crease of density. So, too, it is a law well established by laboratory investiga- tions that the mass of a given gas that will remain in solution in a given liquid is proportional to the pressure. According to this law, known as Henry's Law, wherever beneath the surface of the earth gases and liquids are in contact an increase of pres- sure will drive more gas into solution and so increase the den- sity of the mixture. A decrease of pressure will cause apart of the gas to come out of solution and decrease the density of the mixture. Considering solution as a chemical process this law is but a specific example of the general law stated a moment ago. Many other specific examples might be given of changes in pressure producing changes in chemical state and thereby changes in density. Very important among these, because it is a process appar- ently in progress very extensively, is the solution of rock con- stituents in water and redeposition with a net increase of density of the rock so modified. A quantitative study shows that changes of these kinds in a small part only of the materials in the heterogeneous mixture which makes up each cubic mile are sufficient to account for a change of 3 per cent, in the average density, and that isostatic readjustment brought about in part in this manner is not at all improbable. The consensus of geologic evidence also indicates the exist- ence of this relation of pressure, chemical state and density. For example, rocks which have been under great pressure be- cause they have been deep within the crust are, in general, more dense than those composed of the same proportions of the elements but which have not been subjected to great pressure. So, too, it is a general law of metamorphism that changes going on in rocks which are now near the surface but which formerly were deep-seated are changes which are accompanied by de- crease in density. The indications are, therefore, that when an elevated area under which there is complete isostatic compensation is un- 38 HAYFORD loaded by erosion the underlying material to a depth of 71 miles increases in volume mainly because of chemical changes induced by the decrease in pressure, and partly also because of changes in the gases from solution to the free state. This in- crease in volume raises the surface. It also increases the pres- sure at each level above the 71-mile depth, and tends to bring it back toward the value which it had at that level before the unloading. This expansion process alone is not sufficient, however, to maintain an isostatic adjustment indefinitely. As the process progresses — a continuous expansion in the underlying material keeping pace approximately with continu- ous unloading by erosion at the surface — the pressure near the bottom of the expanding column will become considerably less than it is at the same level in other areas at which no unloading by erosion is taking place. So, too, near the top of the expand- ing column the pressures will tend to be somewhat greater than at the same level in other areas. The result of these differences in pressure at any given horizontal surfaces will be to set up, sooner or later, a great slow undertow from the ocean areas toward the continents, and a tendency to outward creeping at the surface from the continents toward the oceans. Let me now emphasize the idea that the theory briefly sketched in the last few minutes is one which correlates many groups of observed facts. It obviously accounts for the marked general tendency for areas unloading by erosion to rise and those loading by deposi- tion to subside. The theory indicates how the changes in density which ac- company matamorphism are a part of the process of continent building. The theory also accounts for the tangential stresses along the earth's surface of which the crumpled strata, especially of mountainous areas, are the evidence. For the great undertow toward the continents is attached to the surface strata by con- tinuous material and tends to carry them inward. A great con- test is waged between the shearing stresses developed between the undertow and the surface strata on the one side, and the THE GEODETIC EVIDENCE OF ISOSTASY 39 compressive stresses exerted in a horizantal direction in surface strata, on the other side. The shortening of the surface strata by bending is a record of the extent to which the surface strata have suffered in the contest. According to this theory the undertow should be most power- ful a short distance inside the continental borders and hence the mountain building should be most active there. Many geolo- gists have stated this to be the fact. Again, according to this theory, such mountain ranges should be unsymmetrical, thereby indicating that the pressure came from the ocean side. Again, according to the geologists, many mountain systems show this effect as, for example, the Alle- ghenies. Many other points might be brought out. But the time is too short. So, too, the time has been too short to credit ideas to their originators, some of whom are present here to-night. I have tried simply to marshall the ideas and facts in such a way that their relations would become evident. Discussion. By Major Clarence E. Dutton. I have only words of praise for the paper of Mr. Hayford. He seems to have expressed very accurately the conception of isostasy. His definitions of isostatic adjustment and isostatic compensation are very good. The chief point in his paper which makes it a valuable contribution to science is his determination of the depth at which the compensation occurs and is probably limited. That determination proves to be of a greater depth than f had anticipated, but it is none the less satisfactory on that account. Indeed I think it is more satis- factory than I had anticipated. It gives a greater concentration to the isostatic effort and permits us to infer a larger amount of horizontal displacement in the underlying masses than if it were much deeper. Also his determination of the amount of strain to which the rocks are subject is very much less and the amount of outstanding deformation of the earth is correspondingly less than we could have reasonably expected. I have never supposed that isostasy was a force or condition which produced great elevations and subsidences of the earth. I^have always 40 HAYFORD been careful to distinguish sharply between the force which tends to preserve the various elevations and depressions of the earth from the force which tends to raise the lands and depress the sea bottoms. Those two classes of forces are at work independently of each other. The heavy masses of sediment which are formed upon the bottom of the sea can, I conceive, only be elevated by a positive uplifting force. Those portions of the land which are being denuded can only have their profiles depressed by an independent process of subsidence. Isostasy merely tends to keep the levels of the denuded region on the one hand, and the loaded regions of the sea bottom on the other, at constant levels. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 41-90. May iS, 1906. DISTRIBUTION OF THE LYMPHATICS IN THE HEAD, AND IN THE DORSAL, PECTORAL, AND VENTRAL FINS OF SCORP^N- ICHTHYS MARMORATUS. By Wm. F. Allen. CONTENTS. Page. Introduction 41 General Survey of the Lymphatics of Scorpienichthys 44 Superficial or Subcutaneous Lymphatics of the Trunk 47 Profundus or Submuscular Lymphatics of the Trunk 58 Facial Lymphatics 65 Lymphatics of the Hyoid Arch 66 Cephalic Sinus • 67 Pericardial Sinuses 71 General Considerations and Summary 78 Synonymy 83 Literature S4 Description of the Figures 87 Abbreviations Used in the Figures 87 I. INTRODUCTION. In some previous work on the Blood-Vascular System of the Loricati (2)1 the lymphatics were frequently injected to distin- guish them from the veins, and, and upon looking over the lit- erature of the lymphatics of fishes, I was impressed with the general incompleteness and obscureness that seemed to charac- terize it. Ophiodon and Scorpcenichthys differ very materially 1 The figures in parentheses refer to a list of the literature at the end of the paper. Proc. Wash. Acad. Sci., May, 1906. 41 42 ALLEN in many important details from the forms that have already- been studied, namely : Squalus, Raja, Torpedo, Amia ( = Amiatus), Cyprinus, Leuciscus, Salmo, Lucius (= Esox), Pe?'ca, Lophius, Pleuronectes and Uranoscopus . The lym- phatics of the Loricati therefore appealed to me as a subject worthy of study ; hence this paper, which deals with the distri- bution of the lymphatic vessels in the head, dorsal, and paired fins of Scorpainichthys. Two investigators of this subject in selachians, namely, Robin (23) and Mayer (18) deny the existence of lymphatics in fishes other than the visceral system. They consider the super- ficial and profundus vessels of the head and trunk as veins, and their sinuses they regard as venous sinuses. If this is true for selachians, it is certainly not true for the teleosts. In Scorpceuichthys wherever there are blood-vessels and con- nective tissue there are lymphatics. Strange to say, the lymph and the plasma of the blood of this group has a green- ish tinge, so that in an uninjected specimen the lymphatics, although lighter in color, might readily be taken for veins. Lymph usually contains some red corpuscles, often sufficient to give it a red tinge. Whether they have come directly into the lymphatics through the spleen and lymphatic glands, or through venous-lymphatic openings, or have transuded through the walls of the blood-vessels into lymphatic spaces and thence into the lymphatic vessels is still an open question. If, however, some lymph be drawn out with a pipette from the myelonal or superior longitudinal spinal lymphatic trunk, lying in the spinal canal above the cord, or from any of the lymphatic sinuses, and ejected into a bottle, and some blood be placed in a second bottle, the difference can quickly be detected upon the addition of a little alcohol. Most of the corpuscles of the lymph are color- less, while those of the blood have a dark brown color. The entire visceral lymphatic system can often be injected from the myelonal lymphatic trunk, which would hardly be possible were it a vein ; and further, the arrangement of what has been desig- nated as the neural lymphatic vessels, goes to prove that they are a part of a distinct profundis system. In front of each neu- ral spine there is a neural lymphatic vessel, which empties into DISTRIBUTION OF LYMPHATICS IN SCORP/ENICHTHYS 43 the myelonal lymphatic trunk ; also in front of each alternate neural spine there is a neural artery, coming from the dorsal aorta, and in front of the other alternate neural spines, a vein that empties either into the kidney or into the caudal vein. If the neural lymphatic vessels be regarded as veins, there would be one artery and vein in front of one set of alternate neural spines and two veins in front of the other set of alternate neural spines, a very unlikely arrangement. The same correlation can be shown in connection with the haemal vessels. Scor^pcenichthy s sometimes reaches a weight of twenty-five pounds and is one of the largest, if not the largest, of the Cot- tidae. It is easily obtained close to shore, is little used as food, lives out of water for hours, remains hard sometime after death, and taken all in all, furnishes a most excellent fish for anatom- ical study. These observations were made at the Hopkins Sea- side Laboratory, Pacific Grove, California. The same injecting masses were used that were employed in my studies on the blood vessels (2), and if only the lymphatics were to be injected preference was given to the berlin blue gelatin mass. The fish was severed transversely a little behind the vent and the body was placed head downward in a dish. A glass cannula connected with a piece of rubber tubing was forced forward in the myelonal lymphatic trunk. Usually a little cotton was placed around the cannula and over the cut ends of the dorsal, lateral, and ventral longitudinal lymphatic vessels. The syringe filled with the berlin blue mass was then connected with the rubber tubing, and with slow steady stroke the mass was forced into the lymphatics until they were com- pletely filled, which is usually the case, but should this fail en- tirely or in part, it can be repeated farther forward, or the lateral and ventral lymphatics can be injected in a similar manner. In other species of fishes having a very small myelonal vessel or none at all, one has to resort mainly to the lateral lymphatic trunks. The tail can be injected caudad in a similar manner from the myelonal lymphatic trunk. It is, however, of primary importance in working with fishes that have been caught with a hook to cut the line if the hook has been swallowed. To at- tempt pulling it out would, in all probability, rupture the large 44 ALLEN sinuses surrounding the heart, which would be fatal to a suc- cessful injection. The history of the work done on the lymphatics has been given by Milne-Edwards (16), Robin (23), Trois (28), and Hop- kins (8). The general physiology and physiological history is fully set forth in Schafer (26). A recent paper of unusual in- terest is that of F. M. Sabin's " On the Origin of the Lymphatic System from the Veins and the Development of the Lymph Hearts and Thoracic Duct in the Pig" (27). Anything further on the history of the lymphatics of Pisces would be simply repetition. 2. GENERAL SURVEY OF THE LYMPHATICS OF SCORP^ENICHTHYS. As in the higher vertebrates, Milne-Edwards (16; p. 471-2) and subsequent investigators, have separated the lymphatics of fishes into a visceral and a muscular portion, the latter division having been further subdivided into a superficial or subcutaneous and a profundus or submuscular system. These three systems in Scorficenichthys are in close connection. Except in the head region the principal superficial and profundus vessels are longi- tudinal trunks that terminate anteriorly in the cephalic and peri- cardial sinuses, which empty into the jugular near the prootic process and into one of the branches of the inferior jugular ; posteriorly they are collected in the neighborhood of the last vertebra by the right and left forks of the caudal vein. The superficial or subcutaneous system of the trunk consists of 4 longitudinal canals, respectively — dorsal, ventral, and lateral. Both of the lateral lymphatic trunks (Figs. 1, 4, 5 and 6; JL.L.V.) lie in a median plane, directly beneath the skin in a sheath of connective tissue that separates the dorsal from the ventral myotomes. Posteriorly they unite with the corres- ponding forks of the myelonal lymphatic trunk in the region of the last vertebra, and the combined trunks empty into the right and left branches of the caudal vein. Anteriorly after passing under the shoulder-girdle each of these trunks bifurcates, the lower fork emptying into the pericardial sinus, and the upper after receiving the corresponding fork of the myelonal lymphatic trunk, finally terminates in the cephalic sinus situated under DISTRIBUTION OF LYMPHATICS IN SCORP^ENICHTHYS 45 the hyomandibular bone. Throughout its entire course the lateral lymphatic trunk receives numerous dorsal and ventral intermuscular or transverse vessels, which arise from a network on the surface of the myotomes, and which anastomose with the dorsal and ventral lymphatic trunks. The dorsal lymphatic trunk (Figs. I and 4 ; D.L.V.) is found under the skin in the dorso-median line, but for the most part it is a paired vessel, running along on each side of the dorsal fin between the super- ficial and profundus dorsal fin muscles. In the region of the fins both trunks receive numerous cross-branches from the dorsal fin or median dorsal lymphatic vessel, that traverses the basal canal ' of the rays, and which collects the network from the dorsal fin. Throughout their whole length the dorsal lymphatic trunks are in connection with the intermuscular and the neural or interspinal vessels. Posteriorly this trunk is continued into the basal canal of the caudal fin as the caudal fin sinus, and when the median line is reached, unites with the corresponding ventral trunk in forming the hcemal or inferior spinal lymphatic canal. The ventral lymphatic trunk (Figs. 1, 2, 3, 4 and 6; V.L. V.) occupies a similar position on the lower side of the body. In the region of the anal fin it is a paired vessel. Be- tween the ventrals it expands into a reservoir, which receives the ventral fin sinuses that collect the lymph from the ventral fins. A few myotomes in advance of the ventrals it pierces the ventral fin musculature and follows along the lower side of the pelvics to empty into the pericardial sinus. Posteriorly it enters the basal canal of the caudal fin as the caudal fin sinus, and as described above anastomoses with the dorsal and haemal trunks. Throughout its entire course it is in connection with the ventral intermuscular or transverse vessels and the hcemal or interspinal lymphatic vessels. The most cephalic of the ventral inter- muscular vessels is much larger than the others and is desig- nated as the pectoral sinus (Figs. 1, 2, 3, 4, 5 and 6, P.S.). It receives the common trunk formed by the union of the 2 large sinuses situated on either side and at the base of the pec- 1 Immediately distad to the basal articulation of each raj there is a sort of for- amen, here designated as the basal foramen of the fin or the fin-ray. Trois calls it cruna (eye of a needle). 46 ALLEN toral fin, and each of these sinuses is in communication with cross-branches from the median pectoral fin sinus, lying within the basal canal and collecting the pectoral fin network. Two principal trunks constitute the main profundus or sub- muscular system. The dorsal one, which is undoubtedly the largest and most important vessel in Scorpamichlhys, is desig- nated as the my clonal or superior longitudinal lymphatic trunk (Figs. 4 and 5, My.L. V.). It runs in the spinal canal directly above the cord from which it is separated by a septum. Be- tween the skull and atlas it divides, and both forks after passing laterad out of this canal unite with the lateral lymphatic trunks in forming two common vesicles that finally terminate in their respective cephalic sinuses. In the region of the last vertebra this trunk again bifurcates to unite with the lateral trunks in forming joint papillae that undoubtedly empty into the right and left forks of the caudal vein. Along its entire course it receives numerous neural or interspinal vessels that communicate above with the dorsal trunk, and which are often prolonged ventrally to unite with the longitudinal haemal or inferior spinal lymphatic trunk and the abdominal sinus. Since the longitudinal hcemal or inferior spinal lymphatic trunk does not come under the head of this paper it has not been figured. It travels in the haemal canal, is continuous posteriorly with the dorsal and ventral trunks, and anteriorly it appears to empty into the abdominal sinus. Within the haemal canal it receives the haemal or inter- spinal vessels, which are also in communication with the ven- tral lymphatic trunk. The abdominal sinus (Figs. 4, 5 and 6, Abd.S.), which lies directly under the kidney and empties anteriorly into the cephalic and pericardial sinuses, receives nu- merous small lymphatic vessels from the reproductive organs, the great lymphatic trunk from the viscera, and many inter- costal vessels that are also connected with the profundus ven- tral lymphatic trunk. The latter vessel (Figs. 4, 6 and 9, V.L. V. 1 ) perhaps should have been included as one of the prin- cipal profundus longitudinal trunks. It pursues a similar course to the ventral lymphatic trunk along the lower wall of the visceral cavity and terminates anteriorly in the posterior end of the peri- cardial sinus. Several interlinking vessels were noticed in the DISTRIBUTION OF LYMPHATICS IN SCORIVEMCIITHYS 47 region of the ventral fins between this trunk and the main ven- tral lymphatic trunk. In the head region there is the same division into superficial and profundus systems. The superficial facial trunk (Figs. 4 and 5, S.Fac.L. V.) takes its origin in the neighborhood of the snout, and following along the upper inner edge of the sub- orbital bones, crosses the prootic process to join the jugular papilla of the cephalic sinus. The profundus facial trunk (Figs. 4 and 5, P.Kac.L.V.) could only be found in the orbit; branches were seen to enter it from the adductor mandibular muscles, and it was traced to a point in front of the prootic foramen, where it probably passed under the jugular and entered the abdominal sinus. This point, however, could not be deter- mined. There are 2 hyoidean lymphatic trunks, which run along the upper and lower sides of the arch (Figs. 3 and 4, A.Hyo. T. and P.Ilyo. T.). Of the 2 the lower is the principal stem. It collects the lymph from the branchiostegal region, and after receiving the upper vessel expands into a sinus that empties into the cephalic sinus. With Scorpamichlhys nothing has been done in connection with the lymphatics of the viscera. The main trunk, however, was often injected from the myelonal trunk, and was seen to follow the coeliaco-mesenteric artery and empty into the ab- dominal sinus. The lymph from the reproductive organs was poured into the abdominal sinus through numerous small vessels. In an injected specimen of Ophiodon lymphatic vessels were seen to arise from all the organs and empty into trunks that fol- lowed the courses of their corresponding blood-vessels, often nearly surrounding them. These canals were collected ante- riorly into a main coeliaco-mesenteric trunk that discharged itself in the abdominal sinus, and posteriorly the principal intestinal vessels traveled along with the posterior mesenteric vein between the reproductive organs to culminate in the abdominal sinus. 3. SUPERFICIAL OR SUBCUTANEOUS LYMPHATICS OF THE TRUNK. Lateral lymphatic trunk (Figs. 1, 4, 5 and 6, L.L. V.). — No other of the lymphatic canals of fishes has received the 48 ALLEN attention that this one has. It is easily located and the one from which this system has usually been injected. According to Milne-Edwards (16, p. 473) and Stannius (24, p. 254) this vessel was briefly described and its connection with the ductus of Cuvier noted by Hewson (5) and Monro (14). Vogt (33) however, was the first to show the connection of this trunk with the caudal vein, but (in 1, p. 134) gives the credit of this dis- covery to Hyrtl. From the latter (7) one obtains a most excel- lent account of this vessel. It is represented (p. 233) as arising from numerous dorsal and ventral transverse vessels (Seitenast- Parre) into which empty numerous smaller branches that collect the network coming from the matrix of the scales, and in con- versely restating the course of these vessels he says that the longitudinal trunk empties into the blood-vascular system. Further on (p. 234) he adds that in a successful injection the sinuses at the base of the pectoral and ventral fins and their branches were filled, but that no vessels were noted in connection with the dorsal fins. He also states that the lateral trunk ter- minates in a caudal sinus which empties into the caudal vein, and with Acipenser, Cyprinus, Leiiciscus, Esox and Gobio it ends anteriorly in a thin-walled pear-shaped cephalic sinus situated at the side of the skull directly behind the orbit, which empties into the jugular a little forward of the lower jaw and opercular vein. Shortly before the lateral lymphatic trunk terminates in the cephalic sinus several vessels coming from the jaws, the gills, the tongue and branchiostegal membrane are described as emptying into it. With the salmon and the trout, Hyrtl notes an entirely different anterior mode of communication with the venous system. Here the lateral trunk after curving under the clavicle empties into the sinus of the spermatic vein (Sinus der Holvenen) at its junction with the ductus of Cuvier, and this opening is guarded by a valve opening into the vein. While with Perca luciopei'ca, Tinea c/irysitis, and Cottus gobio both points of union are said to exist. Vogt (1, p. 134-7) also describes this trunk in the salmon with great detail. He noticed the transverse branches emptying into the main trunk, but con- sidered them as extravasations caused by the rupture of the thin-walled lateral canal. Posteriorly this canal is said to end DISTRIBUTION OF LYMPHATICS IN SCORP/ENICIITIIYS 49 in a sinus that empties into the caudal vein (veine cardinale). Upon reaching the end of the thoracic cavity it expands into a capacious reservoir, lying directly beneath the clavicle. Within the sinus there is a slit covered by a strong valve that leads into a vessel about the diameter of a pi»-head, which passes directly into the sinus of Cuvier. PI. K (Figs. 7 and 8 ; 64) shows this cephalic sinus papilla entering the sinus of Cuvier from the front. Vogt speaks of this trunk as a mucous canal, and since he could find no lateral mucous canal in the salmon into which the mucous pores emptied, he inferred that they emptied into this trunk. Stannius (24, p. 252-4) states that this trunk takes its source from numerous transverse branches, and following along with the truncus lateralis N. vagi terminates in caudal and cephalic sinuses. In addition the latter receives lymph from the head, gills, and trunk and empties into the precava (truncus transversus). From footnotes Milne-Edwards gives us the following additional information : Sihirus has three paral- lel lateral lymphatic vessels. With some fishes, as for example, the pike, roach, grudgeon, barb, and sturgeon, the lateral trunk is prolonged into the head and forms a sinus at the base of the skull, which empties into the jugular through a transverse canal. With the salmon, cod, rays, and sharks, the lateral trunks open into a pair of large cervical sinuses, that descend behind the center of the scapula and reunite in the median line at the point where the abdominal sinus joins them. Each of these scapular reservoirs communicates with the anterior vena cava or ductus Cuvieri through an orifice guarded by valves. Trois (28, 29, 30 and 31) gives a most excellent account of this vessel in Lo-phius -piscatoriuS) Uranoscofius scaber, and in several of the Pleuronectidas. He describes this trunk as ending in cephalic and caudal sinuses, and has satisfied himself that the transverse branches are not superfluous injecting mass as Vogt maintains. These vessels in Lophins are portrayed as sending off branches between the myotomes, which anastomose with similarly ar- ranged profundus vessels, forming a sort of ladder network. The transverse rami are represented as also anastomosing with the dorsal and ventral lymphatic trunks. Uranoscopus (29, p. 20, and PL on p. 37) furnishes a beautiful example of a fish 50 ALLEN having 3 longitudinal lateral lymphatic trunks, and since the middle one is the largest and is connected with the venous system at either end Trois is right in attributing only secondary importance to the other two. Trois also noted the knotty ap- pearance of the main lateral trunk in Uranoscofius (29, p. 21-2) which he thinks is due to rudimentary or imperfect valves that may have been put out of action by death, and the difficulty that he has experienced in injecting this trunk he ascribes to the resistance of these valves. This knotty appearance of the lateral trunk was also noticed in Scorficenichthys, but since no trace of valves has been found it seems best to attribute it to the outside resistance of the body musculature, rather than to the existence of hypothetical valves. To a considerable extent this arrange- ment may check the flow of the lymph and also the injecting mass, but by swelling out in the region of the centers of the myotomes it considerably increases the capacity of the lymphatic system. With the carp and pike Sappey (25, p. 41, and PI. XII, Fig. 2) describes and figures the lateral trunk as bending ventrad about 15 or 20 mm. in front of the clavicle and emptying directly into the jugular without forming any sinus. Hopkins (8, p. 371-2) in addition to describing the ordinary termination of the lateral trunk in cephalic and caudal sinuses says that in Am/a this trunk receives a branch from the pectoral sinus before pass- ing under the pectoral arch to open into the cephalic sinus, which is said to extend from the dorsal end of the clavicle to the base of the skull, and which empties into the jugular about 1 cm. cephalad and a little ventrad of the dorsal end of the clavicle. The lateral lymphatic trunk of Scorfiamichthys (Figs. 1, 4, 5 and 6, L..JL. V.) in the trunk region corresponds in the main with the descriptions of the previous investigators. As has already been stated in the general survey of the lymphatics this vessel lies beneath the skin in the median lateral line, and ex- cept in the cephalic portion of the trunk follows parallel, but mesad of the lateral line canal. It is distinctly a superficial vessel lying in the connective tissue septum that separates the two halves of the great lateral muscle. Throughout its entire course it takes up numerous dorsal and ventral intermuscular or trans- DISTRIBUTION OF LYMPHATICS IN SCO k I'.K \ K UTII YS 5 I verse branches, the most cephalic of which is a large ventral sinus to which the name pectoral sinus has been given. Pass- ing under the pectoral arch it follows along in front of the first rib across the anterior fork of the kidney. About half way across the kidney it receives a communication from the pericar- dial sinus (Figs. 4, 5 and 6, Per.S.), and when the atlas is reached unites with a fork of the myelonal or longitudinal spinal lymphatic trunk, the point of junction being marked by quite a large reservoir, designated as the occipital sinus (Figs. 4 and 5, Oc.S.). From here on the combined trunk thus formed is a distinct profundus vessel designated as the cranial lymphatic trunk (Figs. 4 and 5, Cr.L. V.). This vessel finally empties into the cephalic sinus, and is described in detail further on under a separate paragraph. Had the lateral trunk in Scorpcenichlhys, after having passed under the clavicle, curved downward without expanding into a sinus and emptied into the jugular, we would have the condi- tions as described for the carp and pike by Sappey (25). Had the lobe of the kidney not extended so far cephalad and the occipital sinus been located in front of the precava a little below its present position in Scorpcenichlhys, and received the branchial, hyoidean, and facial trunks, but not the myelonal, it would have answered to Vogt's description of the anterior termination of the lateral canal in the cephalic sinus with the salmon (1) ; provided that this sinus emptied into the precava. Finally, had the lateral trunk of Scorpcenichthys continued to the base of the skull, without receiving the myelonal trunk and the pericardial sinus, but collecting the branchial, facial and hyoidean trunks, and had sinus (s) emptied into the jugular we would have had the conditions met with in Cyprinus, Leuciscus, Esox, Acipen- ser, etc. It is of special interest to note in this connection that Hyrtl and Milne-Edwards have vaguely described 2 anterior communications from the lateral lymphatic trunk with the venous system in Cottus gobio, a species belonging to the same family as Scorpcenichthys . The intermuscular or transverse vessels (Figs. 1, 2, 4 and 5, Intm. V.) described by Hyrtl, Stannius, Milne-Edwards, Trois, Sappey, Hopkins, and which Vogt took to be extravasations of 52 ALLEX the injecting mass have certainly been found in Scorpcenichthys, following along superficially in the septa between the myotomes. The ventral vessels anastomose with the ventral lymphatic trunk and the dorsal with the dorsal trunk. These vessels are con- nected by a lymphatic network, which has its origin from the surface of the muscles and connective tissue, and branches are also received that arise from a very rich network on the subcuta- neous layer of the skin. This network is especially conspicuous in fresh-water drum, Aplodinotus grunniens, where it can be seen through the transparent scales. The secondary lateral trunks described by Trois in Uranoscopus are certainly of only secon- dary importance in Scorpcenichthys . For not only is the central vessel much larger and connected at either end with the venous system, but the secondary lateral vessels are only found in the cephalic end of the trunk, and the most dorsal one is not a con- tinuous trunk, but simply a series of regular cross vessels. Pectoral sinus and lymphatics of the pectoral Jin. — This sinus (Figs, i, 2, 3, 4, 5 and 6, P.S.) lies directly below the skin between the base of the pectoral fin and the post-clavicle, or perhaps to more accurately state it, between the superficial pec- toral adductor muscle, and the anterior myotomes and the sterno-hyoideus muscle (see fig. 2). In a well-injected speci- men it can be traced cephalad between the sterno-hyoideus and superficial abductor muscles to what has been designated as the ventral pericardial sinus (Figs. 3, 4 and 6, V.Per.S.). Since the ventral pericardial sinus receives the ventral lymphatic trunk, the union of the pectoral sinus with the ventral pericardial sinus is analogous to the union of the ventral intermuscular or trans- verse vessels with the ventral lymphatic trunk. In addition to its dorsal and ventral connections the pectoral sinus is always in direct communication with the abdominal sinus (Figs. 4 and 6, Abd.S.) In a very large specimen from which Fig. 6 was drawn an additional connection was also noticed with abdomi- nal sinus, which received a communicating branch from the pericardial sinus. Near the termination of the pectoral sinus in the lateral lymphatic trunk it receives a common trunk formed from the union of the outer and the inner pectoral fin sinuses (see figs. 1, 4 and 6). Of these two sinuses the inner is the DISTRIBUTION OF LYMPHATICS IN SCOK I'. 1. \ K IITII YS 53 larger (Figs, i, 2, ia and 4, I.P.S.). It follows along the base of the fin between the superficial and profundus adductor muscles, having blind sacs that pass between the profundus adductor muscles, but which send up short branches between the middle rays that soon fork to anastomose with the corres- ponding branches of its fellow, thus forming a circle over the bases of the middle rays (Fig. 2). These circular vessels re- ceive short pectoral-ray vessels (Figs. 2 and 2a, P.F.L. V. 0)), which run along the inner surface of the rays. They are much shorter than the main pectoral fin or pectoral fin-ray vessels, but appear in a well-injected specimen to have communicating branches with the main pectoral-ray vessels. The outer pec- toral sinus (Figs. 1 and 2a, O.P.S.) occupies a similar posi- tion between the superficial and profundus pectoral abductor muscles. It also sends back little pockets between the bundles of the profundus muscle, and receives dorsad a large branch that has its origin from the superficial and profundus abductor muscles (see Fig. 1). The outer pectoral sinus, after curving over the most dorsal ray, joins the inner pectoral sinus in form- ing a common trunk that empties into the main pectoral sinus. In addition to these 2 pectoral sinuses there is a third or median pectoral sinus (Fig. 2a, M.P.S.), which traverses the basal canal of the pectoral rays.1 This trunk receives the main pec- toral Jin or the main pectoral Jin-ray vessels (Figs. 2 and 2a, P.F.L. V.). Two such vessels accompany each ray and receive the network from the pectoral fin membrane. As is shown in Fig. 2a numerous cross-branches pass between the rays from the median pectoral sinus to both the inner and the outer pec- toral sinuses. Very little is to be found in the literature on the lymphatics of the pectoral fin. Hyrtl (7, p. 234) says that a pectoral sinus and its branches are filled in a successful injection of the lateral trunk. Stannius (24, p. 253) briefly describes a sinus at the base of the pectoral which receives numerous branches from the pectoral fin muscles. Hopkins simply states with Amia. (8, p. 371) that the lateral trunk receives the pectoral sinus. Trois (28, p. 8, and 29, p. 25) says that in Lophius and Uranoscopus 1 See note, page 45. 54 ALLEN there are at least 3 pectoral lymphatic trunks emptying into the cephalic sinus. Secondary branches are noted as anastomosing with the intercostals, and a sinus (vaso collettore) is spoken of as lying at the base of the rays and forming a ring about every ray. Lymphatic vessels are described as running along the surface of the rays and collecting the rich network from the skin. It will be seen from Trois' description that the lymphatics of the fin itself correspond somewhat with the arrangement in Scorpcenichthys, but as regards their mode of termination there is nothing in common. Dorsal lymphatic trunk (Figs. 1 and 4, D.L. V.). — Hyrtl and Vogt seem to have overlooked this canal. Stannius (24, p. 253) says that this trunk can be divided into 2 subordinate stems. First a vessel is described as running along the angle of the intermuscular septa, and a vessel is noted as passing along between the upper border of the great lateral muscle and the longitudinal muscle of the dorsal fin, which would place it at the base of the dorsal fin. Cross-branches are said to exist between the 2 trunks, and the second trunk receives numerous branches that followed along the rays. The first dorsal trunk of Stannius is undoubtedly the same as that de- scribed by Trois and myself as the most dorsal of the secondary lateral lymphatic trunks. Trois (28, p. 6) and Sappey (25, p. 47) describe the dorsal trunk in Lophius and the pike as a knotty vessel that separates into 3 distinct trunks upon reaching the dorsal fin, two of which run laterad to the base of the rays, while the third, more slender, passes through the holes in the base of the rays. Two vessels for each ray collect the lymph from the fin and empty into the median trunk. With Uranoscopus (29, p. 23) the anastomosis with the neural or interspinal vessels was noted. Hopkins (8, p. 373) describes this trunk in Amia as anastomosing with the lateral trunk before terminating in the caudal sinus, while anteriorly it bifurcates at the base of the skull, each fork emptying into a cephalic sinus. The description given of the dorsal longitudinal lymphatic trunk by Trois for Lophius and Uranoscopus will also answer very well for Scoj-pcenichthys. In the region of the dorsal fins this canal separates into three longitudinal trunks, two of which DISTRIBUTION OF LYMPHATICS IN SCORPvENICHTHYS 55 running along at the base of the fins between the great lateral, superficial, and profundus dorsal fin muscles are evidently the main stems, and might be designated as the lateral dorsal lym- phatic trunks (Figs. I and 4, D.L. V.) ; while the third or median dorsal lymphatic trunk (Figs. 1 and 4, D.L. V.w) simply passes through the basal canal of the rays and collects the dorsal fin lymphatic vessels. Numerous transverse inter- linking vessels were noticed between the median dorsal and the 2 lateral dorsal lymphatic trunks, and the dorsal Jin lym- phatic vessels (Figs. 1 and 4, D.F.L. V.) were merely small branches of the median lymphatic trunk, that followed along the cephalic and caudal surfaces of each spine and ray and col- lected the network from the fin membrane. Some variation, however, is shown in the anterior region of the first dorsal, where there is but one dorsal fin lymphatic vessel between the first and second, and between the second and third spines, both of which empty directly into the lateral dorsal trunks. In addi- tion to receiving the dorsal fin vessels the median dorsal lym- phatic trunk collects numerous small branches from the super- ficial or extrinsic dorsal fin muscles (Fig. 1). Anteriorly these 2 lateral dorsal lymphatic trunks do not terminate directly into cephalic sinus as described by Hopkins for Amia, but through- out their entire course communicate with the lateral lymphatic trunk through the intermuscular or transverse vessels, and with the myelonal or longitudinal spinal lymphatic trunk through the neural or interspinal vessels (Fig. 4, Neu.L. V.). The most ce- phalic neural or interspinal vessel (Figs. 4 and 5, JVeu.L. V.w) does not empty into the myelonal trunk, but follows along be- hind the skull and terminates in the cranial lymphatic trunk. Ventral lymphatic trunk and lymphatics of the ventral fins (Figs. 1, 2, 3, 4, 6, 9 and 10, l V.L.V.). — According to Milne-Edwards (16, p. 473) this vessel has been described by Monro (14) and Hewson (5) in Gadus, and as was the case with the dorsal trunk this canal seems to have been overlooked by Hyrtl and Vogt, although the former states that a ventral fin sinus is filled from a good injection of the lateral trunk. Stan- nius (24, p. 253) describes this vessel as unpaired, running 1 Figs. 7 to 10 are text-figs, on pp. 73, 74, 76 and 77. 56 ALLEN along between the halves of the lateral muscle from the vent to the shoulder-girdle. Caudad the vessel from the anal fin is dis- charged into it, and in the rump region it receives transverse vessels that follow the intermuscular septa. Trois (28, p. 7) and (29, p. 23) represents the ventral trunk in Lophius and Uranoscopus as consisting of 2 parallel trunks. With Urano- scopus they run close together and are connected by numerous cross-branches. In front of the anal they unite, and the com- mon trunk receives 3 vessels from the region of the anal fin, of which the median is the largest and traverses the basal canal of the rays ; the 2 lateral trunks are found at the base of the fin and travel toward the tail, and the 3 vessels are said to be con- nected by transverse rami. With Lophius we are told that the ventral canals bifurcate at a very acute angle in front of the ventral fins, and that these branches collect everything at the base of the ventrals. Sappey (25, p. 47) states with the pike and carp that this trunk is very similar to the dorsal ; that it is a single trunk in the region of the anal fin; but in advance of this, between the ventrals and pectorals, it consists of two par- allel trunks, which are prolonged to the posterior end of the skull. With the Pleuronectidse, Sappey (p. 49 and PI. XII, fig. 4) represents the ventral trunk as consisting of 2 parallel vessels in the region of the anal fin, but uniting in front of it in a common trunk that empties into the sinus of Cuvier. Hopkins (8, p. 372) describes the ventral trunk as beginning at the base of the caudal fin and extending cephalad to the heart, where it divides into two branches that merge into peri- cardial sinus, which communicates with the cephalic sinus and thence with the veins. On its course it receives the lymph from the anal and pectoral fins, and the sinus at the base of each of these is said to be much smaller than the one at the base of the pectoral. The ventral longitudinal lymphatic trunk of Scorpcenichthys (Figs. 1, 2, 3, 4, 6, and 9, V.L. V.) differs very materially from any of the species described above, although perhaps con- forming more closely to Hopkins' account for Anita than any of the others. The course of this trunk through the anal fin and its prolongation into the basal canal of the caudal fin is left DISTRIBUTION OF LYMPHATICS IN SCORP^ENICHTHYS 57 for another paper. In contrast to Trois' description this is a single trunk in Scorjxznichthys, extending from the vent to the origin of the pectoral fins. It runs along superficially in the ventro-median line from the vent to the origin of the pectorals, but pierces the body wall some distance behind its cephalic end ; the exact position is noted by 7'(Figs. I and 4), which is a little cephalad to the point of union with the vessels coming from between the profundus and superficial abductor muscles of the ventral fin. At this point a slight sinus is formed, which might be described as receiving an anterior and a posterior ventral trunk. The combined trunk or main stem thus formed penetrates obliquely between the 2 ventral fin abductor muscles, continues cephalad in a median line along the lower surface of the pelvic bones (Fig. 4), and passing between the clavicles and the pelvics, curves around the anterior end of the pelvics to enter the ventral -pericardial sinus (Figs. 4, 6, 9 and 10, V.JPer.S.) directly below the ventricle from the rear. The con- nection of this sinus with the veins will be described further on under a separate paragraph. Between the ventral fins the ventral trunk expands into a distinct pear-shaped sinus to which the name ventral sinus has been given (Figs. 1, 2 and 4, V.L.S.). This sinus receives at least one pair of intermuscular vessels and two ventral Jin sinuses (Figs. 1, 2 and 4, V.F.L. S.), which lie on the upper or inner base of the ventral fins. They receive the ventral Jin or the ventral Jin ray vessels (Figs. 1, 2 and 4, V.F.L. V.) from between each two rays, which soon bifurcate, each fork running along the adjoining rays and receiving the network from the membrane between the two. This is the typical arrangement, but some irregularities are often found as shown by Fig. 2, where some auxiliary ventral -fin vessels (Fig. 2, V.F.L. V. (1)) were noticed traversing the innermost rays, which reunited in a common vessel that passed over the lowrer side of the fin to empty into the ventral fin sinus close to its union with the ventral sinus. The ventral fin sinuses are prolonged cephalad between the external ventral fin abduc- tor muscles and the great lateral muscle as the ventral Jin muscu- lature lymphatic vessels (Figs. 1 and 2, V.M.L. V.)> and in route receive at least three intermuscular or transverse lymphatic Proc. Wash. Acad. Sci., May, 1906. 58 ALLEN vessels. Mesad of these ventral fin musculature lymphatic ves- sels there are still two other ventral fin musculature vessels (Fig. 2, V.M.L. V.w), which run between the internal and external ventral fin abductor muscles, and unite with the main ventral trunk immediately before it penetrates the musculature to empty into the pericardial sinus. From the above description of the termination of the ventral fin vessels into a single sinus outside the fin it will be noticed that this is a very different arrangement from that found in the dorsal and pectoral, where these vessels emptied into a median sinus, which traversed the basal canal of the rays, and having numerous transverse branches, communicating with the two lateral sinuses, lying at the base of the fin. In the paragraph on the lateral lymphatic trunk it was stated that a typical ventral intermuscular or transverse lymphatic vessel connected the lateral with the ventral lymphatic trunk. The most cephalic of these vessels, however, show some devia- tion from this general plan. The first one connects the pectoral sinus with the anterior end of the ventral trunk ; the second interlinks the pectoral sinus with the ventral fin intermuscular vessel ; the third and fourth communicate with the lateral trunk and the ventral fin intermuscular vessel ; the fifth unites with the lateral trunk and the ventral fin sinus ; while the sixth ex- tends from the lateral trunk to the ventral sinus. 4. PROFUNDUS LYMPHATICS OF THE TRUNK. The profundus ventral lymphatic tru?ik (Figs. 3 and 4, V.L. V.(1)), which seems to have escaped the notice of the pre- vious investigators, pursues a parallel and somewhat similar course to the main ventral tymphatic trunk between the great lateral muscles, but follows along the inner or visceral side of them. So far as could be ascertained it arose near the vent and passing cephalad along the median line close to the visceral cavity, terminated in the posterior end of one of the pericardial sinuses (Figs. 4, 6 and 9). Throughout its course it receives or gives off numerous intercostal lymphatic vessels (not shown in any of the figures), which follow along the inner side of the intermuscular septa, parallel with the intermuscular or trans- DISTRIBUTION OF LYMPHATICS IN SCORP/ENICIITHYS 59 verse lymphatic vessels and anastomose dorsally with the ab- dominal sinus. In the region of the ventral fin, and not improb- ably in other places, interlinking vessels were found between the profundus and superficial ventral trunks. Myelonal or superior longitudinal spinal lymphatic trunk (Figs. 4 and 5, My.L. V.). — This trunk with its neural or inter- spinal branches has been described by Hyrtl (7) and Stannius (24) as ending in the caudal sinus, but nothing whatever is said about its anterior connections. Trois states that this trunk in Lophius, Uranoscopus, and the Pleuronectidae (28 to 31) runs along in the spinal canal, receives numerous interspinal branches, and is connected with the haemal longitudinal trunks by means of transverse vessels. With Rhombus maximus and R. Icevis (30, p. 43) an additional longitudinal trunk was described as travel- ing along at the level of the bases of the interspinal bones. So far as could be discovered, Sappey (25) is the only one to give a cephalic ending for this canal. He states that it is a very important trunk with the pike and flatfish, and with these 2 fishes it is represented as extending from the coccyx of the last vertebra to the first cervical vertebra — where it turns to empty into the jugular. He further adds that there appears to be no caudal connection with the papilla of the lateral canal. No such trunk was portrayed by Vogt in the salmon or by Hop- kins in Amia. In Scorpamichthys the myelonal or super for longitudinal spinal lymphatic trunk (Figs. 4 and 5, My.L. V.) agrees very well with the descriptions given it by Trois and Sappey in Lophius, Uranoscopus, Esox, and the Pleuronectidee, except that its cephalic termination is very different from what Sappey repre- sents it for the pike and the flatfish. This trunk seems to be of different relative importance in different groups. With Scor- pcenichthys it is the longest and undoubtedly the most important of the longitudinal canals. It is located in the spinal canal directly above the myelon or cord, from which it is separated by a rather tough connective tissue septum. The neural ox inter- spinal lymphatic vessels (Fig. 4, Neu.L. V.), which have been described so accurately by Trois and Sappey, are very important branches of the myelonal trunk in Scorpcenichthys. Their 60 ALLEN course lies between the neural spines and anastomose dorsad with the dorsal or the 2 lateral dorsal lymphatic trunks. Since there is no special anterior connection of the dorsal lymphatic trunk with cephalic or pericardial sinus in Scorpcenichthys save through the neural or interspinal and the dorsal intermuscular or transverse vessels into the lateral or myelon trunks, and since the neural or interspinal vessels are much the larger, especially at the junction with the myelonal trunk, it is more than likely that they convey most of the lymph from the anterior portion of the dorsal fin region, while the main supply for the dorsal inter- muscular vessels evidently comes from the surface of the myo- tomes and the surrounding connective tissue. The main mye- lonal trunk extends from the last caudal vertebra to the skull. Its posterior connection with the caudal vein will be described in a later paper. When the skull is reached it bifurcates, each fork after passing laterad between the skull and the first vertebra or atlas empties into a rather large sinus situated at the side of the atlas, directly in front and a little below the base of the first rib. This sinus is designated as the occipital sinus (Figs. 4 and 5, Oc.S.) and receives, as has already been stated, the main lateral lymphatic trunk from the side and rear. Very likely this sinus should be considered nothing more than a swelling caused by the union of these 2 important trunks the resultant of which is the cranial lymphatic trunk. The course of this sinus-like vessel (Figs. 4 and 5, Cr.L. V.) is along the lateral base of the skull. Following the upper sur- face of the head kidney for a short distance, it crosses under the first spinal nerve and receives from above the Jirst neural or interspinal lymphatic vessel (Figs. 4 and 5, Neu.L. V.{1^) ; then continuing along the side of the cranial wall between the great abdominal lymphatic sinus and the IX and X cranial nerves expands into a sinus (Figs. 4 and 5, S.), which lies directly above the jugular vein, on a level with the optic lobes, immedi- ately behind the prootic process and between the skull and the first internal branchial levator muscle. This sinus has 2 open- ings ; the most cephalic one is simply a tapering down of the sinus into a papilla, which curves outward and downward to communicate with the abdominal sinus ; while the other opening DISTRIBUTION OF LYMPHATICS IN SCORP^NICHTHYS 6 1 leads into a lateral vessel or papilla, which curves around the first internal branchial levator muscle to empty into what has been designated as the cephalic sinus (Figs. 4 and 5, Ceph.S.). A full description of this sinus and its connection with the jugu- lar behind the prootic process will be given under a separate paragraph. Longitudinal /nrmal or inferior spinal lymphatic trunk and the abdominal sinus. — Hyrtl and Stannius seemed to have over- looked these vessels, but such a canal is represented by Vogt (1, p. 138) as consisting of 2 large lymphatic trunks that follow the aorta, and into which the trunk from the viscera and the vessels from the body wall empty. The posterior connections of these trunks were not given, but anteriorly they are said to empty into a branch of the third canal, terminating in the cephalic sinus. Vogt states (p. 138) that this canal (PL L, Figs. 1 and 8 ; 64) comes from a common reservoir which fol- lows the superior plate of the fourth branchial arch, and that it receives 2 important branches, one coming from the fourth branchial arch and the other arising at the middle of the body. The last branch is said to communicate in the median line with the corresponding branch from the opposite side immediately in front of the kidney, and at this point receives the 2 longitudinal trunks which follow the aorta. Two small vessels, which could not be definitely traced, but which appeared to come from the brain, are described as emptying into the cephalic ends of these longitudinal trunks. Milne-Edwards (16, p. 477) says that in general there are 2 lymphatic canals running parallel with the aorta, but expresses some doubt about their emptying into the cervical or cephalic sinuses. He further adds in a footnote that Fohmann (4) found 2 longitudinal lymphatic vessels traveling along with the aorta in the eel, which received branches from the trunk musculature and emptied anteriorly into the cephalic sinus. With the pike Sappey (25, p. 49) represents the trunk sous-vertebral 2,$ occupying the same canal as the caudal artery and vein, being situated below the vein, and receiving branches which traverse the muscles adjacent to the hasmal spines. With the Pleuronectidee (p. 50) he states that the inferior spinal trunk empties into the jugular directly below the superior trunk. It 62 ALLEN is also of interest to note in this connection that he claims to have found the minute lymphatic vessels anastomosing with the blood capillaries in the connective tissue of the muscles and the skin. Trois' description of this canal in Lofhius, Urano- scofius, and in the Pleuronectidae (28 to 31) is very similar to Sappey's, but so far as could be learned he does not give a cephalic ending for this trunk. With the Pleuronectidas he finds 2 parallel longitudinal vessels, a superior and an inferior longi- tudinal trunk, having numerous anastomosing cross branches that form a scale-shaped network on the caudal vein. Hopkins does not mention any longitudinal haemal trunk, but describes (8, p. 375) a large abdominal sinus running along the right side of the air-bladder. Caudad it is said to anastomose with one of the ducts from the duodenum ; throughout its course it receives branches from the bladder and the stomach and finally empties into the right lymphatic sinus, which terminates in the ductus Cuvieri. Both the longitudinal haemal lymphatic trunk and the abdom- inal sinus were found in Scor^pcenichthys. The haemal trunk was noticed only in the caudal region, and undoubtedly empties into the abdomidal sinus. The abdominal sinus in Scoi'-panichthys (Figs. 4, 5 and 6, Abd.S.) is a very large and important sinus, lying directly below the kidney and extending from the posterior end of the abdominal cavity to the orbit. A little behind the precava it divides, each fork following along under its respective lobe of the kidney continues cephalad along the ventro-lateral surface of the skull, and when the prootic process is reached directly below the jugular, or directly opposite the first internal branchial levator muscle, it turns inward and downward to end blindly opposite the parasphenoid behind the orbit. In some specimens the injecting mass so settled as to give the appearance of 2 abdominal sinuses with numerous cross branches in the visceral cavity. Throughout the abdominal cavity this sinus receives many branches from the reproductive organs, urinary bladder, body wall, and probably from the kidney itself. The body wall vessels are the intercostals, which follow along the inner surface of the intermuscular septa and anastomose ventrad with DISTRIBUTION OF LYMPHATICS l\ SCORP^ENICHTHYS 63 the profundus ventral lymphatic vessel. Numerous interlinking vessels were also found between this sinus and the myelonal trunk. With Ophiodon a large posterior mesenteric trunk was seen to pass between the generative organs with the correspond- ing vein acid empty into this sinus ; it had its origin from the posterior end of the intestine, being simply a continuation of the main intestinal trunk. As has already been stated the abdomi- nal sinus receives a communication from the pectoral sinus, and a little in advance of this a connection is received from the peri- cardial sinus (Figs. 4 and 6) ; while between the two it receives the large cceliaco-mesenteric lymphatic trunk (Figs. 4 and 6, Cce. Mes. L. V.), coming from the viscera and following the course of the corresponding artery. In advance of the head kidney each cephalic fork of this sinus swells up considerably upon the receipt of 3 sinuses from the region of the branchial arches. An important communication, which has already been mentioned is the papilla from sinus (S) of the cranial lymphatic trunk (Figs. 4 and 5, S.). Another possible accession is the profundus facial lymphatic trunk (Figs. 4 and 5, P.Fac. L. V.). Branchial or dorsal branchial sinuses (Figs. 4 and 5, Br.L.Si). These 3 sinuses appear to arise from the dorsal extremities of the first, second, third and fourth arches respectively, and pass- ing between the obliqui dorsales muscles, unite with each other and the abdominal sinus in such a way as to entirely encircle the 2 internal branchial levator muscles. My injections simply showed these sinuses to be blind pockets off from the ab- dominal sinus, and no trunks from the branchial arches or even from the dorsal branchial muscles were seen to empty into them. Vogt in the salmon (1, p. 177-8) describes the second canal emptying into the common cephalic sinus as being composed of 3 different branches, each of which is composed of 2 different components. These 3 branches come from the first, second, and third branchial arches, and of their 2 components, one is very small, arising from the superior part of the arch especially from the filaments ; while the other is more superficial, continues along the arch and unites with the inferior jugular (Veine de 64 ALLEN Duvernoy). Vogt states that he has succeeded in injecting the inferior jugular from the common branchial canal (Fig. L ; 63). A somewhat similar arrangement is shown for the fourth arch ; the two branchial components unite in a common stem that anas- tomoses with a large trunk coming from the middle <3f the body and finally ends in the cephalic sinus as described under the abdominal sinus. Stannius (24, p. 254) says that lymphatic vessels arise from the branchial arches and empty into a trunk running in the canal of the arches. Trois (28 and 29) always found a branchial trunk in the groove of each arch in Lo^phms and Uranoscoftus, which received branches arising from net- works in the arches and in the filaments. The filament net- works are represented as being much finer and necklace-shaped, while those of the arch are irregular and much coarser. In connection with Uranoscoptis (29, p. 26) the author states that Fohman (4) is the only one having described these branchial lymphatic vessels, and attributes the fact that they have not been discovered by other investigators to their faulty method of pro- cedure, namely, of immersing the specimen in alcohol.1 Miiller (15) and Stannius (24) have shown a somewhat similar arrangementof branchial vessels under the head of vencentitritice, and in a previous paper of mine (2) both dorsal and ventral nutrient branchial veins were figured and described ; the former emptied into the jugular and the latter into the inferior jugular. These vessels received branches from the arches and the filament nutrient veins, which arose from a capillary network in the fila- ments. This network could easily be distinguished from the regular gill network on account of its different arrangement and its much coarser meshes. In not being able to find lymphatic vessels arising from the gills and the branchial arches I am not disposed to contradict their existence, for I can see no reason why the gills should not possess lymphatics. 'In this connection, would state that I see no objection to preserving an Injected specimen in alcohol or formalin for future reference. I have kept injected material in formalin for years in as perfect shape as when first injected, and upon writing up a description find them of greater value than reference figures or mere memory. DISTRIBUTION OF LYMPHATICS IN SCORP/ENICIITHYS 65 5. FACIAL LYMPHATICS. As in the trunk region there is a distinct superficial and pro- fundus system. Strange to say Vogt (1, p. 137) is the only anatomist to have definitely described lymphatics arising from the facial region of Pisces. The first canal emptying into the cephalic sinus in the salmon is said to originate on the temporal (pterotic) crest from two trunks coming from the head. The first branch, which is somewhat similar to the vessel described below in Scorpa>nic]ithys as the profundus facial lymphatic trunk, has its source at the anterior angle of the nasal fossa, and passing through the orbit receives branches from the upper part of the face and head. The second branch, which is evi- dently analogous to the superficial facial trunk in Scorpamich- thys, is represented as following along under the suborbital bones and collecting numerous branches from the surface of the cheeks, of which the inferior maxillary vessel is the largest; this is said to run along in front of the preopercle from which it receives several branches. Hyrtl (7, p. 236) describes a swelling of the jugular at the entrance of the optic nerve into the orbit that is in communication with a similar bulb on the opposite side as the sinus ophthalmicus (Fig. 8, d), and this sinus he thinks receives the lymph from the head. In a pre- vious paper (2) a similar sinus-like vessel was described as cross- ing the eye muscle canal and connecting the 2 internal jugular veins ; but with Ophiodon there is no marked swelling of the jugulars at the junction with the connecting vessel, which is evidently nothing more than a venous sinus. Stannius (24, p. 254) claims that the connection of the head and trunk lymphatics has not yet been made clear. Superficial facial lymphatic trunk (Figs. 4 and 5, S.Fac- L. V.). — With Scorpatnichthys this trunk has its origin in the region of the first suborbital bone from a dorsal and a ventral fork ; the dorsal branch comes from the snout and the space surrounding the nasal sac ; while the ventral branch follows along above and behind the maxilla. After uniting the common stem crosses the orbit between the adductor muscle of the pala- tine arch and the upper and inner edge of the chain of subor- bital bones, or suborbital stay as it is in this species. Upon 66 ALLEN reaching the posterior end of the orbit it crosses over the facialis- mandibularis nerve and vein, and after passing across the lateral surface of the prootic process unites with the jugular papilla of the cephalic sinus (see Figs. 4 and 5) and ultimately reaches the jugular. Numerous branches were received from the sur- face of the adductor mandibular muscles, and soon after cross- ing the facialis-mandibularis vein, is joined from the rear by a rather large branch, which runs along the dorsal and inner surface of the opercle. No inferior maxillary branch as described by Vogt in the salmon was noticed. Profundus facial lymphatic trunk (Figs. 4 and 5, P.Fac- L. V.). — In the last specimen dissected the course of this canal could be followed much better than in any of the others. It appears to be entirely confined to the region of the orbit. In this specimen it started from the dorsal side of the orbit, and passing ventrad across the anterior end of the orbit bifurcates at the ventro-cephalic corner of the orbit, but soon reunites. The outer or sinus portion being much the larger, extends some dis- tance ventrad between the adductor muscles of the palatine arch and the mandible ; a few branches from the adductor mandibular were noticed, and after uniting the common stem passes caudad across the orbit on the surface of the adductor muscle of the palatine arch, a little mesad of the facialis-maxillaris vein, but some little distance inward from the superficial facial lymphatic vessel. This trunk could be traced to a point immediately be- neath the junction of the internal and external jugular veins, but no farther. Very likely it continues caudad below the jugular through the prootic process foramen and empties into the abdominal sinus. The final ending of the profundus facial lymphatic trunk could not, however, be determined. 6. LYMPHATICS OF THE HYOID ARCH. Two distinct lymphatic canals are found running along the dorsal or anterior and the ventral or posterior edges of the arch. Of these the -posterior or ventral lymphatic trunk (Figs. 3 and 4, P.Hyo. T.) appears to be the main stem. It traverses the lower and posterior edge of the epi- and cerato-hyals, and from be- tween each 2 branchiostegal rays receives 1 or 2 small branches DISTRIBUTION OF LYMPHATICS IN SCORPyENICHTHYS 67 (Fig- 3, Hh.S.L. V.) arising from the hyo-hyoideus superior muscles and the branchiostegal membrane. Directly behind the inter-hyal the posterior hyoidean trunk expands into a reservoir designated as the hyoidean sinus (Figs. 3 and 4, Ilyo.S.). This sinus also receives the anterior or dorsal hyoidean trunk (Figs. 3 and 4, A.Hyo.T.), which runs along the upper and anterior edge of the epi- and cerato-hyals, and in front of the inter-hyal swells up into a sort of a sinus from which a papilla crosses the outer surface of the inter-hyal and empties into the main hyoi- dean sinus. At about the center of the arch quite an important branch was seen to join it from the genio-hyoideus muscle. This vessel (Figs. 2 and 3, Gh.L. V.) after passing along the inner ventral surface of the muscle, crosses the first and second branchiostegal rays, and at this point makes a sharp curve to cross the outer surface of the cerato-hyal and empty into the anterior hyoidean trunk. The main hyoidean sinus (Fig. 4, Ilyo.S.) gradually tapers down dorsally into a papilla that empties into the cephalic sinus from below and to the rear, and ultimately reaches the jugular through it. This system of lymphatic vessels appears to have been almost entirely over- looked. The only reference found is that of Hyrtl (7, p. 237)» where he represents the lymphatics from the tongue and branchi- ostegal rays as emptying into the lateral trunk near the cephalic sinus. This concludes the description of the distribution of the lymphatic trunks of the head, dorsal, ventral and pectoral fins of Scorpcsnichthys, but 2 important sinuses into which they empty, and which ultimately terminate in the venous system remain to be described. 7. CEPHALIC SINUS. With the salmon Vogt (1, p. 136) represents the cephalic sinus as being an expansion of the lateral lymphatic trunk at the cephalic end of the thorax, which lies under the clavicle and has a slit covered by a valve that leads into a vessel about the diameter of a pin head, which terminates in the sinus of Cuvier near the jugular. This sinus is said to have 3 other openings that are also defended by valves. In brief the first comes from 68 ALLEN the face, the second from the first 3 branchial arches, and the third from the fourth branchial arch, the viscera, and the body wall. Hyrtl (7) states that the lateral trunk in Acificn- ser, Cy-prinns, Leuciscus, Esox, etc., ends in a thin-walled pear-shaped sinus situated at the side of the skull, a little behind the orbit, which empties into the jugular a little forward of the lower jaw and opercular vein. This sinus he believes is contractile upon electrical or mechanical stimulation. With the salmon and trout the lateral trunk is said after passing under the clavicle to end in a sinus that discharges itself in the sinus of the spermatic vein (Sinus der Holvenen) at its junction with the ductus of Cuvier. A valve was seen at the point of union, but no vessels were described in advance of the cephalic sinus ; doubtless for reasons so fully set forth by Vogt (1), namely, that the vessels emptying into this sinus were all guarded by valves, and the injection mass would naturally find its way into the venous system. With Pcrca lucioferca, Tinea chrysitis and Cottus gobio both points of union were noticed. Stannius (24, p. 254) speaks of the lymphatics from the head, gills, and trunk as uniting in a sinus that emptied into the truncus transversus (pre- cava) near the jugular, and in a footnote states that this com- munication was noted by Monro (14) and Hewson (5). Milne- Edwards (16, p. 475) following Hyrtl says that in the pike, roach, grudgeon, barb and sturgeon, the lateral trunk is pro- longed into the head and terminates at the base of the cranium into a sinus that empties into the jugular through a transverse canal. While in the salmon, cod, rays and sharks he describes the lateral vessels as opening into a pair of cervical sinuses, which descend behind the center of the scapula to unite in the median line at a point where the abdominal sinus joins them, and each of these scapular reservoirs is said to communicate with the ductus Cuvieri through an orifice protected by valves. Also with Perca lucioferca and Cottus Gobio 2 modes of com- munication with the venous system are vaguely mentioned. Trois's description in Lophius (28, p. 8) of the termination of the 2 lateral lymphatic vessels in the cervical or cephalic sinuses and their union with the abdominal sinus is almost identical with the descriptions given by Hyrtl and Milne-Edwards, DISTRIBUTION OF LYMPHATICS IN SCORP.-EMCIITIIYS 69 except that no connection is noted with the venous system. According to Sappey (25) there are no cephalic sinuses in the carp or the pike. He states that both the lateral and myelonal or superior longitudinal spinal lymphatic trunks empty directly into the jugular, and with the Pleuronectidie the inferior spinal or longitudinal hcemal trunk likewise terminates in the jugular, while the ventral trunk empties directly into the ductus Cuvieri. No other vessels were mentioned from the head region, doubt- less for the reasons given above. Hopkins represents the lat- eral lymphatic trunk of Aiuia (8, p. 371) as passing under the clavicle and opening into a cephalic sinus at the base of the cranium. This sinus is described as receiving the pericardial sinus from below ; its opening into the jugular is said to be about 1 cm. cephalad and a little ventrad of the dorsal end of the clavicle, and the orifice is guarded by a valve opening into the vein. Possibly it might simplify matters somewhat to classify the cephalic sinuses and their connections described in the previous paragraph under 5 different heads. Firsts in Acifienscr, Cy- ■prinus Leaciscus, Fsox, etc., the lateral trunk after passing under the pectoral arch follows the ramus lateralis vagi to the base of the skull, and there expands into a cephalic sinus that empties into the jugular. Second, with Lofhius, the salmon, trout, ray, and shark the lateral trunk immediately after pass- ing under the shoulder-girdle discharges itself in a cervical or cephalic sinus that empties into the precava, and which accord- ing to Vogt in the salmon receives other trunks from the face and the branchial arches. Third, midway between these two extremes comes Aw/a with a lateral trunk which after passing under the clavicle terminates in a cephalic sinus, that also re- ceives the pericardial sinus, and which ultimately empties into the jugular instead of the precava. Fourth, Perca, Tinea, and Cottus are vaguely described as having two communica- tions with the venous system ; probably the jugular and pre- cava connections are the ones referred to. Fifth, with the carp, pike and flatfish there are said to be no cephalic sinuses, the main lymphatic trunks emptying directly into the jugular and precava. 170 ALLEN What is designated as the cephalic sinus in Sco?'pceiiichthys (Figs. 4 and 5, Cefih.S.) does not fit very well into any of these classes and seems to constitute one of its own. Here this sinus is a sort of stomach-shaped reservoir situated between the hyomandibular bone and the first internal branchial levator mus- cle, which would make it nearly opposite and a little below the level of the cerebrum and the optic lobes. Its cephalic dorsal corner gradually tapers down into a papilla, which passes in- ward and empties into the jugular directly behind the prootic process. At this point the jugular itself expands into a sort of reservoir before greatly diminishing in caliber to pass through the foramen formed by the prootic bone and its process. In a large uninjected specimen of Ophiodon from which a portion of the dorsal wall of the jugular had been removed the orifice could be distinctly seen from the inside of the vein. It pierced the ventro-lateral wall a little behind the prootic process, and was guarded by a strong valve that opened into the vein. This valve was attached dorsad, but was free three fourths of the way around. As the cephalic sinus papilla passed behind the prootic process to empty into the jugular it recieves the super- ficial facial trunk. In the posterior ventral corner of the cephalic sinus there is a second opening into which a prolongation of the hyoidean sinus enters. A third opening remains to be noted in the posterior dorsal corner, which is in connection with a lateral papilla from a sinus at the cephalic end of the cranial lymphatic trunk (Figs. 4 and 5, S). As previously stated this sinus corres- ponds in position to the cephalic sinus described and figured by Hyrtl in Leuciscus, however, in Scorjicenichthys this sinus does not empty directly into the venous system ; anteriorly it tapers rapidly down into a papilla that passes ventrad between the cephalic sinus papilla and the first internal branchial levator muscle to communicate with the cephalic end of the abdominal sinus, but in no case was any direct connection noticed between it and the cephalic sinus, the cephalic sinus papilla, or the jug- ular vein. As stated above the connection of this sinus with the cephalic sinus comes from its lateral wall. Sinus S in Scorfce- nichthys (Figs. 4 and 5) is therefore to be regarded as simply an DISTRIBUTION OF LYMPHATICS IN SCORPyENICIITHYS 7 1 expansion of the cranial lymphatic trunk ; a trunk that is formed by the union of the lateral and myelonal canals. 8. PERICARDIAL SINUSES. Strange to say so far as could be determined Hopkins (8, p. 372—3) is the only one to describe such a sinus ; evidently it is absent in the other species studied or else it has been over, looked. The ventral lymphatic trunk in „ \111ia is represented as branching at the level of the heart ; each fork running between the pericardium and the tough fibrous partition separating the pericardial from the abdominal cavity, is said to merge into large pericardial sinuses that communicate with the sinuses of the lateral trunk (cephalic sinuses). With Scorpcenichthys this is a very large and extremely important sinus, and appears to be made up of several divisions or sub-reservoirs, which have for convenience been designated as the main pericardial, pos- terior, and ventral pericardial sinuses. One of the main pericardial sinuses (Figs. 4, 6, 9 and 10, Per.S.) is perhaps best shown in Fig. 6, which is drawn from a very large specimen that was well injected and hardened in formalin. It is a retort-shaped reservoir situated directly behind the precava or ductus of Cuvier. Its dorsal stem crosses the corresponding lobe of the kidney to unite with the main lateral trunk. In this specimen a branch was given off caudad at the base of the kidney which anastomosed with a branch of the pectoral sinus that emptied into the abdominal sinus. In no other specimen was this connection noticed, but a little below this level and in front there is always some communication with the abdominal sinus. Here a much larger branch is given off cephalad (Figs. 4 and 6) which soon expands into 3 large divisions (Fig. 6 ; a, b and c). The most anterior one (a) passes cephalad to terminate in the abdominal sinus directly behind the precava. The middle one (b), which is the largest of the 3, is a blind sac that extends ventrad directly behind the precava and rests on the dorsal surface of the sinus venosus. Without carefully dissecting out sinus (/;) it always has the appearance of emptying into the sinus venosus. I have, however, carefully dissected out this sinus in many specimens to make certain that 72 ALLEN there was no communication with the venous system here, and have satisfied myself in every case that this is simply a blind sac. The third division (c) is merely a much smaller blind sac, lying behind (b). At about this level the pericardial sinus receives a small lymphatic vessel from the side, which comes from the center of the clavicle (Figs. 4 and 6, C.L. V.). In this region it is important to avoid confusing the external subclavian and anterior gastric or oesophagus veins (Fig. 6, J?. Sub. V. and A. Gas. V.) with the lymphatics. The external subclavian vein crosses over the pericardial sinus and its divi- sions {a, b and c) to discharge itself in the precava ; while the anterior gastric veins pass under the pericardial sinus, but over its divisions (a, b and c) and likewise empty into the precava. There is always quite a prominence in the neighborhood of the anterior ventral corner of the pericardial sinus which extends outward and forward some little distance between the external and internal pharyngo-clavicularis muscles. From a lateral view what appears to be a separate posterior pericardial sinus (Figs. 4 and 6, Per.S.m) emptying into the main pericardial sinus is shown in a ventral view (Figs. 9 and 10, Pcr.S.(Y)) to be nothing more than a posterior continuation of the main pericardial sinus. Each of these so-called posterior pericardial sinuses or posterior continuations of the main peri- cardial sinuses passes at first ventrad behind the sinus venosus and ventricle, being separated from them only by the pericar- dium, and when the posterior ventral corner of the ventricle is reached curves backward at nearly right angles. At this point in about half of the specimens a connecting branch (Fig. 6 and 10, X) was given off cephalad to anastomose with a papilla of the ventral pericardial sinus (Figs. 6 and 10, P. V.Pcr.S.) that communicates with the main pericardial sinus. In an equal number of specimens connecting vessel (X) was absent (see Figs. 4 and 9), and possibly it should be noted that in these specimens the ventral pericardial sinus papilla always followed very close to the posterior portion of the main pericardial sinus. Both of the posterior pericardial sinuses or posterior portions of the main pericardial sinuses continue backward some little dis- tance, gradually increasing in size as they approach one another, DISTRIBUTION OF LYMPHATICS IN SCORIM5NICHTII YS 73 until finally they come into contact, but do not anastomose. Both of them end some little distance in advance of the ventral fins, and either may receive the profundus ventral lymphatic trunk. Ji.l.J.V. Mut.Kto Ph.L.V. Nixt.Vn V.P?r.S.(r> Lin. r. Fig. 7. Shows the branching of the ventral pericardial sinus to the pharynx region, especially to the bases of the first and second branchial arches and the thyroid gland. The anterior ventral pericardial sinus has been cut and turned forward from its natural position. Small Scorpcenichthys. Natural size. A list of the abbreviations used in text-figs. 7 to 10 will be found in a general list, p. 87, under 13. With Scorfcenichthys there is always a distinct and very im- portant ventral ^pericardial sinus (Figs. 3, 4, 6, 7, 9 and 10, V. Per. Si). Since there is always a marked depression in the region of the bulbus arteriosus this sinus might be said to con- sist of an anterior and a posterior portion. The posterior por- tion of this sinus (Figs. 3,4, 6, 9 and 10, V.Per.S.) is a somewhat irregularly-shaped reservoir situated below the anterior end of the ventricle and the bulbus arteriosus. Its 2 posterior dorsal corners are prolonged across the posterior half of the ventricle as papilla? (Figs. 4, 6, 9 and 10, P. V.Per.S.), which com- municate with the anterior ventral corners of the corresponding pericardial sinuses. Between these 2 papillae the ventral longi- tudinal lymphatic trunk curves around the cephalic ends of the pelvic bones, and empties in the median line into the posterior end of the ventral sinus. Ventrally this sinus bifurcates and soon forms 2 conspicuous reservoirs situated on the ventral sur- Proc. Wash. Acad. Sci., May, 1906. 74 ALLEN face of the clavicles (see Fig. 3), and into these sinuses the ven- tral prolongations of the pectoral sinuses terminate. The ante- rior dorsal corner of the posterior ventral pericardial sinus is con- tinuous with the anterior portion of the ventral pericardial sinus. Mut.m JVntVar .I.j.r. Fig. 8. Deeper dissection of the same specimen as Fig. 7 to show the origin of the inferior jugular from the nutrient branchial veins and its course above the ventral aorta. This sinus (Figs. 3, 4, 6, 7, 9 and 10, V.Per.S.{l)) passes cepha- lad along the lower side of the ventral aorta, and when midway between the combined trunks of the third and fourth afferent branchial vessels and the second pair of afferent branchial vessels, it divides ; each fork, designated as the ^pharynx lym- phatic vessel (Figs. 3, 6, 7 and 8, Ph.L.V.), passes at first obliquely across the thyroid gland and the second afferent branchial trunk. Here it bifurcates, the anterior fork going along the side of the thyroid to the base of the first branchial arch ; while the other stem continues along between the afferent and efferent branchial vessels of the second arch and shortly sends off a branch which traverses along behind the afferent branchial trunk. Neither of these branches could be traced farther than to the origin of the first branchial filaments. They evidently only receive lymph from the connective tissue lining the base of the second branchial arch and the thyroid gland. Since no similar branch was found on any of the other branchial arches this fork has been designated as a pharynx rather than a branchial vessel. In well-injected specimens as is shown by (Fig. 6, Thyr.L. V., and Fig. 3) there was found an additional DISTRIBUTION OF LYMPHATICS IN SCORIVENICHTHYS 75 stem emptying into the ventral pericardial sinus between the 2 pharynx vessels. It apparently arises solely from the thyroid gland, and it may have some direct connection with some of the branches of the inferior jugular that run along the dorsal sur- face of the gland. During the early stages of this work I had no inference that either the pharynx or the thyroid lymphatic vessels had any communication with the inferior jugular. Later on a specimen was dissected in which the entire venous system, with the single exception of the jugular and its branches, was found to be well filled from an injection of the myelonal lymphatic trunk. This of course led me to believe that there must be another commu- nication with the venous system in the head region other than the cephalic sinus, and most careful search was made of all the lymphatic vessels surrounding the jugular, precava, sinus venosus, and especially lobe (b) of the pericardial sinus ; still no connection whatever was found. Also every opening into these veins was accounted for. As the work progressed the lymphatics of several heads was injected from the ventral lymphatic trunk, and as a rule in these specimens the pericar- dial lymphatic sinuses, the thyroid, and pharynx lymphatic ves- sels were well filled, and the mass entered the nutrient branchial and the inferior jugular veins, but rarely extended in the inferior jugular as far back as the sinus venosus ; it would first run out some of the cut lymphatic vessels that were severed in removing the head. In one specimen I first injected the venous system from one of the hepatic veins with a blue mass, and after allow- ing the mass to partially solidify, injected the lymphatics with a yellow mass from the ventral lymphatic trunk. The lymphatic sinuses, pharynx, and thyroid lymphatic vessels were found to be well filled with the yellow mass, as was also the nutrient branchial veins, and the yellow mass had forced back the blue a short distance in the inferior jugular vein. Upon further dis- section the entire venous system, including the jugular and the dorsal nutrient branchial veins, was found to be filled with the blue mass, indicating of course that a connection must exist be- tween either the pharynx or the thyroid lymphatic vessel and one of the branches of the inferior jugular. By dissection I have 76 ALLEN been unable to find the exact point of union, but am inclined to believe that the thyroid vessel is the one that communicates with the venous system. For a short distance each pharynx lymphatic vessel runs along the ventral surface of the combined trunk of the third and fourth nutrient branchial veins, and at this point several dorsal branches are given off, but they ap- parently go to the posterior end of the thyroid. The largest of them, however, leads into the sinus situated at the base of the second branchial arch. H.LJ.V, V.Per.Slrr P. V.fkrS: Per.Sr Fig. 9. Ventral view of the large pericardial lymphatic sinuses surrounding the heart. Only a portion of the ventral pericardial sinus is figured. In this specimen the two interlinking arms between the ventral pericardial and the peri- cardial sinuses had no additional connection with the posterior portion of the pericardial sinus as it has in some specimens, shown in Fig. 10. Medium large Scorpcenichthys. Natural size. It is of interest in this connection to again note that Vogt (i, p. 138) in the salmon describes one of the 2 dorsal lymphatic trunks of each branchial arch*, which terminates in the cephalic sinus, as being prolonged ventrad and anastomosing with the veine de Duvernoy (inferior jugular), and from Vogt's descrip- tion it is perfectly clear that he has not confused the nutrient DISTRIBUTION OF LYMPHATICS IX SCORI'/ENTCHTHYS 77 branchial veins for lymphatics, otherwise they would terminate in the jugular and not in the lymphatic trunk that emptied into the cephalic sinus. It will be seen at a glance that this connec- tion of the dorsal lymphatic trunks with the inferior jugular described by Vogt in the salmon is very different from the some- what hypothetical union described above, notwithstanding that both modes of communication occur in the same vicinity. KPer.SAO &r.S. Per.&W Fig. io. Same view of another specimen as Fig. 9 in which the interlinking arms of the pericardial and ventral pericardial sinuses had an additional connec- tion (JC) with the posterior portion of the pericardial sinus. Medium size Scorpcznichthys. Natural size. Possibly at this point a note should be made in connection with the inferior jugular and its branches. In Scorfamichthys 2 inferior jugulars empty into the sinus venosus, a large right and a much smaller left inferior jugular (Figs. 3, 6, 7 and 8, 7?. and L.I.J. V.) ; both of which pass along, above and to the side of the ventral aorta, and unite in a common stem directly behind the common trunks of the third and fourth afferent branchial vessels. Perhaps it would have been more accurate to have conversely stated this arrangement by saying that the common stem of the inferior jugular bifurcated behind the com- raoji trunks of the third and fourth afferent branchial vessels, 78 ALLEN and each fork after passing along the side of the ventral aorta emptied into the sinus venosus. Following the common stem of the inferior jugular cephalad it will be seen from (Figs. 6, 7 and 8) that it may branch and each fork receive first the com- bined sinus-like trunk of the third and fourth nutrient branchial veins and then in succession the second and first nutrient branchial veins as shown by Fig. 8, Nut. V.(S4), etc.) or as was noticed in other specimens may expand into a broad sinus between the second and third branchial arches, which in like manner collects the nutrient branchial veins. In either case the anterior part of the inferior jugular in spreading out over the thyroid gland took on more the appearance of a lymphatic trunk than it did a vein. • 9. GENERAL CONSIDERATIONS AND SUMMARY. Scorficenichtkys has as complete a lymphatic system as is to be found in any vertebrate ; in general wherever there is con- nective tissue there are lymphatics. As in the higher Verte- brata there are distinct superficial and profundus systems. In the trunk region the main lymphatic canals are longitudinal trunks that terminate caudad in the caudal vein, and cephalad empty in one way or another into the cephalic and ventral peri- cardial sinuses, which ultimately reach the jugular and appa- rently the inferior jugular veins. These sinuses are simply non-contractile reservoirs in no way comparable to the lym- phatic hearts of the Batrachia. In the region covered by this paper no valves were found except at the orifice of the cephalic sinus papilla in the jugular. 1. The lateral lymphatic canal in the trunk region very closely resembles the descriptions already given for other species. Dorsal and ventral intermuscular or transverse branches were regularly received ; they arose from a network in the connective tissue of the myotomes and skin, and anasto- mosed above with the dorsal lymphatic trunk and below with the ventral trunk. In the anterior region of the trunk there are dorsal and ventral lateral lymphatic vessels, which are merely a series of longitudinal cross-branches, lying above and below the main lateral trunk, but which give additional support DISTRIBUTION OF LYMPHATICS IN SCORP/ENICHTHYS 79 to Trois' statement that similar longitudinal trunks in Urano- scofins are doubtless of only secondary importance. Before passing under the shoulder-girdle the lateral trunk receives a large pectoral sinus that collects the lymph from the pectoral fin region, and from here on its course and connections are very different from what has been described for any other fish. Following the first rib inward it receives a communication from the pericardial sinus, and opposite the atlas unites with a fork of the myelonal trunk in what is designated as the occipital sinus, from which the cranial trunk has its source. 2. A large and very important myelonal or superior longi- tudinal spinal lymphatic trunk is found traversing the spinal canal above the cord, from which it is separated by a septum. The neural or interspinal branches noted by previous workers are very conspicuous in Scorfcenichlhys ; all of which anasto- mose above with the dorsal lymphatic trunks, and many of them are prolonged ventrally to connect with the abdominal sinus or the longitudinal haemal lymphatic trunk. Evidently this trunk is absent in many species or else it has been over- looked. So far as could be ascertained Sappey is the only one to give it a cephalic ending ; he represents it with the pike and carp as curving outward at the first cervical vertebra and emptying directly into the jugular. In Scorpcenichthys the myelonal trunk bifurcates directly behind the skull ; each fork passing outward between the skull and atlas unites with the lateral lymphatic trunk in forming the cranial lymphatic trunk, and as stated above the occipital sinus marks the point of union. 3. The cranial lymphatic trunk follows along the ventro- lateral wall of the skull above the jugular, and shortly before the prootic process is reached dilates into sinus (s), which opens laterally into the cephalic sinus and anteriorly into the abdomi- nal sinus. 4. Trois' description of the dorsal lymphatic trunk in Lophius and Uranoscopus will answer equally well for Scor^pcEiiichthys. In the fin region it splits up into 3 parallel vessels, 2 of which run along at the side and base of the rays and the third is a median trunk that traverses the basal canal of the rays ; the latter trunk receives branches from the fin membrane, there 80 ALLEN being 2 for each spine or ray, and sends outward numerous cross-branches to the lateral trunks ; the two lateral dorsal trunks communicate with the lateral lymphatic trunk through the intermuscular or transverse vessels, and with the myelonal trunk through the neural or interspinal vessels. The first neural vessel passes between the skull and the first neural spine and empties into the cranial lymphatic trunk. 5. With Scorficenichlhys the ventral lymphatic trunk in front of the anal fin is not a paired vessel as described by Trois. Between the ventrals it expands into a large heart-shaped sinus into which the ventral fin sinuses are discharged. They receive the lymph from the ventral fins and are prolonged be- tween the body myotomes and the ventral fin musculature to end in the ventral lymphatic trunk. Two other branches have their origin from between the superficial and profundus ab- ductor muscles of the ventral fin. In the median line the ven- tral lymphatic trunk penetrates between the superficial and pro- fundus abductor muscles, and following along the lower side of the pelvics terminates in the posterior end of the ventral pericardial sinus. The ventral intermuscular or transverse' vessels connect this trunk with the lateral lymphatic trunk. 6. A profundus ventral lymphatic trunk was observed run- ning along the inner surface of the body musculature parallel with the main ventral lymphatic trunk. Connecting branches were noticed between the two in the region of the ventral fins, and it was also in communication with the abdominal sinus through the intercostal vessels ; while anteriorly it emptied into one of the pericardial sinuses. 7. A large pectoral sinus is placed at the base of each pec- toral ; dorsad it unites the lateral trunk and the abdominal sinus, and ventrad it is prolonged to communicate with the ventral pericardial sinus. Into the pectoral sinus is discharged a com- mon trunk formed from the union of the external and internal pectoral sinuses. These sinuses run along at the base of the fin and receive connecting branches from the median pectoral sinus, which traverses the basal canal of the rays and collects the lymph from the fin. Trois is the only one to describe the pec- toral lymphatics, and he represents the n>ain trunks in Loph/us DISTRIBUTION OF LYMPHATICS IN SCORP/ENICHTHYS 8l and Uranoscopus as emptying directly into the cephalic sinus. 8. In Scor-p2 r,. [■m.fl Gh.K . Ma.n Gk.M. P.S S.K/iid.M. S.P.AddM. /l.By.A./V. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 91-106 pls. iv-v July 10, 1906 EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT.1 By James Williams Gidley, Department of Geology, U. S. National Museum. In connection with the work of cataloguing the portion of the Marsh collection of Mesozoic mammals, obtained under the au- spices of the U. S. Geological Survey and now deposited in the United States National Museum, I have made some discoveries of seeming importance in the form of evidence bearing on the question of tooth-cusp homologies in the mammalian molars. This evidence I wish briefly to present in the following pages, hoping it may throw some added light on the very important subject of tooth morphology. Before proceeding, I wish to express my indebtedness to Dr. George P. Merrill for making possible the arrangements for this detailed study of material and for his encouragement in the work ; to Prof. Charles Schuchert, of Yale University, for submitting to my hand the type material of the Marsh collection at New Haven ; and to Prof. Henry F. Osborn of the American Museum of Natural History, for his courtesy in placing the collection of Mesozoic mammals in that institution at my disposal. My thanks are also due Mr. G. S. Miller, Jr., for his valuable aid in selecting study material from the collection of modern mammals in the National Museum and for a clear translation of Herluf Winge's paper on tooth-cusp development. 1 Based on a study of the Mesozoic Mammal Collection in the U. S. National Museum. Proc. Wash. Acad. Sci., July, 1906. 91 92 GIDLEY Of the several theories thus far advanced for the evolution of the teeth, none has been entirely satisfactory, and there is still a wide disagreement among authorities, especially as regards the position of the primary cone or " protocone " in the upper molars. As proposed by the late Prof. E. D. Cope and sup- ported by Prof. Henry F. Osborn, the primary cone is to be found invariably on the inner or lingual side of the trigonodont upper teeth, and is the homologue of the central cone in Tri- conodon, in which the three main cusps are arranged in an antero-posterior line, the trigonodont molar having been derived from this form through the shifting of the two lateral cones to the outside. The central cone {protocone) remaining on the inner side, thus forms a triangle {trigori) with the apex pointing inward. In the meantime, according to this theory, the cusps of the lower molars are supposed to have moved in the opposite direction, leaving the central cusps (flrotocoui'd) on the outside, forming an oppositely directed triangle (trigonid). Thus the primary cones of the upper and lower molars in shifting have completely reversed their positions in relation to each other, the primary cone of the upper molars not only moving to the inner side of the crown, but taking a position in the series inside the primary cone of the lower molars as well. This theory, so skillfully worked out by Osborn, has been widely accepted as satisfactorily explaining the problem of tooth- cusp evolution. But recent paleontological and embryological investigations have thrown a large amount of discredit on the whole theory. As stated by Wortman, Scott has shown most conclusively, from paleontological evidence, that in the upper molariform premolars the primary cone is on the outer side and the subsequently added cusps have a very different history from that proposed by the tritubercular theory for the true molars. The embryological researches of Woodward, Tacker, and others have not only confirmed Scott's theory for the premolars, but show also that in all groups of mammals investigated the antero- external cusp or paracone is first to appear in the permanent upper molars and milk molars, as it does in the premolars, and the order of appearance of the other principal cusps is practi- cally the same as proposed by Scott for the premolars. EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT 93 Woodward1 found that in Ccntctcs and Ericulus the main in- ternal cusp, usually termed the protocone, was first to develop, but he believed this cusp to be the paracone, the whole tooth representing only the antero-external triangle of such a form as Talpa, the protocone and metacone not having been de- veloped. This, as stated by Woodward, is a modification of Mivart's view published in 1868, 2 in which he states his belief that in Ccntctcs, Chrysocloris* and like forms, the main portion of the crown represents the union of the two external prisms of Talpa and like forms. According to Mivart, the main internal cusp of Ccntctcs, Ericulus, Chrysocloris, etc., was derived by the fusion of the paracone and metacone, while the protocone and hypocone are wanting or rapidly diminishing in size and importance. According to both Woodward and Mivart, therefore, in these forms, which have been considered typical trituberculates, the outer cusps are developments of the cingulum, while the main internal cusp has been wrongly termed the protocone and is in reality the paracone, according to Woodward, or combined paracone and metacone, according to Mivart, while the inner cusp (protocone) is greatly diminished in size or has entirely disappeared. These two authorities, there- fore, are agreed on the two points of principal importance regard- ing Ccntctcs and Ericulus, viz : (1) the location of the paracone in the main internal cusp and (2) the ultimate loss of the protocone. I strongly concur in these views, for in a series of upper molars, including Potamogalc, Solcnodon, Ccntctcs, Ericulus, Hcmi- ccntctcs and Chrysocloris (see figs. 1-6, pi. IV), the stages sug- gesting the gradual diminishing and final disappearance of the protocone are very complete, amounting almost to demonstration, and there can be little doubt that the molars of the Ccntctcs and Chrysocloris type have been derived from forms similar to that of Potamogalc, involving the loss of the protocone. In conse- quence of this the paracone, or combined paracone and meta- cone, comes to be the principal inner cusp. In Potamogalc the 1 Proc. Zool. Soc. London 1S96, 588-589. 2Journ. Anatomy and Physiol., Vol. II, 139, 1S6S. 3 The form figured by Mivart has since been removed to a distinct genus, Bematiscus Cope, Am. Nat., XXVI, 1S92, 127. The typical Chrysocloris upper molar has no trace of a protocone. 94 GIDLEY protocone is quite prominent and still typical in form, while in Solenodon it is much reduced and is beginning to divide trans- versely, or more probably is beginning to separate from a like- wise reducing hypocone. This is in favor of the view held by Mivart that the simple inner cusp in Potamogale and like forms is in reality the fused protocone and hypocone. The reduction is carried still further in Centetes, in which two inner cingulum-like cusps appear, one on each side of the enlarged paracone. In Chrysocloris and Hemicentetes the inner cusp (protocone and hypocone) has entirely disappeared. Regarding Mivart's " fusion theory," I am inclined to believe that Woodward has not given due weight to the evidence cited by Mivart and that there is considerable support for this theory to be found in the modern bats and insectivores. Mivart con- sidered the Potamogale molar as an intermediate form between molars of the Talfa type, having twro external triangular prisms, and those of Centetes and Ericulus, having only one such prism. He pointed out that in Potamogale there is " a very interesting approximation of the triangular prisms," in which the paracone and metacone, although still remaining distinct, are in very close juxtaposition. This view is strongly supported by a series of bat molars to which Mr. G. S. Miller has kindly called my attention. In this series, which includes Vesfie?-tilio, Scotophilia and Harpiocefhahis^ are suggested the successive steps from Talfa to Potamogale in the insectivore group. Vesfertilio represents the normal or more generalized form, in which the protocone is large, the paracone and metacone are widely separated, and the external styles are nearly equal in size. The mesostyle is much reduced in Scoto-philus and is drawn inward, the paracone and metacone are more closely appressed and the protocone is somewhat shortened. In Har- piocephalus l the mesostyle has disappeared, the parastyle and 1 The skull of Harpiocephalns from which this description was taken was obtained by Mr. G. S. Miller through the kindness of Oldfield Thomas, of the British Museum. Unforunately it came too late to be photographed and figured uniformly with the series. Its place is taken on Plate III, by an outline drawing from a figure for Wilhelm Peters' Fledermause des Berlines Museums fiir Naturkunde (a projected monograph of the bats). EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT 95 metastyle have drawn closer together and compose the entire outer portion of the crown, while the paracone and metacone are closely approximated, forming the greater part of the inner portion of the crown, the protocone being very much reduced. Thus in Harfioccphalus a stage is reached nearly analogous to that of Potamogale^ the principal difference being that the metacone is the dominant cusp instead of the paracone, as in the latter genus.1 From these comparisons it seems reasonably clear that such forms as Centctes, Ericulus and Chrysochloris have attained a secondary or pseudo-tritubercular form by passing through some such stages of evolution as are suggested by the two series here selected. Other examples of a fusing paracone and metacone and reducing protocone may be found in the molars of some of the creodonts and carnivorous marsupials and in the sectorials of many of the carnivores. From the foregoing it now seems to be demonstrated beyond question that the main inner cone of Centetes and Ericulus is not the protocone as observed in normal groups, but, if not entirely made up of the primary cusp (paracone), it at least in- volves that element and Woodward's contention that the evi- dence of embryology is in entire harmony for the molars and premolars is not controverted by these seeming exceptions as supposed by Osborn. Wortman of late has strongly opposed what he terms the "cusp migration theory," and has brought considerable evi- dence to showr that, in the creodonts and carnivores, at least, the cusps of the upper molars in general are homologous to those of the molariform premolars and have had substantially the same history in their development. Against this combined evidence Osborn 2 has recently re- affirmed the tritubercular theory, " as originally proposed," resting the whole question on the point of evidence as to " whether the main reptilian cone, or protocone, of the ances- 1 In the Laramie mammals I find that the metacone equals or is larger than the paracone in those forms in which the postero-external heel is well developed in the upper molars. 2 Amer. Journ. Science (4), Vol. 17, 1904, 321-323. 96 GIDLEY tors of the mammals was found upon the antero-internal side or on the antero-external side of the upper molars." This evidence, according to Osborn, is in favor of the tritubercular hypothesis, and conclusive evidence of the theory is furnished in the Jurassic mammal molars. However, a study of all the mesozoic mam- mal material available has led the present writer to exactly opposite conclusions. Unfortunately, Osborn's observations were confined to a very limited amount of material, and from a careful examination of the teeth of Triconodon and Dryolestcs,1 two forms especially studied by him, it seems that his conclusions were based on evident, though perfectly excusable, errors of observation, due doubtless to the minuteness of the teeth and their dark color, which make it difficult in many cases to distinguish, between a fracture and the natural surface of the tooth. Thus, according to Osborn,2 the upper molars of Dryolestes are " broadly trans- verse or triangular and upon the internal side of each is a large, conical, pointed cusp,/r, supported by a large stout fang, . . . The external portion of the crown is depressed, and bears one large antero-external cusp ? pa and one smaller postero-external cusp ? me which is either partially worn away or less pronounced in development." But there are two important cusps not noted by Osborn, one an external cusp placed anterior to the main external cusp, the other a small but well-defined intermediate cusp appear- ing on the posterior transverse ridge. Thus there are five distinct cusps instead of three, as stated by Osborn, and these do not form a trigon in the sense that this term has been used, for the main external cusp is in the middle of the base of the triangle instead of forming one of its angles. In the upper molars of Triconodon the three principal cusps are arranged in a direct line, and are nearly equal in size and form, and the two lateral cones are each supplemented by a small but well-defined internal basal heel-like cusp and an external basal cingulum. The main cusps are flattened externally into a con- tinuous wall in one species (see PL V, fig. i), while they are 1 The specimens studied by the present writer and referred to these genera are from the Atlantasaurus beds of Wyoming. These beds are usually referred to the upper Jurassic, although they may be lower Cretaceous. 2Amer. Journ. Science (4), Vol. 17, 1904, 322. EVIDENCE BEARING ON TOOTH-CUS1' DEVELOPMENT 97 much rounded and deeply divided on the inner or lingual side. Thus, there is not the slightest suggestion of a tendency toward an outward movement of the lateral pair of cusps, while it is easily conceivable that the continued development of the two inner heel cusps and outer cingula wrould early result in a gen- eral form of tooth very different in pattern from the tritubercular type which might form the basis for such molars as those of the diprotodont marsupials and many of the rodents or even of the manatee and mastodon. I do not wish to be understood here as implying any relationship between these very diverse forms, but as especially emphasizing the fact that in Triconodon is sug- gested an easy and not improbable way in which some complex molars may have been derived without having passed through the typical tritubercular stage. Thus, it is shown by this restudy of the two forms, which according to Osborn represent successive stages in the evolution of the mammalian molar, that the gap between them, which was already great, even according to Osborn's interpretation, is very greatly increased especially from the tritubercular theory standpoint. Moreover there is no evidence, in the way of in- termediate forms, indicating that Dryolestes ever passed through a stage strictly analogous to that of Triconodon or that the main internal cusp is in any way homologous to the central cone in the Triconodon molars. Furthermore, a critical com- parison of these two forms shows that such an hypothesis is beset by many difficulties. The following are the principal ones : (1) The molars of Triconodon are larger and fewer in number than in Dryolestes indicating a generally higher specialization. (2) The lateral cones in Triconodon are already comparatively much specialized, being suplemented by growths of the cingu- lum externally and heel cusps internally and thus do not es- pecially resemble, either in form or proportions, any two of the external cusps in Dryolestes. (3) The external portion of the upper molar in Dryolestes (see PI. V, figs. 2 and 3) is composed of three simple connate cusps supported by two fangs, their general appearance suggesting an arrangement homologous to the three cusps and two fangs of Triconodon; while (4) the internal portion of the tooth is a high antero-posteriorly com- 98 GIDLEY pressed V-shaped cusp supported by a single fang, centrally placed, and exposed on its inner side for the greater part of its length, the maxillary bone apparently not yet having formed a completed socket, or alveolus, for its reception. Thus the whole construction of the inner cusp, which is highly sugges- tive of a heel development, differs materially from the central cone of Triconodon. A O O O B °-=0— ° °^y=° °=o=° c 0=0=0 0=0-0 D VAVAV E F J Fig. 11. Phyletic History of the Cusps of the Ungulate Molars. A, Reptilian Stage, Haplodont, Permian. B, Protodont Stage {Dromotherium) , Triassic. C, Triconodont Stage {Amphilestes). D, Tritubercular Stage (Spalacothe- rium). E, Tritubercular-tuberculo Sectorial, Lower Jurassic. F, The same, in Upper Jurassic. G, The same, in Upper Cretaceous. H, The same, Puerco, Lower Eocene. /, Sexitubercular-sexitubercular, Puerco. J, Sexitubercular- quadritubercular, Wahsatch. (After Osborn.) Considering the outer portion of the Diyolestes molar as homologous to the three cones and two fangs of Triconodon, EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT 99 ^ ' o"o a * 000 £ 3 X^Q^ -Bc^^^ £ 4 $&# QOOCfcQ© a 5 Fig. 12. Suggested Phyletic History of T-vo Types of Complex Molars. [As in Osborn's diagram, the solid black dots represent the cusps of the upper molars, the circles, those of the lower molars.] 1 to 6, Phyletic history of the " Tritubercular " type; a to d, Phyletic history of the " Triconodont " type; e,f, From the brachyodont Triconodont stage to the bilobed hypsodont type of molar. A, B, C, E and G compare with A, B, C, E and G in Osborn's diagram, fig. 11 ; ^, Dryolestes type, Atlantosaurus beds (? Upper Jurassic); 5 and 6, Proto- lambda or Pediomys type, Laramie beds (Upper Cretaceous); d, Triconodon type, Atlantosaurus beds ( ? Upper Jurassic) ; f Palceolagus type, White River beds (Oligocene). IOO GIDLEY the derivation of this type of tooth is much simplified, it being not so far removed from the primitive reptilian condition, and though diverging on different lines, is no more specialized, as a whole, than the Triconodon type of tooth, the differentiation being carried on more rapidly in the latter in the special de- velopment of the anterior and posterior lateral cones and their accessory cusps, while in Dryolestes the specialization has apparently been centralized in the development of the high, narrow, heel-like cusp and its supporting fang on the inner side of the molar. This view is strongly supported by the evidence obtained from still another characteristic Atlantosaurus-beds type of molar represented by Dicrocynodon. In this form, PL V, fig. 4, the same primitive arrangement of three cusps and two fangs is preserved in the outer portion of the tooth, while on the internal side a large secondary cusp has been developed differing widely in character from that of Dryolestes. This cusp is a laterally compressed cone supported by two rudimentary fangs and is joined to the outer portion of the tooth by a high, wedge-shaped ridge. The base of the inner cone is greatly expanded antero- posteriorly, curving gently outward toward the external portion of the tooth. Thus the crown, as a whole, is greatly constricted medially with the inner and outer portions superficially resem- bling each other. From these observations two important conclusions may be drawn : First, that, leaving out of consideration the multitu- berculates, there are among the mammals of the Atlantosaurus beds at least three distinct forms of upper molars representing three primitive types of about equal specialization apparently leading off in entirely independent lines. Probably only one of these, Dryolestes, represents an ancestral type from which the Upper Cretaceous and later forms possessing trigonodont molars may have been derived. Second, that the evidence derived from the Atlantosaurus beds mammals entirely supports the evidence of embryology and agrees in general with the "pre- molar analogy " theory. Thus, the evidence from all sources points overwhelmingly to the conclusion that the primary cone is to be found on the outer side in the upper molars of primi- EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT IOI tive trituberculate forms and in all forms derived from a tritu- bercular type of tooth as well, except where the main inner cone (protocone) has been reduced secondarily. The opposite view held by the tritubercular theory now apparently stands on very insufficient evidence, and the proposition that the protocone, of Osborn, represents the primary cusp is entirely without support. The lower molars of the Atlantosaurus beds mammals fur- nish abundant additional evidence along the line of conclusions regarding the shifting of three cusps from a straight line to form the primitive triangle. In such forms as Dryolcstes and Paurodon we have trituberculate molars in the primitive or forming stage, and, what is most significant, the cusps resemble very closely, both in position and relative proportions, those of the premolars of later types in their early stages of transition to the molariform pattern. In the lower molars of Paurodon the crown consists of a high, pointed cusp (protoconid), centrally placed, a low posterior heel, a small anlero-internal cusp (para- conid), and a very small median internal cusp (metaconid). The last two form the base of the trigonid. In Dryolcstes both the trigonid and the pimitive heel are somewhat more advanced in development. In still other forms, such as Manacodon and Tinodon, the two internal cusps are relatively large and the trigonid is fullv developed, while the heel, or talonid, is very small or entirely wanting. In all the paraconid and metaconid are entirely on the internal side of the crown, and in these and all the material examined there is not the slightest evidence of any shifting of the cusps, but they seem to have arisen in the positions they now occupy.1 In Paurodon the heel is apparently as much or more developed than either of the internal cusps and seems to have made its appearance even in advance of the metaconid. Also the metaconid is still very rudimentary and is just budding off near the base of the protoconid, but little pos- terior to its apex and midway of the entire length of the crown, while the place of origin assigned to it by the tritubercular hypothesis is already occupied by the comparatively large heel. 'This is in accord svith the general conclusions on tooth cusp development reached bv Herluf Winge as early as 1882. Widinsk Meddelelsor fn den natur- hist. Florening e Kjobenhavn. iSS;. p. iS. 102 GIDLEY From these observations it seems apparent that the trigonid of the lower molars is not the reverse of the trigon of the upper molars, as held by advocates of the tritubercular theory, and the homologues of the elements of the upper and lower molars, as proposed by this theory, are far from being apparent. (This also accords with the conclusions of Winge.) The lower molars of Triconodon differ from any of the forms just described. They are composed of three nearly equal cone-like cusps arranged like those in the upper molars of this genus in an antero-posterior line. There is no cusp corres- ponding with the metaconid in Dryolestes. There is a continu- ous basal cingulum on the inner face of the crown, and the posterior cusp is in no way homologous, except in position, to the heel in the lower molars of Paurodon and Dryolestes. The mammals from the upper Cretaceous Laramie beds show a great advance in development. The molars of the tritubercu- late forms of this horizon have passed into a second well-defined stage of specialization which, though varying greatly in detail in the various types, conforms in general to a distinctive pattern which may readily have been derived from some Atlantosaurus- beds form, such as Dryolestes. An upper molar of Pediomys Marsh, a typical example of the Laramie tritubercular molar, compared with the corresponding tooth of Dryolestes, presents the following differences and indicates the principal lines of progression : (i) The main internal cusp (prolocone) is much broadened antero-posteriorly ; (2) a second small V-shaped intermediate cusp (protoconule) has been added ; (3) the postero-external cusp (metacone) has greatly increased, nearly equaling, both in size and importance, the median external, or primary, cone (paracone), while the antero-external cusp ( parastyle) has re- mained small and undeveloped. A correspondingly pro- gressive development marks the trigonid and heel of the lower molars. Thus, the " trigonodont " tooth, or a type of molar with three principal cusps of almost equal importance, arranged in the form of a triangle, makes its first appearance in the Laramie. This pattern of tooth Cope early recognized as a general primi- EVIDENCE BEARING ON TOOTII-CUSP DEVELOPMENT IO3 tive type, and on its representatives in the lower Eocene he founded the tritubercular theory. That this type is primitive and many, at least, of the later forms have been derived from it, have been too conclusively demonstrated by Cope, Osborn, Scott and others to be seriously questioned ; but this early trigonodont form, as is now evident, was derived in a totally different way from that assumed by the tritubercular hy- pothesis. An especially interesting feature in these Laramie forms is the oft-repeated appearance in the upper molars of a back- wardly extended outer heel-like cusp connected by an elevated ridge with the postero-external cusp. This portion of the tooth is thus converted into a more or less perfect sectorial, or cutting, blade, against which the anterior blade of the trigonid shears, while the greatly broadened heel or talonid of the lower molar, extending backward under the antero-posteriorly expanded protocone of the upper molar, forms a successful crushing apparatus. Thus, so early as the Cretaceous the prevailing molar types were about equally equipped for use as cutting or crushing mechanisms. The creodonts and carnivorous marsu- pials seem to have early taken advantage of the sectorial blade to the neglect of the crushing heel which gradully diminished in relative size and importance, while in many other forms, using the crushing portion of the tooth most, the sectorial blade was early lost. Another special character marking the advance of the upper Cretaceous mammal molars is the first indication in a few forms of the postero-internal cusp [hypocone), which forms the fourth main cusp in the later quadra-tubercular type of molars. This cusp has apparently been derived, according to the evidence of these Laramie types, from independent sources in different groups of mammals. In a form which Marsh has referred to Tclacodon a strong cone-shaped cusp has developed on the postero-internal cingulum of the tooth indicating the deriva- tion of the hypocone from that source. Another form, appar- ently representing an undescribed genus (PI. V, fig. 7) is evidently developing a hypocone from the primitive posterior intermediate cusp. Still another form, represented by Proto- 104 GIDLEY lambda Osborn, seems to indicate a third source from which the hypocone may have developed. In Protolambda the internal heel (protocone) is broadly expanded and flattened posteriori}'' without a cingulum, yet the peculiar shelf-like form of this por- tion of the tooth suggests the origin of a hypocone budding off from the protocone independently of either the cingulum or pos- terior intermediate cusp. From such a form as that presented in PL V, fig. 7, it is but a short step to the typical selenodont artiodactyl type of molar through the progressive development of the V-shaped posterior intermediate cusp. The addition of a second posterior cusp budding off from the enlarged postero-intermediate cusp would readily convert the tooth into a perissodactyl type of molar. Thus is suggested a fourth possible source of origin for the hypocone. This does not necessarily imply an actual relation- ship of this particular form to the ungulates, but indicates a type closely resembling them which differs widely from the primitive carnivores and insectivores, in which the hypocone, when present, was undoubtedly derived from the cingulum. These observations suggest especially that apparently homol- ogous elements in the teeth of the more highly complex forms may often arise from different sources. The correlation and homologies of the cusps of the lower molars in comparison with those of the upper series have, for the most part, been left out of this discussion. One observa- tion, in this connection, however, of seeming great importance and significance should be noted here. In examining a large number of examples of both living and extinct forms, I have found the following associations between the heel of the lower molars and the protocone of the upper teeth to hold constantly true, viz : A functional, broad, crush- ing protocone is invariably associated with a well-developed crushing heel in the opposing lower molar. A reduced or vesti- gial protocone is invariably associated with a correspondingly reduced or vestigial heel in the opposing lower molar. Since the heel of the lower molars is admittedly of secondary origin, this feature alone would seem to argue stroncrlv for a like sec- ondary origin for the protocone in the upper molars. EVIDENCE BEARING ON TOOTH-CUSP DEVELOPMENT IO5 SUMMARY AND CONCLUSIONS. Summing up the evidence derived from this preliminary study, the following conclusions are suggested : 1. That the evidence obtained from the Mesozoic mammal teeth furnishes no support to the tritubercular theory in so far as it involves the position of the protocone and the derivation of the trigonodont tooth from the triconodont stage through the shifting of the lateral cones outward in the upper molars and inward in the lower molars. 2. That it supports entirely the embryological evidence that the primary cone is the main antero-external cusp, or paracolic, having retained its position on the outside in most upper molars (see exceptions above, p. 95). 3. That it agrees in the main with Huxley's " premolar- analogy " theory, as supported by Scott. 4. That the molars of the Multituberculates, Triconodoti, Dryolestes and Dicrocynodon, were apparently derived inde- pendently from the simple reptilian cone ; hence the supposi- tion follows that the trituberculate type represents but one of several ways in which the complex molars of different groups may have been derived.1 5. That in the forms derived from the trituberculate type of molar the order of succession of the cusps is not the same in all groups, and apparently homologous elements are sometimes de- veloped from different sources. Hence it follows that no theory involving an absolute uniformity of succession in the development of complex molars zu ill hold true for all groups of mammals. In the foregoing pages I have restricted the use of Osborn's tooth-cusp nomenclature for the reason that, in this particular discussion, there are some cases in which it is not strictly appli- cable and might lead to confusion. On similar grounds Dr. Wortman2 has expressed the opinion that all attempts to establish a tooth-cusp nomenclature founded on supposed homologies are "foredoomed to failure" and should be entirely abandoned as " useless and confusing." I 1 Somewhat similar conclusions have been reached from different reasoning by E. S. Goodrich, M. Tims and others. 2Amer. Journ. Science (4), Vol. 16, 1903, 265-368. Proc. Wash. Acad. Sci., August, 1906. 106 GIDLEY agree with the general sentiment expressed {of. ctt., p. 366) that, owing to the adoption of different plans in different groups of mammals for increasing the complexity of their molars, no terminology founded on the basis of cusp homologies can be made strictly applicable to all the mammalia. I do not, how- ever, consider this sufficient ground for abandoning absolutely so convenient a system of nomenclature as that proposed by Osborn. Granting that many of the terms proposed are founded on mistaken homologies, it does not necessarily follow that they need be in the least confusing, as suggested by Wortman. For in any system used, in order to make that system of greatest convenience and highest utility, the names once adopted should be permanent and not subject to transfer or substitution on any ground of changed conceptions of homologies or history, for the same reason that generic and specific names are retained regardless of the fact that they may have been given to denote some supposed affinity or characteristic which may later have proved entirely erroneous. Viewed from the nomenclature standpoint, therefore, the convenient names proposed by Osborn have come to assume an individuality which conveys a far more definite meaning than any purely descriptive terms, be they of relative position or supposed homologies. Moreover, they have the valuable ad- vantages of clearness and brevity in description. On these grounds, in the opinion of the present writer, and for the added reason that great confusion would inevitably result from any change in a terminology that has found its way into so many publications, Osborn's nomenclature should be retained as orig- inally proposed. Thus the term "protocone" always means the main antero-internal cusp of a normal upper molariform tooth, whether that element is regarded as the original primary cusp or otherwise. The objection that the terms are not universally applicable is scarcely worthy of consideration since they are widely appli- cable to the great majority of mammalian molar types, without in the least interfering with the use of terms descriptive of " rel- ative position only," which may be used in any cases where Os- born's terms do not apply. EXPLANATION OF PLATE IV. (All figures except fig. 9, three times natural size.) Fig. 1. Potamogale — left upper jaw (No. 124327 U. S. N. M.) ; habitat, Africa. Fig. 2. Solcnodon — left upper jaw (No. 2230, U. S. N. M.) ; habitat, Cuba. Fig. 3. Centeles — left upper jaw (No. 63316 U. S. N. M.) ; habitat, Mada- gascar. Fig. 4. Ericulus — left upper jaw (No. 1224S8 U. S. N. M.) ; habitat, Mada- gascar. Fig. 5. Hemicentetcs — left upper jaw (No. 63319 U. S. N. M. ) ; habitat, Africa. Fig. 6. Chrysochloris — left upper jaw (No. 616S6 U. S. N. M.) ; habitat, Africa. Fig. 7. Vespertilio fuscus — left upper jaw (No. 62736 U. S. N. M.) ; habitat, Washington, D. C. Fig. 8. Scotofhilus huhli — left upper jaw (No. 1 13463 U. S. N. M.) ; habitat, Philippines. Fig. 9. Harpiocepfialus — right upper jaw. (Outline drawing taken from a plate prepared in 1880 by Wilhelm Peters for a monograph of the bats. This monograph was never published.) Proc. Wash. Acad. Sci., Vol. VIII. Plate IV. CHEEK TEETH OF LIVING INSECTIVORES AND BATS EXPLANATION OF PLATE V. Figs, i and la. Triconodon ? bisulcus Marsh (Atlantosaurus beds), left upper molars, m2 and m3, crown and external views. Six times natural size (No. 269SU. S. N. M.). Figs. 2, 2a and 2b. Dryolestes sp. (Atlantosaurus beds), left upper molars; crown, external, and posterior views. Seven times natural size (No. 2845 U. S. N. M.). Fig. 3. Dryolestes, first right upper molar, m1 ; crown view. Eight times natural size (No. 2S39 U. S. N. M.). Figs. 4 and 4a. Dicrocynodon sp. (Atlantosaurus beds), left upper molars; crown and external views. Six times natural size (No. 2715 U. S. N. M.). Figs. 5, 5a, 5^ and 5c. Paurodon sp. (Atlantosaurus beds), right lower molar, m2, crown, external, internal and posterior views. Eight times natural size (No. 2733 U. S. N. M.). Figs. 6, 6a, 6b and 6c. ? Pediotnys sp. (Laramie beds), left upper molar; crown, external, posterior, and anterior views. Eight times natural size (No. 5062 U. S. N. M.). Figs. 7, "ja and "jb. Gen. et sp. indt. (Laramie beds), left upper molar; crown, external and anterior views. Eight times natural size (No. 5076 U. S. N. M.). Proc. Wash. Acad. Sci., Vol. VIM. Plate V. TEETH OF MESOZOIC MAMMALS PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. m-139. August 14, 1906. NEW STARFISHES FROM THE PACIFIC COAST OF NORTH AMERICA. By Walter K. Fisher, Leland Stanford Junior University. The United States National Museum recently sent the writer most of the starfishes in its collections from the west coast of North America. These collections comprise material dredged by the Fisheries Steamer Albatross, as well as specimens from other sources. As it will be some time before the final report can be completed and published, the following species are described in advance: Lepty chaster pacijicus. Lepty chaster anomalus. Astropecten ornatissimus. Ltiidia ludwigi. Luidia asthenosoma. Henricia aspera. Hcnricia polyacantha. Crossaster alternatus. Crossaster boreal is. Rathbunaster calij vrntcus, new genus and species. In the Bulletin of the Bureau of Fisheries for 1904, Vol. XXIV, June 10, 1905, pp. 291 to 320, the writer published 1 new genus, 2 new subgenera, and 24 new species, based on material collected by the Albatross in Alaska in 1903, and off Proc. Wash. Acad. Sci., August, 1906. v'111) 112 FISHER California in 1904. Most of these forms are found also in the National Museum material, collected at an earlier date. The new forms described below will be figured in the final report. Family ASTROPECTINID^) Gray. Genus Leptychaster l Smith. Lepty chaster Smith, Ann. and Mag. Nat. Hist., Ser. 4, xvii, 1876, no. Leptopty chaster Smith, Philos. Trans., Zool. Kerguelen Island, clxviii, 1879, 27^- LEPTYCHASTER PACIFICUS Fisher, new species. Ravs 5. R = 43 mm. ; r = 14 mm. ; R= $r. Breadth of ray at base 16 mm. General form similar to that of L. arctfeus (Sars) but disk rather broader. General form flattened ; rays evenly tapered, bluntly pointed ; interbrachial angle slightly rounded, but abrupt ; abactinal surface subplane ; margin of rays defined by inferomarginal plates, rounded ; superomarginal plates well- developed, relatively larger than in L. arcticus, forming a fairly conspicuous margin to abactinal paxillar area ; actinal surface slightly convex ; actinal interradial areas slightly smaller, and intermediate plates fewer than in L. arcticus. Tube-feet pointed, the proximal with a rudimentary subcorneal disk; superambulacral plates small. Abactinal paxillar area fairly compact, the paxillee decreas- ing in size toward center of disk, midradial line, and end of ray ; smallest paxillar in center of disk, the largest on margin of area at base of ray. Paxillas similar in character to those of L. arcticus, but slightly larger, and spinelets a trifle longer. Base of pedicel flaring into a roundish plate with 4 or 5 short rather irregular lobes by which the plates touch or imbricate slightly, and between which the papulse emerge. Larger paxillar with about 25 peripheral and 30 central slender delicate 1 This is the original spelling, and, as it is very evident that there is no typo- graphical error, this name should be employed instead of Leftoftychaster. NEW STARFISHES FROM THE PACIFIC COAST II3 terete blunt spinelets ; spinelets occupying center of tabulum form a coordinate flat-topped group, usually stand upright and are crowded; peripheral spinelets usually radiate and are not equal in length. Marginal plates short, band-like, but both series more con- spicuous than in L. a'rcticus; superomarginal plates, 30 in number from interradial line to extremity of ray much wider than long on proximal half of ray, the width rapidly decreasing on outer portion until plates are nearly quadrate. Plates form an arched bevel to margin of abactinal area, are separated by deep fasciolar grooves, and are covered with short delicate terete spinelets which form a close nap all over exposed surface. Inferomarginals corresponding to superomarginals, beyond which they extend laterally forming margin of ray; separated from superomarginals by rather wide groove ; short, band-like, separated by fasciolar furrows, forming well-arched bevel to actinal surface ; first plate about twice as wide as corresponding superomarginal ; all densely covered with small spinelets similar to those of superomarginals, but a trifle larger, those of trans- verse median region slightly squamiform and directed outward. Actinal intermediate areas rather smaller than in L. arcticus; one series of intermediate plates extending about three-fourths length of ray or to eighteenth inferomarginal ; a second series extending to seventh or eighth plate, and a third series con- fined to angle bounded by adjacent first 2 plates. Intermediate plates with a low tabulum crowned by a coordinate group of 15 or 20 papilliform spinelets, those in center being slightly thicker and more clavate than the peripheral ones. Adambulacral plates about as wide as long with a rounded furrow margin, but first 2 or 3 plates wider than long and with more angular margin. Armature consists of (1) a furrowr series of 4 (more rarely 5) slender, rather long, blunt cylindrical spinules, the two central being slightly the longest or the 4 subequal ; (2) on actinal surface are 2 or 3 longitudinal series of about 4 similar spinules which decrease in size toward outer edge of plate ; third series when present more irregular, its spinelets distinctly tapered, slenderer, shorter and sharper. Furrow spinelets usually bent back from furrow, and arma- ture has a decidedly crowded appearance. ii4 FISHER Mouth-plates narrow, the free margin of each being longer than that adjacent to first adambulacral, and the combined plates forming a salient angle into actinostome. Margin of plate with a series of about 15 slender tapering spinules, de- creasing in length from inner to outer end of plate. About 8 to 10 of these are more regular and occupy the free actinosto- mial margin, the rest being adjacent to first adambulacral plate, between which and the mouth-plate there is a fairly wide suture. A series of numerous similar spinules stands on edge of suture furrow, and sometimes an incomplete, irregular, intermediate series is present. Madreporic body situated about its own diameter from inner edge of superomarginal plates, fairly large, surrounded and par- tially obscured by large paxillae ; striations deep, coarse, irreg- ular, centrifugal. Type, No. 21925, U. S. Nat. Mus. Type locality, Alba- tross Station 2862, near north end of Vancouver Island (inside) in 238 fathoms, on gray sand and pebbles. This well-marked form has larger superomarginals than any previously described species. I have compared the type with a specimen of L. arcticus (No. 17992, U. S. Nat. Mus., " Sta. 21, Cashes Ledge'') having a major radius of 35 mm. In L. arcticus the proximal superomarginal plates are not conspicu- ously larger than those of outer third of ray. They are roundish and resemble large paxillae, but in L. pacijicus the proximal plates are much wider than those of distal half of ray, and the plates decrease regularly in width all along ray. The mar- ginal plates of L. arcticus are shorter, hence more band-like, than in L. pacificus, there being 36 plates to R = 35 mm., while in L. pacijicus, with R 43 mm., there are but 28 to 30 plates. On account of the difference in size of the superomar- ginals in the 2 species, the abactinal paxillar area is narrower in L. pacijicus. The actinal interradial areas of L. arcticus are slightly larger than in L. facijicus and the paxillae are more crowded. The present species seems to bring Leptychaster nearer to both Bathybiastcr and Psilastcr, on account of the larger superomarginal plates. There are, of course, no special spines on the marginal plates of any Leptychaster. NEW STARFISHES FROM THE PACIFIC COAST II5 LEPTYCHASTER ANOM ALUS Fisher, new species. Rays 5. R= 27 mm.; r = 17 mm.; 7?=i.6r. Breadth of ray at base, 19 mm. In general form and ornamentation greatly resembling Par- astropccten inermts Ludvvig. Disk broad, rays short, broad and blunt ; interbrachial arcs shallow and wide ; abactinal sur- face subplane, capable of slight inflation ; marginal plates con- spicuous, devoid of enlarged spines or spinelets, but covered with granules and granuliform spinelets; actinal intermediate areas broad ; adambulacral plates with 3 or 4 furrow spines ; small superambulacral plates present ; a very tiny anal pore present. Abactinal paxillar area compact ; paxillas arranged in not very regular oblique transverse rows at sides of ray ; without order in median radial area and center of disk. Paxillar largest at base of ray and in interradial areas decreasing conspicuously in size toward center of disk and tip of ray ; larger at sides of paxillar area than in mid-radial region. Paxillas with subcir- cular bases having 5 or 6 very short irregular lobes, by which neighboring plates touch, or even imbricate in center of disk and mid-radial area. Papulae in 5's and 6's (except in center of disk and along mid-radial lines where they are absent). Column of paxilla about as high as breadth of base, flaring at summit, the largest crowned with a coordinate noriform group of about 40 or 45 short, terete, often clavate, round-tipped spinelets ; of these about one-half form a peripheral series and are a trifle slenderer and longer. On the smaller paxillas the spinelets de- crease markedly in size, but only slightly in number. Supermarginal plates, 15 in number from median interradial line to extremity of ray form an arched bevel to border of abac- tinal surface ; plates shorter than wide, but increase in length on outer half of ray. Plates of both series separated by trans- verse narrow deep fasciolar grooves and a narrow deep groove (not so deep as transverse grooves) separates superomarginal from inferomarginal series. Superomarginal plates covered with short, terete, blunt granuliform spinelets, similar to but larger than paxillar spinelets, becoming well-defined slender Il6 FISHER spinelets in fasciolar grooves. Superomarginal covering is to be considered as a spinelet rather than granules. Inferomarginal plates much wider than long, encroaching more onto actinal area than do superomarginals onto abactinal, and corresponding in position to superomarginals. Spinelets, densely covering surface of plates, larger than those of supero- marginals, and increasing in size toward outer end of plate which projects slightly beyond adjacent end of superomarginal, thus defining the ambitus. Inferomarginal spinelets granuli- form in middle of plate, often attaining a squamiform appear- ance at outer end; spinelets in fasciolar furrows, slender. No enlarged spines of any sort on either marginal series. Termi- nal plate small, granulose, deeply notched below. Actinal interradial areas large ; intermediate plates low-pax- illiform, arranged in chevrons, the series adjacent to adambu- lacrals extending about three-fourths length of ray or to eighth inferomarginal. Plates decrease in size toward margin, are strongly imbricated internally, and the paxillar crowns which are composed of about 25 to 30 clavate obtuse, not very crowded, spinelets (slender when dry) surmount a low convex elevation or tabulum. Well-defined fasciolar channels separate these tabula. Adambulacral plates about as wide as long, with a slightly rounded, angular furrow margin, the angularity being more pronounced in vicinity of mouth plates. Armature consists of (1) a furrow series of 4 (sometimes 3) terete or slightly flat- tened bluntly pointed tapering spinules about as long as plate and graduated in length orad, the longest spine being on aboral end of plate ; or the spinules may be disposed like rays of fan and graduated in length toward either end of series. (2) On actinal surface are about 3 longitudinal series of smaller spine- lets, decreasing in length toward outer edge of plate where the spinelets are like those of actinal intermediate plates. Four spinelets commonly occur in the inner actinal series and about 3-5 in each of the outer; or the 2 latter series may be wanting, the spinelets, instead, forming ah irregular group, especially on outer part of ray where there are frequently upwards to 16 or 20 actinal spinelets. NEW STARFISHES FROM THE PACIFIC COAST 117 Mouth plates narrow, rather prominent actinally, the free margins of the combined plates forming a salient angle into actinostome ; free margin of each plate slightly angular near inner end and longer than the margin adjacent to first adambu- lacral. Armature consists of a furrow series of about 6 or 7 tapering spinules decreasing in length from the inner enlarged tooth, outward, and thence continued along margin adjacent to first adambulacral in about 9 much smaller spinelets similar to those of actinal intermediate plates. A superficial series of similar spinelets follows margin of median suture, increasing in size toward inner angle of plate, and an incomplete more or less irregular series often, but not always, occurs between marginal and superficial series. There is more or less variation in the details of dental armature. Madreporic body rather large, about midway between center and extreme edge of disk. Striations coarse, centrifugal, very irregular; madreporic body sometimes nearly hidden by 5 or 6 large paxillas. Type, No. 21926, U. S. Nat. Mus. Type locality, Alba- tross Station 3310, Bering Sea, in 58 fathoms, on dark sand and mud. Remarks. — This species bears a close resemblance to Paras- tropectcn inermis Ludwig,1 and is probably congeneric with that form, although anomalus has a minute anal pore. The presence of an anal pore is, I believe, a character of scarcely more than specific importance. For instance one species of Astrofccten has been shown by Verrill to possess a minute anus. Although I have not yet had an opportunity to make serial sections of the anal region of anomalus, I have been able to make out a tiny pore in 2 specimens, and the intestine lead- ing to the pore is well developed. It may perhaps seem her- etical to classify the present species with Lefty chaster, but anomalus differs chiefly from L. facificus in having a larger disk, shorter rays, broader actinal interradial areas, and a slightly different ornamentation on paxillre and marginal plates. 'Mem. Mus. Comp. Zool., XXXII, July, 1905, 76, pi. to, fig. 21, 22; pi. xxi, fig. 117; pi. xxii, fig. 126. (Gulf of Panama and Cocos Id., 1,271 and 1,40s meters.) Il8 FISHER The superomarginals are only a trifle, if any, larger in anomalies although the inferomarginals are a little longer and not quite so broad. The chief differences are therefore in proportion. But pacijicus is an undoubted Le-pty chaster, an evident offshoot of arcticus, of the circumpolar fauna. It therefore follows in due course that anomalus is a Leptychaster, although super- ficially different enough from kcrguelencnsis, perhaps, to war- rant another generic designation if we did not have the inter- mediate steps. Without having examined specimens of Parastropecten iner- mis I hesitate to further question the validity of the genus, although frankly I find no generic characters other than the size of the superomarginals that can separate the form from Lefty chaster. At any rate, L. anomalus differs from P. iner- mis in having fewer furrow spines, more paxillae spinelets, 5 and 6 papulae about the very short-lobed roundish plates (instead of 4), and finally in possessing a minute anal pore. The general facies of the 2 forms is strikingly alike. Genus Astropecten Schulze. Astropecten Schulze, Betrachtung der versteinerte Seesterne u. ihre Theile, 1760. There appear to be 3 species of Astropecten off the Cali- fornia coast. One, which I have provisionally identified as A. erinaceus Gray, does not range much north of San Diego, and seems to be a shore form. I have been unable to identify the other two species with any previously described form. I have recently described one of these as Astropecten californicns1 and the other is diagnosed below. In order to contrast the principal characters a synopsis of the 3 forms is added. a. A series of spines along upper edge of superomarginals, and usually, also, a second, parallel longitudinal series, spaced from the above ; size large ; littoral erinaceus. aa. Superomarginals entirely devoid of enlarged tubercles or spines. b. Paxillae larger, about 3 transverse series opposite 2 superomar- ginals at base of ray ; paxillae not irregular and more crowded along radial lines ; the enlarged spine of actinal surface of adambulacral plates, slender, tapering and bluntly pointed. ornatissimus. 'Zool. Anzeiger, Bd. XXX, Nr. 10, June 19, 1906, 299. NEW STARFISHES FROM THE PACIFIC COAST IIO. 66. Paxilla? smaller, about 4 or 5 transverse series opposite 2 supero- marginals at base of ray, crowded and more or less irregular along radial lines; enlarged adambulacra] spine with rounded or truncate tip, and not conspicuously tapered... ca lifo miens. ASTROPECTEN ORNATISSIMUS Fisher, new species. This species differs from its nearest relative, A. californicus, in having shorter rays, larger paxillae with longer spinelets, longer and slenderer adambulacral spines, and longer marginal spines. R — 56 mm. ; r = 14 mm. ; R = ^r. Breadth of ray at base, 16.5 mm. The paxillae afford the most evident difference between orna- tissimus and californicus. In californicus there is a consider- able area around center of disk in which the paxillae are smaller and more crowded than on remainder of disk and on rays, and paxillae of midradial regions are more irregular, at least in arrangement, than along margins of ray. In the present form the large paxillae extend nearly to center of disk, there being only a small area of small paxillae. The paxillae of sides of rays are not in such regular rows and are not easily differentiated from the midradial ones. About 3 or 3^ transverse series of paxillae correspond to 2 superomar- ginal plates at base of ray (usually 5 in californicus), about 5 at middle of ray, and 6 or 7 near tip. Opposite suture between second and third superomarginal plates about 12 or 13 paxillae can be counted across ray to same point on opposite side (18 to 20 in californicus). Large paxillae at base of rays with 15 to 18 peripheral and 10 to 15 central spinelets, which are much longer than in californicus, terete, with rounded or clavate tips. Tabulum of paxilla fairly broad so that both central and per- ipheral spinelets appear spaced, giving the whole an open flori- form appearance. Farther along ray, 1 to 6 central spinelets to a paxilla, and upwards to 15 or 18 peripheral. At very end of ray the paxillae are much smaller. Superomarginal plates 32 to a ray, without enlarged spine- lets or tubercles. General surface covered with short spinelets, delicate except along median transverse line where they are cla- 120 FISHER vate to thimble-shaped, increasing in size toward upper end of plate (same spinelets are markedly squamiform in californicus). Armature of inferomarginal plates very similar to that of cal- ifornicus, there being usually 2 or 3 marginal spines obliquely placed, and, in a line, 3 more spaced, smaller, spines along aboral edge of plate. The auxiliary lateral spines situated just adorad to the regular lateral spines on each plate are longer than the same spines of californicus. Adambulacral furrow spines 3 or 4, similar to those of cal- ifornicus. First actinal series with 2 spines, the aboral being much the longer, tapering, slightly flattened, bluntly pointed, longer and slenderer than the corresponding spine of califor- nicus. The adoral member is about as long as the furrow spine which stands vis-a-vis. Outer or second actinal series usually consists of 3 slender untapered spines somewhat shorter than furrow spines, and standing in a fairly regular row. Near base of furrow 2 or 3 very small spinelets sometimes stand on outer end of plate. Mouth spines similar to those of californicus, but the mar- ginal series stand slightly spaced from the intermediate spines, so that inner end of combined plates is broader and the 3 series, superficial, intermediate and marginal, are more clearly evi- dent. All spines are slenderer and a trifle longer than in cal- ifornicus. Marginal spines, about 7 between tooth and inner end of first adambulacral plate ; and about 6 or 7 more minute spinelets continue the series two-thirds distance to outer end of plate. Madreporic body concealed by paxillae, situated as in cali- fornicus and crossed by sinuous strias ; tiny, spiniform knobs on ridges of californicus apparently lacking. Color in alcohol, bleached yellowish to whitish ; color in life unknown. Type, No. 21927, U. S. Nat. Mus. Type locality, vicinity of Santa Barbara Islands, in 150 fathoms. The vertical range is 67 to 162 fathoms, and the species extends south to Lower California at least, and north to the latitude of Monterey Bay. Remarks. — This species differs from A. fragilis Verrill in having numerous actinal adambulacral spines and shorter rays. NEW STARFISHES FROM THE PACIFIC COAST 121 A. regalis Gray, a short-rayed form, also has but one actinal adambulacral spine, scarcely longer than longest furrow spine. A. vcrrilli de Loriol differs from ornatissimus in having a dif- ferent inferomarginal and adambulacral armature. The supero- marginal plates of verrilli carry small tubercles forming a single longitudinal series. A. rubidus de Loriol is allied to articulatus (Say), having broad supermarginal plates, a smaller disk than ornatissimus^ and with rays broader at tip, paxillae with shorter spinelets, and adambulacral plates with much smaller spinelets — 3 small ones in actinal ser Family LUIDIID^ (Sladen) Verrill. Genus Luidia Forbes. Luidia Forbes, Mem. Wern. Soc, vni, 1839, I23* There are three species of Luidia occurring off the California coast. In literature two names occur — Luidia foliolata Grube ' and L. catifornica Perrier.2 According to Ludwig the latter name is a nomen nudum ; hence it need not further be con- sidered. Ludwig3 further states that Grube gives California as the locality of foliolata. I have not been able to consult Grube's description, but from the fact that Sladen thinks folio- lata may not be distinct from brcvispina, I have considered that the name must apply (if not actually to brcvisfina) to a common, shallow water Luidia (Southern Alaska to San Diego, and Mazatlan?) which is closely related to brevisfiina. This- form I have compared with specimens of L. brcvispina, and it is perfectly distinct. If the name foliolata does not apply to it, it is a new form. The other 2 species are evidently new and the more evident characters of the 3 forms are contrasted in the following synopsis. 1 L'eber einige neue Seesterne des Breslauer zoologischen Museums < 43 Jahresber. d. Schlesisch. Gesellsch. f. vaterland. Kultur, Breslau, 1S66, 59. {Fide Ludwig.) 2 Etude sur la repartition geographiques des Asterides. < Xouv. Archiv Mus. Hist. Nat. Paris, II ser. I, 1S7S, $■;, 91. (Fide Ludwig.) 3 Mem. Mus. Corhp. Zool., XXXII, 1905, So, footnote. 122 FISHER a. Lateral abactinal paxillae with a quadrate or subquadrate tabulum. b. No pedicellariae ; abactinal surface drab gray or greenish gray in life Luidia foliolata . bb. Pedicellariae (bivalved) on inferomarginal plates (abactinal end) and on superomarginal paxillae, and trivalved upright pedicel- lariae on actinal intermediate plates ; abactinal surface reddish in life, sometimes mottled with lighter Ltiidia ludivigi. aa. Paxillae with stellate crown ; granuliform abactinal 2-jawed pedi- cellariae; slender 2-jawed actinal intermediate pedicellariae; rather prominent lateral spines Luidia asthenosoma. LUIDIA LUDWIGI Fisher, new species. Rays 5. jR = 107 mm.; r = 13 mm. 7? = 8.2r. Breadth of ray at base, 15 mm. Rays slender, very gradually tapering to a pointed extremity ; interbrachial arcs acute ; general form depressed as in other species of genus, but abactinal surface well arched ; sides of ray rounded ; abactinal area with 3 or 4 regular series of quad- rate paxillae on each side, the superomarginal with small 2- and 3-jawed pedicellariae ; inferomarginal plates rather narrow, arched, with 1 to 3, usually 2, lateral spines, and 3-6 actinal spinules larger than spinelets of general surface, and on upper end a pedicellaria similar to that of adjacent paxilla ; actinal intermediate plates of interradial areas and proximal half of ray each with a rather prominent 3-jawed pedicellaria ; adambula- cral plates with a curved furrow spine, 3 actinal spines and 1 or 2 smaller spinules. Abactinal paxillar area rather crowded ; paxillae of 4 or 5 lateral regular series, quadrate ; fourth, fifth, or sixth series (according to size of specimen) with many subcircular or not obviously quadrate paxillae ; superomarginal paxillae slightly smaller than those of adjacent series ; paxillae thence decreas- ing in size toward mid-radial area where they are arranged without regularity and are roundish or irregular in outline. In some small specimens paxillae are not so obviously quadrate in lateral series, being subcircular in outline, but nevertheless arranged regularly. Crown of spinelets not so flat as in folio- lata but rather convex especially in small examples ; supero- NEW STARFISHES FROM TIIF PACIFIC COAST 1 23 marginal paxillae with about 35 short clavate spinelets in a radiating coordinate group, and most of them also with a small 2-jawed valvate pedicellaria, slightly longer than spinelets ; next series with about 40 spinelets, those in center of tabulum stouter than the peripheral, as in superomarginal paxillae ; small mid-radial paxillae with about 20 spinelets. Inferomarginal plates relatively narrower than in foltolata (i.e., with reference to transverse axis of plate); fasciolar grooves deep, and wider (with reference to long axis of ray) than same dimension of special raised ridges of inferomargi- nals. Outer or abactinal end of each plate with a 2-jawed pedicellaria similar to that of adjacent superomarginal paxilla, and with 1 or 2, usually 2, tapering sharp spines, of which sometimes the inner, sometimes the outer, is the longer; the longer (about 4 mm.) equal to about width of its plate; more rarely 3 shorter subequal spines in transverse series on outer end of plate ; spines forming a prominent marginal fringe to ray ; on actinal surface of plate, 3 to 6 much shorter spinules form a transverse series in line with lateral spines, or a zigzag, or even double series, while margin of plate bears slender terete spinelets, becoming more capillary in fasciolar grooves. Adambulacral armature consisting of a curved sabre-shaped furrow spine, and on actinal surface 3 tapering bluntly pointed spines, of which 1, the longest, stands behind furrow spine and the other 2 forai a slightly oblique longitudinal series just behind first actinal spine ; or 2 spines, the adoral the shorter, stand in a longitudinal series just behind furrow spine, and the third just outside of the aboral (longer) spine of the series ; 1 to 3 small slender spinelets occur on outer part of plate, frequentlv 3 at base of ray forming a longitudinal series, or 1 on adoral edge of plate, back of outer adoral spine. Actinal intermediate plates of interradial region and proximal half of ray paxilliform, surmounted by a prominent 3-jawed pedicellaria which is surrounded at base by numerous slender spinelets in a calyx-like whorl. Each pedicellaria is conical and 1.5 to 2 times as high as its width at base. Mouth plates narrow, with 6 or 7 marginal spines and 7 or 8 superficial ones, forming together a double series on the raised 124 FISHER exposed surface of plate parallel with median suture. Inner spine of superficial series largest, and like the rest, slender, pointed, tapering. All spines decrease in size toward outer end of plate. Innermost marginal spine situated nearer peri- stome than is the enlarged inner superficial spine. Madreporic body between second and third lateral rows of paxillse, and hidden by them. Type, No. 21928, U. S. Nat. Mus. Type locality, Alba- tross Station 2970, vicinity of Santa Barbara Islands, in 29 fathoms, on fine gray sand and mud. Remarks. — This species has the general form of L. lorioli Meissner (Mazatlan), but has longer arms, which are more at- tenuate distally. L. ludwigi lacks the conspicuous sharp spinules which are present in many of the lateral abactinal paxillse of lorioli, and the latter has no abactinal pedicellariae, such as are very characteric of the present species. Another character which separates ludwigi from both lorioli and bellonce Lutken is the presence of prominent pedicellariae on the actinal inter- mediate plates of interradial region and proximal half of ray. Details of adambulacral armature differ in all three forms. L. ludwigi differs from L,. quinaria in having much longer nar- rower rays, no scattered and abundant abactinal pedicellariae over the midradial region, and in having 3-jawed, not 2-jawed, actinal pedicellariae. The abactinal pedicellariae of quinaria are low, and of the bivalved form of some Goniasteridae. The adambulacral plates also have 2-jawed pedicellariae in quinaria. Named for Prof. Hubert Ludwig. LUIDIA ASTHENOSOMA Fisher, new species. This fragile creature bears a close resemblance to L. sarsi Diiben and Koren, of northern Europe and the Mediterranean, and may be looked upon as a north Pacific representative of that species. None of the specimens are as large as L. sarsi is known to grow. The California species differs from sarsi in having very small, abactinal, 2-jawed (rarely 3-jawed), gran- uliform pedicellariae scattered along the medioradial area, with larger ones, sometimes, on the regular lateral paxillae, and on upper end of inferomarginal plates. The inferomarginal spines NEW STARFISHES FROM THE PACIFIC COAST 1 25 are longer, the adambulacral armature and minor details of paxilla? are different. Rays 5. 7?= 86 mm.; r = 9 mm. ; 7? = 9.5/-. Breadth of ray at base, 10 to 11 mm. Rays long, narrow, pointed, very gently tapering, with a slightly convex abactinal surface usually sunken along mid- radial line. General form much flattened ; sides of rays rounded ; inferomarginal plates narrow, not encroaching much upon actinal area, but forming rather the margin of ray ; ambu- lacral furrow wide and shallow ; tube feet long, in 2 series ; actinal and marginal spines rather long and bristling, the ad- ambulacral armature forming 2 series continuous with that of inferomarginal plates; actinal intermediate plates usually with a rather short, 2-jawed, blunt, papilliform pedicellaria. Abactinal paxilla? with a stellate crown ; those of supermar- ginal series larger than rest, and each corresponding to an infero- marginal plate, to upper end of which it is closely juxtaposed. Crown of superomarginal paxilla longitudinally oval (as in sarsi), the others subcircular. Adjacent to superomarginal paxilla? are about 2 regular series of lateral abactinal paxilloe, about 2 of which correspond to 1 superomarginal paxilla. Paxillae diminish in size very rapidly toward median line of ray and become less regular in arrangement as they approach it. Superomarginal paxilla has slightly convex tabulum armed with about 30 slender denticulate spinelets, of which about 10 are scattered on surface of tabulum and the remainder about the periphery, the whole forming a diverging group. The superomarginal and other lateral paxilla? sometimes have a blunt 2-jawed pedicellaria similar to but larger than those scat- tered over the midradial area (see below). The adjacent pax- illae have about 12 peripheral and 3 to 5 central spinelets, while those in midradial region have about 10 peripheral and 3 or 4 central, very much smaller, spinelets, the whole paxilla being notably smaller. Many of small paxilla? of midradial area also bear in center of tabulum, surrounded usually by a few small peripheral spinelets, a small obovoid 2-jawed valvate pedicel- laria, resembling a split granule. Viewed from above, the pedicellaria is elliptical in shape when closed. Each jaw is 126 FISHER hollowed on inner face and occasionally is larger, springing from a very low paxilla and emerging between the others. Rarely there are 3 jaws. Jaws of pedicellariae much thicker and more robust than any paxilla spines. Inferomarginal plates relatively very narrow, transversely arched, encroaching but slightly upon actinal surface, forming rounded margin to ray; chord of width equal to 1.5 times that of adambulacral and actinal intermediate plates combined. Fasciolar grooves deep and wide, slightly wider (/. e., meas- ured on long axis of ray) than corresponding dimension of specialized elevated ridge of plate. Each plate with a trans- verse series of 3 robust, tapering, sharp spines, of which the outer is often slightly the longest, but frequently the middle one, or the 2 are subequal ; inner (actinal) spine of series is some- times much slenderer than other 2, and only one half or two thirds length of longest spine ; latter attains a length of 5.5 mm. or slightly over one half width of abactinal paxillar area, or nearly twice width of plate (/. Bot. Mag. Tokyo 15 : (92). 1901. 17: (38). 1903. 2Nova Acta Acad. Cajs. Leop. -Carol. 83. 1905. EXPLANATION OF PLATE VI. Metzgeria quadriserzata Evans. Fig. i. Part of thallus, just beyond a fork, postical view, X 40. 2. Midrib with adjoining cells, antical view, >( F>°- 3. Marginal cilia, X 225. 4. Cross section of midrib with adjoining cells, postical edge below, X -~^- 5. Female branch, X 4°- The figures were all drawn from the type specimen. Radirfa oya?ncnsis Stephani. Fig. 6. Part of female plant with perianth and subfloral innovations, postical view, X 17- 7. Part of stem, antical view, X *7- 8. Cells from middle of lobe, some of the verrucuhe showing at right, X3°Q- 9. Apex of lobule, X 225. 10. Pericha;tial bract, X 4°- The figures were all drawn from Okamura's specimens. Lcjcunca planiloba Evans. Fig. 11. Part of female plant with perianth, postical view, the lobule of a bract lying over the stalk of the capsule, X 40. 12. Part of stem, postical view, X 4°- 13. Cells from middle of lobe, X 300. 14. Apex of lobule, X 225. 15. Bract with connate bracteole, X 4°- 16. Other bract from same involucre, X 4°- The figures were all drawn from the type specimen. ' [62 Proc Wash. Acad Set., Vol. Vl!l. Plate VI. FIGS 1-5, METZGERlA QUAORISERIATA EVANS. FIGS 6-10. RADULA OYAMENSIS STEPHANI. CIGS 11-16. LEjEUNcA PLANILOBA EVaNS EXPLANATION OF PLATE VII. Leptolejeimea subacuta Stephani. Fig. i. Part of female stem with two inflorescences, postical view, X 4°- 2. Part of stem with branch, postical view, X 4°- 3. Propaguliferous branch with one propagulum about to be separated postical view, X 4°- 4. Cells from middle of lobe, the middle cell an ocellus, X 3°°- 5. Apex of lobule, X 225. 6. 7. Underleaves, X 225. 8. Bracts and bracteole with subfloral leaf and underleaf, X 40- 9. Bracts and bracteole from another involucre, X 4°- The figures were all drawn from the type specimen. D repanolej eunea tenuis (Reinw. Bl. & Nees) Schiffn. Fig. 10. Part of female plant with perianth, postical view, X 4°- 11, 12. Parts of stems, antical view, X 4°- 13. Cells from middle of lobe, X 3°°- 14. Cells from antical margin of lobe, X 225- 15. Apex of lobe, X 22S- 16. Apex of lobule, X 225. 17. 18. Underleaves, X 225- 19. Bracts with connate bracteole, X 40. Figs. 11 and 12 were drawn from specimens collected by Tevsmann in Java and determined by Gottsche ; the others from Okamura's Japanese specimens. (164) Proc Wash. Acad Sci., Vol viii. Plate vii FIGS. 1-9. LEPTOLEJEUNEA SUBACUTA STEPHANI. FIGS. 10-19. DREPANOLEJEUNEA TENUIS (REINW. Bl. & NEES) SCHIFFN. EXPLANATION OF PLATE VIII. Uarpalejeunca i?iter?nedia Evans. Figs. 1,2. Parts of female plants, each with an inflorescence, postical view X40. 3. Part of stem, antical view, X 4°- 4. Cells from middle of lobe, X 3°°- 5. Cells from antical margin of lobe, X 225- 6. Apex of lobule, X 225. 7. Underleaf, X 225. 8. 9. Apices of underleaf-divisions, X 225- 10. Bract with connate bracteole, X 4°- 11. Other bract from same involucre, X 4°- The figures were all drawn from the type specimen. Frtdlania denslloba Stephani. Fig. 12. Part of female plant with perianth, postical view, X 4°- 13. Part of stem with bases of 2 branches, postical view, X 4°- 14. Part of stem with base of branch, antical view, X 4°- 15. Branch with limited growth and crowded lobules, postical view, X 40. 16. Cells from middle of lobe, including one ocellus and part of another, X3°°- 17. Stylus of stem-leaf, X 225. iS. Apex of one division from a stem-underleaf, X 225- 19. Branch-underleaf, X225. 20-22. Innermost bracts and bracteole from a single involucre, X 4°- Figs. 12, 20, 21 and 22 were drawn from the type specimen ; the others from Okamura's specimens. (166) Proc. Wash. Acad Sci., Vol. VIII. Plate VIII. FIGS. 1-11. HARPALEJEUNEA INTERMEDIA EVANS. FIGS. 12-22. FRULLANIA DENSILOBA STEPHANI. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 167-196. December 18, 1906. A STUDY OF RHUS GLABRA. By Edward L. Greene. INTRODUCTION. The genus Rhus as Tournefort restricted it two centuries ago, and as many another systematist since his day has held it, is clearly marked and easily denned. As to habit — that foremost indication of a good plant genus — this generic type stands well aloof from all its allies ; even distinctly apart from each and every one of those kindred generic groups which, like Cottnus, Toxicodendron, Metofiium, Lobadium, Rhoeidium, and Styftho- nia, in another than the Tournefortian school of taxonomy, have been thought of as preferably constituting mere subgenera of RInts. But not a species in any of those other genera named makes the least approach to typical Rhus in habit. Every species and variety of this appears as a shrub or tree with few stout stag- horn-like branches, each clothed heavily near its summit with odd-pinnate leaves, these usually large and of many leaflets. In our silva the only tree which in aspect recalls the sumachs is that naturalized alien, the Ailanthus, a genus 01 no near affinity to Rhus. But between the last and its near relative Schmaltzia there is no habital resemblance. In this regard they are quite as unlike as are currant bushes and elder trees ; and, as for Toxicodendron, its habit is as remote from that of Rhus as the habit of a grape vine or English ivy is remote from that of wal- nut trees. Over and above its marked habit, the characters by which this Rhus of Tournefort establishes itself as a model genus are, the Proc. Wash. Acad. Sci., December, 1906. 167 l68 GREENE terminal origin of its inflorescence, the firmness and compactness of that inflorescence, concurring with small red velvety or plushy drupelets for fruits. Of the genus, in this which seems to me the most reasonable and natural acceptation of it, there exist in North America, ac- cording to classic standards, four species, — Rhus glabra, typhina, ptimila and copallina} To the last of these there is attributed a geographic range somewhat incredible for that of any one species of shrub of what- ever genus ; almost incredible, I say, to any experienced student of climatology as affecting plant life and the distribution of spe- cies. But according to the books Rhus copallina occurs as one and specifically the same in several widely sundered and very different floral regions. It is said to be common in the hard soil and severe climate of New England, and as much at home in the subtropic lowlands of Florida, twelve hundred miles southwest- ward ; even running away to the arid cactiferous hills of further Texas that lie westward from Florida another thousand miles ; and yet again, in a region so extremely different from either of these as that of the Great Lakes in Minnesota and Wisconsin, the same Rhus copallinay it is said, recurs. An European celebrity more than twenty years ago, without field knowledge of the shrubs, and with no experience in prob- lems of North American phytogeography, but using the imper- fect light of European herbarium material only, made out and named a half dozen varieties and subvarieties of our Rhus copal- Una;"1 all which work is ignored or suppressed by later Ameri- can compilers of books ; to whom the following out of the vivid suggestions of Engler would entail the expenditure of much time and energy, whereas suppression is of all things the most easily done. Rhus copallina is one of many hundreds of North American phytologic problems awaiting investigation and solution. Another of our four species, namely Rims pumila, stands in most marked contrast to the preceding in point of geographic LTorrey & Gray, Flora of North America i : 217. Gray, Synoptical Flora 1 : 384- 2 Engler, in DC. Monographic Phanerogamarum, 4: 3S3. A STUDY OF RHUS GLABRA 169 distribution. It is almost local, occurring nowhere but in lower and middle districts of the Carolinas and Georgia. Rhus lyphiua, the largest and most tree-like of our species, ranges widely, at least when compared with R. pumila. It is cata- logued for all the states from Maine to Georgia and Mississippi, thence northward to Minnesota and the Dakotas, but is every- where less common than R. glabra, and more particular than either that or R. cofalliiia as to its environment. Everywhere southward it is of the mountains or the hill country only, never coming down to the lowlands or to the seaboard. Neither at the northwest does it come out from its woodland habitat to adorn the copses bordering the prairies where a subspecific ally of R. glabra is so much in evidence. It seems to have little adaptability to varying conditions other than those of heat and cold ; though in this regard its adaptability is very marked. The climate of Minnesota and the Dakotas, and that of Georgia and Mississippi are extremely unlike as to temperature. Yet between the Julius typhina of the most northerly locality and that of the stations farthest southward, one does not discover notable differences other than those of the size of the shrub and the number of the leaflets. In other respects they seem to be much the same ; so that the type is apparently one of a singular degree of stability under somewhat varying conditions. Concerning R/ius glabra, the type species of the genus as to North America, one may note first of all its nearly universal dis- tribution. In this regard it is most unlike any of its congeners here. From beyond the river St. Lawrence northward, down, to the very shores of the Gulf of Mexico, its range is across the continent. Within these parallels, into every floral region be- tween the oceans, however different — excepting only that of California — there enters that which, according to the books and lists of plants, is Rhus glabra. There is no one species of tree or shrub of any continent that really holds the geographic range which the books and lists ascribe to Rhus glabra. By all the analogies of things there ought to be several marked species or subspecies of this type in the southern Appalachian region between Maryland and Ten- nessee and Georgia ; another and an equally distinguishable set iyo GREENE between northern New England and the headwaters of the Mississippi beyond Lake Superior ; another species or two pecu- liar to that vast empire of the Middle West, the prairie country ; as many more in that different and equally extensive stretch of country lying between southern Missouri and the shores of the Gulf of Mexico. Then, since there is a Rhus glabra all up and down the two thousand miles' length of the Rocky Mountain region, this ought to be thoroughly distinct by plenty of charac- teristics, and to resolve itself naturally into a number of varieties or subspecies. Just the same should be looked for in the shrub accredited to another empire, that of the Pacific slope northward lying between the sources of the Columbia and Puget Sound; while the scores of isolated mountain ranges rising up out of the deserts of Nevada, Utah, Arizona and New Mexico — for the type in question is there also — should furnish another and pre- sumably the most marked group of Rhus glabra segregates. Our herbaria cannot to-day be supposed to be well supplied with specimens representing this type. No author has investi- gated it, and no special call has been made for the collecting of these shrubs from different regions. Nevertheless, the mass of material that has been before me during some months past is amply sufficient to enable the investigator to point out characters by which a number of species may be, and reasonably must be, given recognition ; characters of foliage in abundance, and characters of the fruiting panicle and the fruit itself. Perhaps more trying than the task of examining and com- paring specimens to find out specific characters, is the great amount of bibliographic work that is necessary in order to determine which one of the several eastern species ought to bear the name Rhus glabra; for even this, as indicated — though never described — by Linnaeus was an aggregate. In the botanic gardens of Europe several species had been long in cultivation, had been recognized as species and even described as such, when Linnaeus in the middle of the eighteenth century came along, and, bundling all the glabrous kinds together, named not any one of them, but the whole bundle of species, Rhus glabra. If Linnaeus is to be credited with some one particular Rhus A STUDY OF RHUS GLABRA 1 7 1 glabra that we must if possible segregate from the bundle of species which bundle he so named, our task is one demanding the very best skill of both the taxonomist and the historian. EARLY HISTORY. Prior to the discovery of America the Rhus of all botany was a monotypic genus. It began and ended with Rhus carta)/ a, also by some authors called Rhus obsoiu'oruui, a shrub of the Mediterranean region, well known in the useful arts from im- memorial ages. No second species of Rhus was known until as late as the year 1620, when Caspar Bauhin, publishing an illustrated quarto containing names and descriptions of more than 600 new plants from various parts of the world, brought to the notice of bot- anists what he chose to name Sumach angustifolium} This was known to have come from the New World, though in an herbarium specimen only. Historically this is the earliest and oldest element entering to the confused R. glabra Linn. Bauhin himself in the year 1620 showed a preference for the Arabic name Sumach, the exact equivalent of the Greek and Latin Rhus ; but in his more comprehensive work of three years later, the Pinax, as if having decided to use the Greek and Latin rather than the Arabic name of the genus, he adopts Rhus, renaming his new American species, Rhus augustifolia? At the time of its publication in 1620, and long afterwards, the material on which it was founded was believed to have been derived from some island off the coast of Brazil ; but a century later, no further specimens of it having been received from any part of South America, and because of its now having come to be known as certainly North American, the idea of its being indigenous to Brazil was abandoned. In so far as I have been able to examine early records, the next mention of any American Rhus is in Banister's Catalogue of Virginian Plants, published in the year 1688. That this was some member of the group of R. glabra we are assured by his note that the branches are glabrous. The one with soft hairy 1 Prodromus Theatri Botanici, p. 15S. 2Pinax Theatri Botanici, p. 414. 172 GREENE branches, R. tyfihina, was by this time well known by Bauhin's description of it, and had perhaps already appeared in some gardens in Europe. In 1726 both the hairy and the smooth sumachs were to be found in some London gardens and parks, and in 1732 Dillenius published a folio plate and a full descrip- tion of what must apparently stand for the R. glabra Linn, of 1753- CHARACTERS FOR SEGREGATE SPECIES. Linnaeus' statement of the characters of Rhus glab?'a reads thus : " Leaflets pinnately arranged, lanceolate, serrate, glabrous on both faces." This is the same as no description at all. If one assume said compound leaf to be odd-pinnate rather than equally pinnate, one does so without any warrant in any word that author said about either the species or the genus. Equally without warrant will be any assumption that the leaf is of 7 leaflets, or that it is of 17, or of 27. Linnaeus gives no hint of its character in these most significant particulars. One will also reasonably infer that the leaflets are not notably pointed at the upper end ; and whether at base they be stalked or sessile you have no means of judging. It must also be assumed that there is no distinction of coloring noticeable respecting the two faces of the leaf; also whether of a dark-green, or of a bright-green, or of a glaucous or blue-green, one is not informed. Such a description as Linnaeus gives of Rhus glabra might easily apply to each one of five species, or of fifty, or of five hundred species in a genus. It is therefore worthless for diagnostic purposes. Coming down from the middle of the eighteenth century to near the close of the nineteenth, we shall find that in American books of American botany the Linnaean diagnosis of R. glabra has met with a little amendment. That in Gray's Manual in 1890 reads thus : " Smooth, somewhat glaucous ; leaflets 11-31, whitened beneath, lanceolate-oblong, pointed, serrate." The expression, " whitened beneath," is one that helps us to fix on certain shrubs, mostly southern, as representing this author's R. glabra; but in New England there are at least two different sumacs which this phrase completely excludes ; one of them, inhabiting Massachusetts, shows not even a trace of bloom on the lower face. Both of these, and with them several more A STUDY OF RHUS GLABRA 1 73 species of the east and south, are excluded as having hardly half of the " 11-31 " leaflets. In Britton's Manual of 1901 is that of Gray somewhat ampli- fied and therefore less safe. Here Gray's evasive term, " pointed," gives place to the more definitive word " acumi- nate," but this excludes yet another set of forms in which no leaves are acuminate. Moreover, leaves and leaflets have dif- ferent ways of being acuminate, in so much that, in order to be able to really describe the apex of the leaflet in each segregate of R. glabra, I find it necessary to use such truly definitive terms as subulate-acuminate, cuspidate-acuminate, and such phrases as slenderly acuminate and caudately acuminate. But more unfortunate still is the Britton's Manual description of the leaves as being dark-green above. That indeed applies to what I take for real R. glabra, and to several of its Atlantic slope allies ; but it holds good in not one of those far-southwestern species of New Mexico, Arizona and Utah, which said Manual goes far out of its way to speak of as forming a part of R. glabra. Even in the middle west and far-northwestern districts not a tithe of the definable species can be said to have leaves of other than a dull lightish green. Finally, the authors of none of the books knew anything of the differences of fertile inflorescences in this aggregate. That these in the fruiting and mature state are narrowly oblong in a few, oblong-fusiform in many, and almost or quite exactly pyramidal in many more, a discovery the importance of which will not be disputed, is a fact which is herein first brought to notice. It is my belief that even the flowers in some species will be found to present characters available for the further establish- ment of species here. Both calyx and corolla are far from being the same in all ; but I have declined to make any use of these for the reason that in the herbaria exist such multitudes of specimens that are in flower only, and of which the fruiting panicles are yet unknown. In true Rhus glabra, and also in by far the greater propor- tion of the segregates herein proposed, both branches and foliage are wholly glabrous. In the diagnoses I permit this to be taken 1 74 GREENE for granted, never mentioning such a matter except in the cases of those two or three of the new species in which there occurs a trace of pubescence. Key to the Species. * Leaves deep or dark green above (except in Xo. 9), usually white with bloom beneath, f Panicles of fruit oblong, or oblong-fusiform. Leaflets very many, 17—21 or more, and large. Leaflets oblong-lanceolate, obtuse at base and subsessile, at apex abruptly pointed 1. R. glabra. Leaflets oblong-lanceolate, sessile, slenderly long-pointed. 2. R. oreophila. Leaflets linear-lanceolate, sessile and auricled at base, at apex caudate-acuminate. 3. R. auriculata. Leaflets less numerous, commonly 13-17. Leaflets lance-oblong, tapering abruptlv at base and less abruptlv at apex 4 . R. tthacensis. Leaflets oval to oblong-lanceolate, merely acute at apex. 5. R. ashei. tt Fruiting panicles broadest near the base and pyramidal. Leaflets rather few (except in Nos. 6 and S). Leaflets 17-21, sessile, oblong-lanceolate, acuminate. 6. R. pyramidata. Leaflets very large, but only 13-17, subsessile, acute rather than acuminate 7. R. caroliniana. Leaflets 19-23, narrowly oblong-lanceolate, obtuse at base, the apex subulate-linear S . R . atrovirens . Leaflets 13-17 and small, oblong-lanceolate, coarsely serrate, slend- erly acuminate 9. R. ptdchella. Leaflets only 11-15, notably thin, attenuate-acute. 10. R. ladoviciaiia . Leaflets 11— 13, small but firm, subpetiolulate, abruptly but sharply acuminate.. 11. R. arbuscula. Leaflets 13-15, large, petiolulate, subfalcate, sharply acuminate. 12. R. petiolata. Leaflets 13-17, oblong-lanceolate, subpetiolulate, triangular-subulate at apex 13. R. valida. Leaflets 13-15, sessile by a rounded base, the apex short, slenderly attenuate 14. R. longula. Leaflets only 11-13 and small, sessile, subulate-acuminate, their rachis pubescent 1^. R. sandbergii. A STUDY OF RHUS GLABRA 1 75 * * Leaves ample (except in No. 25), of a lighter green above, less glaucous beneath. Panicles in almost all pyramidal. All the species far western and northwestern. Leaflets 13-17, subsessile, sparsely pilose, subulate-acuminate. 16. J\ . borealis. Leaflets 1 1— 1 3. Large, sessile, subfalcate-oblong, abruptly broad-pointed. 17. R. media . Oblong, subsessile, abruptly acuminate iS. R . cismontana. Large, acutish at base and subpetiolulate, abruptly short-pointed. 19. R. sambucina. Leaflets 13-17- Shining above, sessile by an obtuse base, cuspidately acute. 20. R. miens. Checkered light and dark green above, subsessile, cuspidatelv acu- minate 21. R. tcsscllata . Leaflets 9-15, oblong-lanceolate, sessile, acuminate. 22. R. macrotkyrsa. Leaflets 17-19, oblong-linear, sessile, acutish at base, long-acuminate. 23. R. arguta. Leaflets 13-17, oblong, sessile, obtuse at base, the apex merely acute. 24. R. aprica. Leaflets 11-13, narrowly lanceolate, sessile, acuminate. 25. R. occidentalis . * * * Leaves smaller, of fewer leaflets, altogether pale, very glau- cous beneath. Panicles small, less definitely pyramidal. All of arid southwestern regions (But Xo. 9. A'. pnl- chclla, of the southern Appalachian mountains is naturally of this group). Leaflets 1 1-15. Sessile, oblong-lanceolate, short-acuminate 26. R. albida. Petiolulate, subfalcate-lanceolate, slenderly acuminate. 27. R. elegant id a. Leaflets 9—1 1 , sessile, oval to oblong-lanceolate 2S. R. sorbifolia. Leaflets 7-9, subsessile, lanceolate, slenderly acuminate deeply incise- serfate 29. R. asplenifolia. 1. RHUS GLABRA Linnaeus. Rhus rami's ex stipitc -pullulantibus giabn's, Banist. Catal. in Ray, Hist. 2 : p. 1928. 1688. Rhus Virginicum panicula sparsa, rami's patulis glahris, Dillen., Hort. Elth. p. 323, t. 314. 1732. 176 GREENE Rhus glabra Linn. Sp. PL, p. 265. 1753, in part, excluding both the shrub of C. Bauhin and that of Catesby. Rhus glabrum, Mill. Diet. 1768? Shrub commonly 2-3 m. high, with very few and stout diver- gent branches: leaves mostly 5-7 dm. long, the rachis and petiole very stout, the latter 1-1.5 dm. long; leaflets about 17-21, not crowded, very large, 8-13 cm. long, 3-3.5 cm. wide, oblong-lanceolate, subsessile, abruptly and not slenderly acumi- nate, evenly serrate, the serratures 12 or 13 on a side, texture in maturity rather firm but not subcoriaceous, upper face deep green and smooth, lower face glaucous but not excessively so : staminate panicle very large, often 3 dm. high, pyramidal, almost 2 dm. wide at base in the largest, the pistillate, when in flower nearly as long but fusiform, less than 1 dm. wide up and down the middle part, in fruit oblong-fusiform, 6-10 cm. wide below the middle ; drupelets very many, round-ovate. This is the common and apparently the only glabrous Rhus of the Potomac Valley in southern Maryland and eastern Vir- ginia, ranging eastward and northward through southern Pennsylvania, to Delaware, New Jersey, and to Connecticut, if I refer here a flowering specimen in the National Herbarium from Green's Farms, 1894, by C. L. Pollard. The type from which the above description is drawn is the shrub as it grows in the District of Columbia, and up and down the Potomac above Georgetown. The choice between this and the next for something to bear the name R. glabra Linn, is made rather arbitrarily, perhaps ; for either one may have been that grown in the Eltham garden and figured by Dillenius. The two are distinct by their fruiting panicles, and the fruit of the Dillenian type was unknown, because only the staminate shrub was raised from the seed by which it was introduced into Europe. As to the size of the leaves and leaflets, however, the present species alone answers to the account given by Dillenius ; hence the probability in favor of this as identical with his. Since Linnaeus himself did not describe the species ; and since the one only synonym, quoted by him which carries with it a description is that of Dillenius, the name R. glabra must be A STUDY OF RHUS GLABRA 1 77 applied here unless it be left to fall into synonymy altogether. Philip Miller, as a contemporary of Dillenius and Linnaeus, and as a cultivator of these shrubs, might have been expected to identify correctly the A', glabra of Linnaeus when he adopted the name ; yet to what he so named in his Dictionary, the name glabra does not really apply, for he describes its branches as downy, thus awakening a doubt as to whether his R. glabra was not some possible segregate of Rhus typJiina. 2. RHUS OREOPHILA, sp. nov. Shrub 2-3 m. high : leaves 3-4 dm. long, the petiole 6-8 cm. long : leaflets 19-27, closely approximate, not of the largest, 7—9 cm. long, 2.5 cm. wide, narrowly oblong-lanceolate, sessile, rather slenderly acuminate, lightly and almost obsoletely ser- rate, the serratures 10-12 on each side, texture firm, almost subcoriaceous, lower face whitish with a dense bloom, upper face by no means deep or dark green, of a rugulose-roughened rather than smooth surface : fruiting panicle large and much elongated, oblong-fusiform, 18-28 cm. long, only about 5 cm. wide, very compact, the drupelets subglobose, nearly 5 mm. in diameter. Mountain districts of Maryland, Virginia, the Carolinas and eastern Tennessee ; not in the lower hill country of the Potomac Valley outside the mountains, nor at all northward. The type specimen in the National Herbarium is on sheet No. 327800, from Chapel Hill, North Carolina, by W. W. Ashe, no date of collecting given, nor any specific locality. Two sheets from the Biltmore Herbarium, the material gathered at different dates in 1896 and 1897, without indication of either the collector or special station, except the name Biltmore, represent the species beautifully. So does another, from the mountains of Cocke County, Tenn., by Mr. Thos. H. Kearney, September 14, 1897. Yet another U. S. Herbarium specimen, in good foliage but young fruit, is from near Luray, Va., by Mr. and Mrs. Steele, August 30, 1 901. The species is in contrast with R. glabra by smaller leaflets, with denser bloom beneath, and a longer, narrower thyrsus of larger and more closely compacted drupelets. I78 GREENE It may not perhaps be determinable to a certainty that the preceding rather than this, was grown in London, and formed the type of Dillenius' figure of leaves and staminate panicle. But Banister's field, and probably that of Catesby also, by both of whom seeds were sent to England, was the lower country, where only what I have here called Rhus glabra is found. 3. RHUS AURICULATA, sp. nov. More slender than R. glabra, all the parts somewhat smaller, the fruiting panicles especially only about one-third as large : leaves 2.5-3.5 dm. long; leaflets about 19, approximate, often alternate, 7-10 cm. long, never more than 2 cm. in width, often less, of linear-lanceolate outline, the apex caudately long-atten- uate, the sessile base showing definite though small auricles, the serratures light but rather close, 14-18 on a side, texture subcoriaceous, the upper face light green, transversely rugose, the somewhat sunken veins correspondingly prominent on the very glaucous lower face ; fruiting panicles oblong or slightly verging toward the pyramidal, 10-13 cm' high 5 drupelets com- paratively few, large. A remote southwestern ally of R. glabra, with very definite specific marks. It is known to me only as collected by Mr. C. L. Pollard, August 11 to 12, 1896, the special locality, Agri- cultural College, Oktibbeha County, Mississippi. The type specimen occupies sheet 271931 of the National Herbarium. There is a duplicate in Herbarium Field Museum which I have seen. Mr. Pollard's distribution number 1261 is on these two of his labels that I have seen. The species must quite surpass R. glabra in beauty. Its narrow slender-pointed leaflets seem to droop from the rachis rather than to spread away from it horizontally. This, how- ever, is characteristic of several other allies of R. glabra belong- ing to regions lying westward. 4. RHUS ITHACENSIS, sp. nov. All the parts smaller and more slender than in R. glabra, the branches not glaucous, seldom glaucescent : leaflets 13-17, A STUDY OF RHUS GLABRA 1 79 sessile by an abruptly acutisb base, 6-7 cm. long, saliently serrate, tbe serratures 13-15 on a side, upper face dull deep green, lower glaucous but less so than in R. glabra, the texture thinner: fruiting panicle small comparatively, long-peduncled, 12-18 cm. long, oblong fusiform, not very compact, its branches thinly tomentellous ; drupelets below medium size, notably smaller than in R. glabra. Seems to take the place of R. glabra everywhere to the west- ward of the Alleghenies in western Pennsylvania and New York, and in northern Ohio. The station for the type is near Ithaca, New York, as the name might indicate ; the type speci- men is on sheet No. 225037 U. S. National Herbarium ; was collected at Fall Creek, September, 1893, by K. M. Wiegand. Sheet 292227 is the same from Westmoreland County, Penn- sylvania, 1878, by P. E. Pierron, consisting of uppermost leaves and a panicle each of staminate and pistillate flowers. It is also in U. S. Herbarium in flower only, from Elyria, Lorain County, northern Ohio, as collected in flower only by A. E. Ricksecker, August 1, 1894. Excellent specimens, true to the type, are in the Herbarium of the Geological Survey of Canada as follows : sheet 34165 from Sandwich, Ontario, by John Macoun, July, 1901 ; also another from Bellville, Ontario, by the same as early as 1867, this in male flower only. All the so-called Rhus glabra from the geographic region so indicated, differs from the southern R. glabra and the New England R. -pyramidata in points quite sufficient to establish it in the rank of at least a strong subspecies. 5. RHUS ASHEI (Small). Rhus Caroliniana Ashe, Bot. Gaz. 20: 548, 1895, not of Mil- ler, Diet. 1768. Schmaltzia Ashei Small, Fl. 729. Shrub erect but low, only 3-5 dm. high ; leaflets 13-17, oval to oblong lanceolate, 5-7 cm. long, acute, not acuminate, sessile, rather coarsely subserrate-dentate, the teeth about 10 on each side, pale beneath but not glaucous : panicle of ovoid outline, large for the plant, 10-15 cm- l°ng- I SO GREENE In old fields and low woods of middle North Carolina, col- lected by Ashe, who correctly indicated it as a good new species but under a name long preoccupied. 6. RHUS PYRAMIDATA, sp. nov. Both the shrub and its foliage smaller than in R. glabra, the mature leaves firmer, almost subcoriaceous, equally white with bloom beneath, the whole leaf 3 dm. long or less; leaflets 17- 21, sessile, oblong-lanceolate, acuminate, lightly serrate, the serratures 12-16 on each side: fruiting panicle large, notably compound, the primary branches being again widely branched, the whole subpyramidal, 8-12 cm. wide toward the base and only 12-18 cm. high ; drupelets very numerous, smaller than in southern allies, 3 mm. wide, suborbicular inclining to ovate. This definition I trust may prove to include a large part of what has been called Rhus glabra in northern New York, New England and adjacent Canada. That which I wish to cite as the type specimen is on sheet 312308 of the National Her- barium, and was collected near Lake Waccabuc, Westchester County, New York, by Mr. C. L. Pollard, August 12, 1894. The locality lies easily within the range of Colden's field studies made in the middle of the eighteenth century or earlier. It might therefore be guessed that R. -pyramidata also entered into, and formed a part, bibliographically speaking, of Linnaeus' aggregate R. glabra. But this cannot be established as a fact ; nor would it alter the situation in the least if it could be ; for Colden did not describe the shrub, and his work is of later date than that of Dillenius, to which we are obliged to resort for any described and definable thing that may bear the appellation Rims glabra Linn. The Rhus glabrum of Philip Miller, which he said was from New England, and which he reported as cultivated in his time under the name of New England Sumach, cannot have been the present species ; for he attributes to that " downy " branches, as I have already remarked under R. glabra. There is presumptive evidence in the herbaria of the existence in southern New England of at least two more species, the diag- noses of which cannot be safely made for want of fruiting pani- A STUDY OF RHUS GLABRA 1 8 1 cles. One of these I have seen only in the herbarium of the Field Museum, sheets 13682 and 185 10. Both specimens were col- lected and distributed by the late D. C. Eaton, somewhere near New Haven; no date. Another is from South Hadley, Mass., 1887 ; the collector's name illegible. This is on sheet 275445 of U. S. National Herbarium. By evident marks of foliage and detached flowering panicle this is certainly distinct from all others known, and nearest R. ithacensis, unless the panicle be pyramidal. 7. RHUS CAROLINIANA Miller. RJius glabra, -panicula sfiarsa coccinea, Catesby, Carol. App. 4, t. 4. Rhus glabra Linn. Sp. PI. 2 ed. 380 (1762) in part onlv, and as to the shrub of Catesby. Rhus Caroliniana Mill. Diet. ed. 1768. Rhus elegans Ait. Hort. Kew. 1 : 365. 1789. Shrub 2-3 m. high: leaves large, but of only 13-17 leaflets, these not closely approximate but large, commonly 8-1 1 cm. long, 2-3 cm. wide, subsessile, acute rather than acuminate, strongly serrate, the serratures about 9 on a side, upper face deep green, lower glaucous : fruiting panicle large and not com- pact, exactly pyramidal, 2 dm. long or more, 1.5 dm. wide at base ; drupelets uncommonly small, bright scarlet rather than dark-red in maturity. A South Carolinian species, collected, described and illustrated by a large folio plate, in the middle of the eighteenth century, by Catesby, who also was the medium of its introduction into English parks and gardens at the same time; from which, also, it is probably long since lost. That it is thoroughly distinct from R. glabra Catesby's description and figure demonstrate, to all who know Rhus glabra. Philip Miller also knew it to be distinct, and in the year 1768 gave it the trivial name of R. caroliniana. Again, as still grown in Kew Gardens twenty years later than the date of Miller's work, Aiton, as if ignorant of Miller's name R. caroliniana, published it again as distinct from R. glabra under a new name, R. elegans. From a highly instructive paper on some small trees observed 152 GREENE in Georgia, published by Mr. Roland M. Harper last year,1 it appears to me probable that this zealous explorer of southern fields and woods has, without knowing it, rediscovered this large scarlet-fruited Rhus of Catesby. Mr. Harper says that he found what he took for Rhus] glabra "in a cane-brake on the bank of the Coosa River, in Floyd County, about twelve miles below Rome, Georgia, a veritable little grove of this species, in which many of the specimens were as much as seven inches in diameter and thirty feet tall, with the lowest branches higher up than I could reach." Mr. Harper describes the drupelets of this tree as " bright scarlet," just the color men- tioned by Catesby more than a century ago, as being one among several marks by which R. caroliniana was to be distinguished readily from the then well known R. glabra, the fruits of which are unvaryingly of a dark crimson when mature. 8. RHUS ATROVIRENS, sp. nov. Stout upright shrub, the young branches and lower face of foliage not very glaucous : leaves about 3 dm. long, with unusually stout petiole and rachis, the whole more firm and ascending than in allied species : leaflets about 23 and closely approximate, subcoriaceous, of a dark green above, pale but not white beneath, of only middle size, 5-7.5 cm. long, nar- rowly oblong-lanceolate, subsessile by an obtuse base, the apex subulate-linear, entire, the serratures of the margin, though obscure very numerous, 16-22 on each side : panicle of fruit narrowly pyramidal, 1.5 dm. long, compact; drupelets larger, than in the last, quite rotund, 4 mm. wide, deep crimson as in most species. Mountain region of northern Alabama ; type in the National Museum No. 19814, from near Gadsden, 1888, by Gerald Mc- Carthy. Distinguished from one and all the foregoing by its narrow and crowded dark green and rather rigid leaflets. 9. RHUS PULCHELLA, sp. nov. Branches not stout, angular, glaucous, minutely lenticellate : leaves not large, about 2 dm. long, rather long-petioled, of a 1 Torreya, 5 : 163. A STUDY OF RHUS GLABRA 1 83 somewhat glaucescent green above, very glaucous beneath ; leaflets 13-17, small, sessile, drooping on the rachis rather than spreading away from it on the same plane, oblong-lanceolate, 5-6 cm. long, slenderly acuminate and somewhat irregularly and coarsely serrate-toothed below the acumination, as well as more lightly and evenly serrate in the middle : panicle pyram- idal, small, about 8 cm. long, slender-peduncled, somewhat recurved or drooping. Known only from Yellow River, near McGuire's Mill, Guinnett County, Georgia, July 11, 1893, John K. Small; type in National Museum, sheet No. 19816. A small and very graceful species, recalling some of the far-southwestern forms found in Arizona. 10. RHUS LUDOVICIANA, sp. nov. Shrub with quite slender branches, the foliage not large ascending, glabrous except as to the hairy line of the rachis, about 2.5 dm. long; leaflets 11-15, opposite, of thin texture even in full maturity, dull green above, moderately glaucous beneath, 5-8 cm. long, attenuate, acute rather than acuminate, evenly serrate, the serratures 12-16 on each margin: panicle small, pyramidal, 8 cm. long, 4 cm. broad toward the base ; drupelets obliquely orbicular, of a dark red-purple and not strongly pubescent. The type specimen is in my own herbarium, from along the seaboard in southwestern Louisiana, at Cotes Blanches, October 10, 1884, by A. B. Langlois. A strongly-marked, probably small species, said to form low thickets in a peculiar maritime region that is still almost unknown botanically. If the Rhus angustifolia Bauhin, believed to have come from the coast of Brazil, was derived from some North American coast by that voyager of nearly or quite three centuries ago, it would be easy to fancy that the specimen in Burser's herba- rium, which became Bauhin's type, was from some shore of the Gulf of Mexico, and even may have been identical with what is here described as R. ludoviciana, and which is the only known maritime ally of R. glabra. And that which may elevate this Proc. Wash. Acad. Sci., February, 1907. 184 GREENE fancy almost or quite to the rank of a probability is the at least highly interesting coincidence that my type specimens of R. ludoviciana bear the only leaves and leaflets known to me that answer to Bauhin's description of those of Burser's specimen. He gave the number of the leaflets, their form and dimensions, the serrated character of their margin, and the narrowly atten- uate apex, not omitting mention of the darker green upper and paler lower faces of the leaflets. This, as I have said before under R. glabra, is the earliest element, historically speaking, that enters into Linnaeus' aggre- gate ; and had the latter described his Rhus species as carefully as Bauhin had described his a hundred and thirty years before him, the task of the twentieth century botanist at this juncture would have been much less difficult. 11. RHUS ARBUSCULA, sp. nov. Shrub low, tree-like in form though commonly less than 1 m. high : branches of the season glabrous, glaucous, obscurely angled, not very stout, but foliage large and ample ; largest leaves 3 dm. long, of 11 to 13 rather remote leaflets, these lance-oblong, 7 to 9 cm. long, often subfalcate, notably inequi- lateral at base, never quite sessile, the petiolule definite though very short, upper face of leaflets light or deep-green, the lower very glaucous ; serratures moderately salient, 10 to 15 on each margin, the apex abruptly and sharply acuminate : panicle pyramidal, very small for the foliage, usually but 7 to 9 cm. long ; drupelets of the smallest. Near Culver, Marshall County, Indiana ; collected August 18, 1906, by Mr. H. Walton Clark, of the United States Bureau of Fisheries. The type locality, and thus far the only known station, is a barren hill above the eastern shore of Lost Lake, near Culver, Indiana. The specimens at hand are two, both of them excel- lent, but evidently not from the same bush, and, as I suspect, from somewhat different exposures. One of them has a maturer foliage beginning to redden for the autumn ; and the branch, as well as the rachis of the leaves in this all show much bloom. A STUDY OF RHUS GLABRA 1 85 This I designate as the type specimen. The other differs only in having foliage of a clear and vivid green, and the stem shows but little bloom. Both specimens have been presented to, and will be preserved in, the U. S. National Herbarium. 12. RHUS PETIOLATA, sp. nov. Branches not stout, glabrous, glaucous, striate, roughened also by small and very protuberant lenticels : leaves ample, not long, though long-petioled : leaflets about 13, large, 8-10 cm. long, oblong-lanceolate and often subfalcate, distinctly petiolu- late, the base obviously inequilateral, apex sharply acuminate, the sides sharply but unevenly serrate, the serratures 13 to 15, upper face of leaflets of a rich deep green, the lower very glaucous : panicle small for the foliage, pyramidal, 10 cm. high, compact, the branches thinly and rather stiffly hirtellous ; drupe- lets rather large. Prairie region of the interior of Minnesota, the type from near Spicer, Minn., August, 1892, W. D. Frost, Herb. Field Mus. sheet No. 140259. Well marked by the large definitely petiolulate leaflets. 13. RHUS VALIDA, sp. nov. Branches very stout and robust, upright, at the end of the first season no longer glaucous but light brown, between cin- namon and chestnut-color, striate, copiously lenticellate : leaves not large in proportion, less than 3 dm. long ; leaflets about 15, approximate, short-petiolulate, oblong-lanceolate, 6-10 cm. long, with about 11 serratures on each margin and a short tri- angular-subulate point, texture subcoriaceous, upper face dull deep green and transverse-rugose, lower fairly glaucous but not white: panicle rather oblong-pyramidal, large, 12-14 cm* high, its branches thinly tomentulose-pubescent : drupelets many, large, little compressed, rather thinly plushy. Even in the herbarium specimens this impresses one as some- thing wholly apart from any and all eastern and southern shrubs that have been called R. glabra. The very stout stri- ated, lenticellate and upright branches, with smallish foliage 1 86 GREENE evidently more ascending than is usual in the genus, and the large rather narrow panicle — all these marks indicate a species, and one possibly somewhat local about Lake Michigan. The type specimens, all in Herbarium Field Museum, are from Hinsdale, a suburb of Chicago, and were collected October 12, 1902, by Ernest C. Smith, his distribution No. 577. I also refer here without hesitation Mr. O. E. Lansing's No. nil, as in Herbarium Field Museum, from West Pullman, 111., Septem- ber 8, 1900. Later than all these are specimens sent me late in August, 1906, from near Nashotah, Wisconsin, by Dr. H. V. Ogden of Milwaukee. These came to hand after the above diag- nosis of J?, valida had been finished, and the type specimens returned to the Field Museum. But they answer perfectly to my description of the species in every particular, and therefore only further confirm it while extending its range. 14. RHUS LONGULA, sp. nov. Stem and branches not known : leaves about 3 dm. long, with long stout ascending petiole, and 13 or 15 approximate leaflets, these 7-9 cm. long, sessile by a rounded base, the apical acumi- nation short though slenderly attenuate, the margins lightly and almost subcrenately serrate with about n or 12 serratures, tex- ture firm, hardly subcoriaceous, color dark dull-green above, whitish-glaucous beneath : fruiting panicle narrowly oblong and greatly elongated, 18 cm. long, hardly 5 cm. wide at the widest part, the short branches hirtellous-tomentulose ; drupelets of middle size and numerous. Bluffs of the Mississippi River far northward ; the special station for the type somewhere near Stockton, Minnesota ; the type specimen in U. S. Herbarium, No. 19813, collected by Mr. John M. Holzinger, August 23, 1888. Also on sheet 19811 is aflowering specimen by the same collector, of "May, 1889," which appears to be the same specifically. The station for this is not named. That R. longula, away at the western North should flower in May is noteworthy ; for its ally, R. glabra, so far southward as the valley of the Potomac does not begin to flower until July. A STUDY OF RHUS GLABRA 1 87 The eastern analogue, R. ithaccnsis, in Pennsylvania, does not come into flower before the end of July or early August. These segregates of R. glabra from the northwest, by their almost vernal flowering, reassert for themselves a more distant relationship to the eastern types than that which we should infer from their visible characters alone. 15. RHUS SANDBERGII, sp. nov. Rhus glabra var. sandbergii, Vasey & Holzinger in Herbarium Field Museum. Very dwarf, flowering and fruiting freely at 1.5-2 dm. high ; branches of the season 4-5 cm. long, angular, rusty-tomentulose and with also a few hirsute hairs, older branches glabrate : leaves small, barely 1.5 dm. long, the slender rachis pubescent on all sides; leaflets 11-13, sessile, oblong-lanceolate, 4-6 cm. long, appressed-serrate, the serratures 15-17 on each margin, apex subulate-acuminate, both faces nearly or quite glabrous, the upper deep green, the lower glaucous : panicle very small, seldom exceeding 5 cm. long, subpyramidal, its branches densely and subtomentosely hirsute : drupelets of the ordinary size and color. Said to grow in crevices of rocks, near the head of Lake Superior at Thompson, Minnesota, where it was collected in flower in July, and in fruit in August, 1891, by J. H. Sandberg, who afterwards distributed it under numbers 401 and 921. His locality for it is the only one known. I would indicate as the type specimen the fruiting one on sheet 19898 of the National Herbarium. Happily Mr. Sandberg, unlike most collectors of Rhus specimens, gathered this in both flower and fruit. Prof. John M. Holzinger of the Normal School at Winona, Minnesota, would have proposed this species as new, in his paper published in the Minnesota Botanical Studies, part 8, in 1896, but was deterred by the opinion of some authority who would have reduced R. typhina and R. glabra to one species, with this as a connecting link between them. I 88 GREENE 16. RHUS BOREALIS, sp. nov. Shrub evidently large but not stout, at least as to the branches, these smooth, glabrous, glaucous : leaves ample as to breadth, but not greatly elongated, 3 dm. long, the usual hairy line of the rachis quite hirsute, but other parts of the rachis, and also the midvein of the leaflets on both faces showing a few pilose hairs ; leaflets 13-17, subsessile, broad and approximate, oblong- lanceolate, 8-1 1 cm. long, subulate-acuminate, coarsely and closely subcrenate-serrate, the serratures about 14 on a side, texture of leaflet uncommonly thin, upper face of a light but rather lurid green, the lower glaucous almost to whiteness : panicle not large, 11 cm. long in fruit, narrow-pyramidal, dis- tinctly pedunculate, the peduncle and branches of panicle hir- sute, the hairiness more or less distinctly retrorse : drupelets larger than the average and of a lighter color, being bright crimson. Central Michigan near Alma, on dry ridges, collected Au- gust 12, 1895, by Charles A. Davis, the type specimen in the Herbarium of the Field Museum, Chicago. A fine species, perhaps common enough in central Michigan, and probably beyond the boundaries of the State southward, a region in which little or no effective collecting has been done in late years. But there is a poor flowering specimen, or fragment, in the National Herbarium which, by the one leaf it bears, I can refer here. This appears to have been sent by Mr. Beale, in 1899 ; but there is nothing to indicate who collected it, or where. Although pubes- cent, this bears no relation to R. hirta. 17. RHUS MEDIA, sp. nov. Branches rather sharply angular in maturity and sparsely dotted with small lenticels : leaves large but not elongated, only 2 dm. long, rachis not stout, whitish with bloom, glabrous except as to a tomentulose line ; leaflets about 13, large, sessile, oblong or subfalcate-oblong, broadly and abruptly pointed rather than acuminate, appressed-serrate, the serratures 13-15 on a side, the whole leaflet of firm texture and about 8 cm. long, 2-2.5 cm. wide, of a dull lightish green above, quite glaucous beneath : A STUDY OF RHUS GLABRA 1 89 fruiting panicle rather lax, slender-peduncled and as if some- what drooping but of pyramidal outline, its branches rather finely pubescent ; drupelets of middle size, notably oblique, acutish. Inhabits the region of scattered woodlands and small prairies in southern Michigan and northern Indiana and Illinois, if I rightly refer to it rather numerous specimens, collected in various places, all in young leaf and flower only. Such are in the her- bariafrom Warrenville, 111., by L. M. Umbach, July 2, 1895, and by Charles C. Deam at Bluffton, Indiana, 1897 ; but the type sheet, No. 1 24146 of the Field Museum, a perfect fruiting speci- men, is from Jackson County, Michigan, by S. H. and D. R. Camp, September 19, 1898. Sheet 6072 of the same herbarium, from Stark County, Illinois, may or may not be the same. Its detached fruiting panicle may well belong here, but the one leaf shown is attached to a flowering branch, and therefore im- mature. 18. RHUS CISMONTANA, sp. nov. Shrub doubtless low, all its parts reduced in size and rather slender as to branches and leaf-rachis, all these pale and glaucous: leaves 1.5-2 dm. long, ascending; leaflets 11-13, not crowded, of a pallid green above but only glaucescent beneath, mostly oblong and abruptly acuminate, 4-6 cm. long, only subsessile, or some of the more basal leaflets definitely petiolulate, sharply and rather closely serrate, the serratures 10-12 on each side, even the most mature state of foliage not subcoriaceous, though firm : fruiting panicle about 9 cm. high, pyramidal but narrowly so and compact ; outline of drupelets slightly inclining to ovate, being a trifle longer than broad, not depressed but rather acutish at summit. Open hills of the more westerly parts of Nebraska and Kansas, as well as probably in adjacent Colorado, if not Wyoming. The type specimens are in U. S. Herbarium No. 210241, collected by Mr. Rydberg in Thomas County, Nebraska, 1883 ; and Mr. J. B. Norton's so-called R. glabra from Riley County, Kansas, collected in 1895, appears to be quite the same; probably even Mr. Clements' specimens from northeastern Nebraska, 1893, I9O GREENE belong here, for, while in these the foliage is larger, the leaflets seem to have all the marks of R. cismontana, even to the peti- olules, these being very evident. 19. RHUS SAMBUCINA, sp. nov. Stem and branches unknown : leaves of few leaflets, the whole leaf, including the rather long petiole, little more than 2 dm. long, the leaflets 11 or 13, approximate, large, 7-10 cm. long, oblong-lanceolate, acutish at base and subpetiolulate, the apical acumination rather abrupt and short, the sides with 11 or 12 quite large and sharp serratures, the texture of mature foliage not known, color of upper face a pale glaucescent green, of the lower only paler, with nothing of the white bloom of real R. glabra: panicle not pyramidal even in flower, but rather oval, or at most oval-subpyramidal, in fruit oval, decidedly lax, the branches villous-pubescent ; drupelets of middle size. Singular species, with broad short leaves made up of few and much serrated leaflets, all pale green on both faces. The locality of this is remote and but little known. The type specimens are in Herbarium Field Museum, sheet 140404, and are from near Piedmont, South Dakota, by Alice Pratt, June and August, 1895. Unfortunately only the young foliage is present; the one fruiting panicle was preserved only as detached from the branch ; yet this matches perfectly, in its peculiar branching and laxity, the flowering panicles. In the same herbarium, sheet 123606, are flowering speci- mens of what seems to be the same, from southern Iowa, Decatur County, T. J. Fitzpatrick, June 13, 1896. 20. RHUS NITENS, sp. nov. Shrub stoutish, perhaps low, young branches and also petioles and lower face of foliage merely glaucescent : leaves short and short-petioled, the whole leaf barely 2 dm. long, the petiole and rachis stout, ascending; leaflets 13-17, closely approximate, seldom opposite, lance-oblong, 4.5-6.5 cm. long, subcoriaceous, sessile by an obtuse base, the apex cuspidately acute rather than acuminate, evenly but not deeply serrate, the serratures 10-12 A STUDY OF RHUS GLABRA I9I on a side, upper face of a lightish green but somewhat polished, the lower only pale, not whitened : fruiting panicle small, only about 8 cm. high, definitely pyramidal, its branches short, sparsely hirtellous : drupelets immature but perhaps full grown, orbicular, or a little broader than high. At 6000 feet in the mountains near Provo, Utah, July 10, 1894, as collected by Mr. Marcus E. Jones, his No. 5612 as in the National Herbarium. This differs from all other far-western species in that its foliage is almost as highly polished as that of R. copallina. 21. RHUS TESSELLATA, sp. nov. Shrub low, copiously and densely leafy, the leaves rigidly ascending, about 2.5 dm. long, the pinnae approximate; leaflets about 15, lance-oblong, 5-7 cm. long, not quite sessile, cuspi- dately acuminate, evenly and quite sharply serrate, the serra- tures 13-17 on a side, the texture subcoriaceous even at flowering time, upper face very smooth and somewhat shining, in general dark green, showing very prominently the fine whitish midvein and veinlets, but some intervals between veinlets wholly of a light green, exhibiting the whole surface as notably checkered, lower face merely pale and glaucescent, not glaucous : panicle small for the foliage ; fruit not seen. Foothills of the Rocky Mountains in northern Colorado, at alti- tudes of 6000 to 7000 feet; type specimen in U. S. Herbarium No. 257466, collected by J. H. Cowen, July 20, 1895 ; no spe- cial locality mentioned. The species by leaf characters alone is a very good one, even if the checkering of dark and light green be but accidental or occasional. The species here defined may or may not include all the so-called R. glabra of eastern Colorado mountains. 22. RHUS MACROTHYRSA Goodding. Rhus macrothyrsa Good. Bot. Gaz. 37 : 56. 1904. Shrub 1.5-2.5 m. high, glabrous except as to vigorous young growing shoots, these at base ferruginous-tomentose : leaves 2-2.5 dm. long; leaflets 9-15, green above, not glaucous be- neath, oblong-lanceolate, sessile, acuminate, sharply serrate : I92 GREENE fruiting panicle open, large, oblong-fusiform, 15-25 cm. long, recurved, its branches coarsely pubescent : drupelets little com- pressed, 3 mm. wide. Calientes, Nevada, 1902, L. N. Goodding. No specimens seen by the writer, but by the description the species must be distinct enough, and probably local in southern Nevada. 23. RHUS ARGUTA, sp. nov. Shrub said to be 1-3 m. high, the branches stoutish, smooth, glabrous, glaucous even in full maturity ; leaves notably ascend- ing rather than spreading, 3 dm. long, the petiole uncommonly elongated and, like the rachis, very glaucous; leaflets 17 or 19, narrowly oblong-linear or subfalcate, 6-8 cm. long, sessile by an acutish base, closely, sharply and saliently serrate, the ser- ratures 15 or 16 on a side, the acumination long and narrow, upper face deep green but dull, the transverse veins conspicu- ously paler, lower face very glaucous : panicle not large, 10-12 cm. high, pyramidal, its branches hirsutulous ; drupelets of the largest. Species of the Pacific slope, apparently common in the Columbia River region, at least eastward ; very possibly an aggregate, resolvable into several ; but the type of the above diagnosis is from Rhea Creek, Morrow County, Oregon, and was collected by J. B. Leiberg, September 11, 1894, his No. 893 as in U. S. Herbarium. The following, all from western Washington, are more or less true to this type : sheet 93075 in Herbarium Field Museum, from near Spokane, in flower only ; sheet 93076 of the same, from the same region with lax pyram- idal panicle very much larger, leaflets larger, greener on both faces and by no means sharply serrate ; A. D. E. Elmer, Wawawai, 1897 ; Frank Kreager, Spokane County, 1902 ; Sandberg & Leiberg, Rock Island, 1893, and Robert Horner, Waitsburg, 1897, these last all as in U. S. Herbarium, likewise from Idaho, A. A. Heller, Nez Perces County, 1896, his No. 3421. This is quite true to the type as to foliage, but in flower only; a fruiting specimen, from Salmon River, Vernon Bailey, 1895, with leaflets not so typical. A STUDY OF RHUS GLABRA 193 Among all these there is nothing of Torrey's Rhus glabra^ var. occidentals. Nearly all that I have seen of Pacific coast material which matches that of the Wilkes Expedition, comes not from Oregon or Washington, but from British Columbia. 24. RHUS APRICA, sp. nov. Dimensions of shrub, and characters of branches unknown : leaves as a whole remarkably broad and short, the leaflets being few and approximate but large, subcoriaceous, deep green above, light green beneath, but without bloom ; leaflets about 15, oblong, 6-8 cm. long, obtuse at base and sessile, at apex only cuspidately acute, not acuminate, very evenly and quite distinctly though not sharply serrate, the serratures 10 or n on each margin : panicle pyramidal, small, about 8 cm. high, its branches only sparingly and obscurely villous-pubescent ; drupe- lets rather large. Very well marked by its few and large leaflets green on both faces; but known only as collected by M. W. Gorman, on Camas Creek in the Washington State Forest Reserve, August 20, 1897. It is said to occupy dry open grassy slopes. The type specimen is in U. S. Herbarium. Its label bears Mr. Gorman's collection number 632. 25. RHUS OCCIDENT ALIS (Torrey). Rhus glabra occidentalis Torr. in Bot. Wilkes' Exp. 257. 1874. Only flowers and young foliage known : leaflets (in what should be the type specimen, U. S. Herbarium sheet No. 19819) 11-13, oblong-lanceolate, sessile, notably acuminate, beneath only glaucescent ; the panicle small and very slender peduncled ; even the branch slender, but quite glaucous. The label bears, in the handwriting of Asa Gray, the legend, "Okanogan, Wash. Territory." The Okanogan region lies partly in Washington and partly in British Columbia, and all the more recent specimens seen by the writer which match the type are from the Canadian part of the region. Sheet 4471 of the Canadian Survey Herbarium, Arrow 194 GREENE Head Lake, near Lake Okanogan, is every way true to the type, except that the leaflets are less numerous ; nine in most of the leaves and none with a greater number, a few having seven only. In the same herbarium 4473, from Spence's Bridge, in the same general region, has mostly 13 leaflets. The like is true in the case of number 63749, collected at Cascade, B. C, by Mr. J. M. Macoun in 1902. But all these specimens are in one and the same unsatisfactory condition of early flowering, with foliage, of course, not fully grown. They indicate, how- ever, a northerly species, from which the two Washington spe- cies herein characterized are sufficiently distinct. Not, however, until mature foliage and fruiting panicles of it shall be brought to light can R. occidentalis be properly described. 26. RHUS ALBIDA, sp. nov. Probably low, the branches not robust, very light-colored and, with the rachis and lower face of leaves, much whitened with bloom, even the upper face of foliage of a pale color and glaucescent : leaves 1.5-2.5 dm. long; leaflets about 13, not crowded, not deflected but spreading, subsessile, 4-6 cm. long, oval to oblong-lanceolate, abruptly acute or short-acuminate, saliently serrate, the serratures 10-14 on each side : fruiting panicle about 1 dm. high and quite broadly pyramidal, its branches only very delicately but rather densely velvety : drupe- lets much compressed and acutish. As far as known this very beautiful Rhus is local on the San Francisco Mountain not far from Flagstaff in northern Arizona. The type specimen, sheet No. 410696 of the National Her- barium, was collected there, at an altitude of between 6000 and 7000 feet, August 18, 1901, by J. B. Leiberg, his distribution No. 587 1. A perfect male flowering specimen is in my own herbarium, as collected by myself at the same station, July 13, 1889. Again, National Herbarium sheet 334404 holds a flower- ing branch from the same locality by D. T. MacDougal, his dis- tribution No. 309, July 18, 1898. This, too, from an altitude of about 7000 feet. The late date of its flowering, as an ally of Rhus glabra in the generally torrid climate of Arizona, indi- cates the subalpine character of its habitat. A STUDY OF RHUS GLABRA 1 95 27. RHUS ELEGANTULA, sp. nov. Branches slender, glabrous, of a distinctly pinkish brown underneath a coat of bloom: leaves small, 1.2- 1.8 dm. long, the slender rachis quite white with bloom, its villous line very marked; leaflets 11-15, loosely arranged, spreading or slightly deflected, distinctly petiolulate, 4-6 cm. long, narrowly subfal- cate-lanceolate, at least the long and slender acumination falcate, sometimes the whole leaflet, the serratures, about 8 on a side, more or less sharply prominent, the texture rather firm, color of upper face pale bluish-green, the lower whitish with bloom : fruiting panicle large in proportion to the foliage, commonly more than 1 dm. high, pyramidal but narrowly so, its branches thinly villous with ascending or spreading hairs : drupelets small, arranged upon simple racemose branches of the panicle, compressed, acutish. Mountains of extreme southern Arizona along the Mexican boundary, the typical specimens from about Fort Apache, by Edward Palmer, June, 1890 ; these on sheet 19808 of the National Herbarium ; others distributed by Dr. Palmer under his No. 585. Probably the same as a specimen from the Santa Catalina Mountains, September, 1896 by J. W. Tourney, U. S. Herbarium sheet 441724. Lastly rather larger specimens, but otherwise true to the character, have come in this season from the Huachuca Mountains, sent by Mr. J. C. Blumer, who col- lected them late in August, 1906. 28. RHUS SORBIFOLIA, sp nov. Shrub apparently low and not stout, the young branches and lower face of foliage not whitened, hardly paler than glauces- cent : leaves small, only 1-2 dm. long, spreading away from the stem divaricately, or even a trifle deflected, the petiole and rachis rather slender; leaflets few, only 9 or 11 and loosely arranged, dull deep green above, glaucescent beneath, of small size, 2.5-6 cm. long, oval to oblong-lanceolate, sessile by an abruptly acutish base, at apex subulate pointed rather than acuminate, rather remotely and sharply serrate, the serratures only 7-9 on each margin : panicle of staminate flowers pyram- I96 GREENE idal, 12 cm. long : sepals triangular, acute; petals twice as long, oblong, obtuse, the anthers equaling them. Type from mountains west of Las Vegas, New Mexico, G. R. Vasey, 1881 ; U. S. Herbarium No. 195 10. Species with most characteristic habit and foliage. 29. RHUS ASPLENIFOLIA, sp. nov. Shrub evidently dwarf or at least low, the leafy branches short, slender, tortuous, glabrous, glaucous : leaves small, about 1.5 dm. long, the rachis slender, deeply and narrowly furrowed and the hairy line obvious ; leaflets only 7-9, pale green above, moderately glaucous beneath, oblong-lanceolate to lanceolate, 3.5-5.5 cm. long; subsessile, acuminate, very irreg- ularly and somewhat incisely serrate, even coarsely so, the serratures now and then so deep and large as to amount to lobes rather than serratures : only a staminate panicle seen, this narrowly pyramidal, 5 cm. long. Type from Wolf Creek, Wyoming, July 12, 1896, A. Nelson, distributed to U. S. Herbarium, under No. 2303, mounted on U. S. Herbarium sheet 285144. Manifestly intermediate be- tween the Nebraskan R. cismontana and the characteristic species of Arizona ; the foliage peculiar. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 197-403. February 13, 1907. ASPECTS OF KINETIC EVOLUTION. By O. F. Cook. The kinetic theory of evolution finds in the facts of organic development indications that the characters of species change spontaneously, or without environmental causation. Evolution- ary progress is further conceived as accomplished through the union of the normally diverse individual members of species into a coherent network of interbreeding lines of descent, rather than by the isolation of variant individuals or by the selective restric- tion of descent to individuals possessing particular characters. Former theories have undertaken to explain the method of evolution by reference to the dendritic figure of descent as shown in the ever-branching relationships of species, genera and fami- lies. The kinetic interpretation of the evolutionary process is based on what may be called the intraspecific figure of descent, the relationship of organisms inside the species, which is reticu- lar or net-like, and not tree-like. Theories based on the dendritic conception of descent may also be described as differential ; that is, they have given atten- tion chiefly to the problems of distinction and separation of organic groups. The kinetic theory is integral or synthetic, and conceives the evolutionary process as conducted by the accumulation and combination of the variations which appear among the members of the species. These simple distinctions are fundamental, and will neces- sitate an extensive readjustment of methods of thought and investigation in the field of evolution. I98 COOK Various aspects of the kinetic theory have been presented in earlier essays, of which the present chapters are a continuation. Indeed, it is likely to become apparent to the reader that they have been written at different times and that they often lack unity and consistency. The same ground has in some cases been traversed repeatedly and in different directions, but the frequent restatement of the same distinctions appears to be necessary in the development of so large and complicated a subject. My thanks are due Mr. Walter T. Swingle for much helpful interest and criticism. 1. KINETIC EVOLUTION AND THE FITNESS PROBLEM. The theory that evolution is caused by natural selection and the survival of the fittest is now commonly admitted to be inad- equate, but our studies tend, as usual, to follow the beaten paths of thought, and adjust themselves only with reluctance to new interpretations. The point at which the selection theory becomes obviously deficient is that it does not account for the fitness to which the evolutionary progress is ascribed. This has given rise to the attempt in recent years to penetrate farther into what has been called " the problem of fitness," on the natural assump- tion that more light could certainly be reached in the quarter whence came the first suggestions of evolutionary illumination. Nevertheless, those who have followed closely on the route of natural selection have not yet come through into regions of clear vision. Fitness is the primary idea of the doctrine of evolution by selection. Fitness affords the cogs, as it were, by which evolu- tion is supposed to be worked by the environment. Even if we were to admit, for the argument, that evolutionary motion could be caused by selection towards greater fitness, the evolutionary factory would still lack the very important facility for providing these cogs of fitness by which the environment could gain a hold upon the species and roll them along. Some selective evolutionists have assumed that environment could form the cogs by impressing itself upon the species, and others that the species could, as it were, wrinkle itself in response to external stimuli, and thus give the environment a selective impingement. ASPECTS OF KINETIC EVOLUTION 1 99 These suggestions have not been able to retain the full con- fidence of biologists for the selective theory, as witness the recent remarkable diversions towards Mendelism and muta- tionism. The prompt acceptance of these doctrines by so many students of evolution is not justified by any indication of general pertinence for the facts on which they are based. They met with immediate welcome because they afforded a suggestion, at least, of methods by which new characters or character-com- binations could be produced. They promised, in other words, the long-needed supplement of the selective theory, the cogs which selection might turn. The kinetic theory recognizes that evolution does not depend upon selection nor upon the environment, and still less upon mutation and Mendelism. The evolutionary causes are in the species, not in the environments. They are resident, moreover, in species as constituted in nature, and are exemplified only abnormally in the phenomena which become prominent in the close-bred domesticated plants to which the studies of Mendel and De Vries were mostly directed. TWO TYPES OF ORGANIC FITNESS. The current belief in the environmental causation of evolution is largely due to the confusion of two different kinds of organic fitness, (i) The general fitness of the species for the environ- ments in which they exist ; and (2) the special fitness or power of adjustment of the individual organisms to particular condi- tions which they may encounter. An interesting example of the extent to which these two distinct phenomena have been confused may be found in so well known a work of reference as the Standard Dictionary. Adaptation is defined as "an ad- vantageous conformation of an organism to changes in its envi- ronments," but the quotation given to illustrate the use of the word in this sense alludes to the " special adaptations " of deep- sea organisms. The definition applies to the second type, fit- ness by individual adjustment, while the example refers only to the first type, the general fitness of the species, genus or family as a whole. No method has been suggested whereby either type of fitness Proc. Wash. Acad. Sci., December, 1906. 200 COOK can be caused by the environment, but the fact that individual adjustments do have definite relations to the environment, has served to sustain a belief in the environmental causation of evo- lution. All species have, of course, fitness for their environ- ments ; otherwise they would not continue to exist. They must be more fit than other species which have had access to the same environments, or they would be driven out. Neverthe- less, inside of the general environment, or place of the species in the economy of nature, there is still a very great diversity of individual experience to which each organism must adjust itself. The environment at all times determines the relation of fitness, but the characters which afford the fitness are as truly results of evolution as any other characters. It has not been shown that they are caused by the environment or that they can be inherited from it. The doctrine of environmental causation of evolution supports one assumption by another equally baseless. It takes for granted that adjustment differences between individuals of the same species are caused by the environmental differences which are met by these same adjustments. It also takes for granted that the general fitness or adaptation of the species is merely a product of the fitness of individual adjustment, whereas there are two phenomena of fitness which are quite distinct in their relations to the problem of evolutionary causes, though neither of them affords any special indication regarding the nature of such causes. The adjustment of individuals to differences of environment is a form of organic elasticity which permits lateral vibrations or displacements of characters, while the fitness of a species or genus as a whole is, obviously, an accomplished result of evolution instead of being a formative principle or cause. ADAPTIVE VERSATILITY OF ORGANISMS. To say, as has been the custom of writers on evolution, that organisms are plastic or susceptible of environmental influences, is only half of the truth. Organisms are not merely plastic, but versatile. Under different conditions they are able to grow in different ways, and often in ways which qualify them better for existence in these particular conditions, though not neces- ASPECTS OF KINETIC EVOLUTION 201 sarily so. A Guatemalan variety of the cotton plant takes on in Texas a robust, upright habit of growth very distinct from that of its Central American ancestor. It might be held that this deviation from the previous type serves a purpose in the internal economy of the plants, in enabling them to carry on more efficiently the process of vegetative development. Never- theless, it cannot be reckoned as a truly adaptive change, since it does not improve the chances of the survival of the variety in the new environment. These very large and vigorous plants are relatively infertile, and ripen their fruits much later than those which retain the normal low-growing parental form. This behavior of the cotton plant is not the exception, but accords with a general tendency of tropical plants toward excessive vegetative development when first planted in northern latitudes. The longer days and higher temperatures of our summer seasons are not utilized for earlier and larger production of fruit, but are wasted in riotous vegetative expansion often cut short by frost before a single seed has been formed. New environments may also throw plants into a condition of morphological instability* which can scarcely have any relation to adaptation, since the result is an endless diversity of abrupt variations or mutations along many different lines, including the most opposite. The hereditary coherence of the species or variety is lost, and the individuals scatter, as it were, in all direc- tions. This explosive type of variation is occasioned, obviously, by changes of environment, but it is equally obvious that one and the same change of environment cannot be directly described as having caused many diverse variations ; it need only be thought of as having occasioned an abnormal intensification of normal individual diversity. In some manner, quite unknown as yet, changes of conditions do induce changes of methods of development, but to infer that these changes are always advantageous, or that the external causes actuate the modified development of the organisms, is bad logic and worse biology. Curiously enough, it is only at one particular point that such reckless conclusions are indulged. When we find a dozen dif- ferent species of plants growing on the same square yard of soil, 202 COOK it does not occur to us to suppose that their diversities are due to the different conditions under which they have grown, for the conditions are the same. We accept without debate the fact that the plants are developing each according to the methods of its own species. It is only when we find plants of the same species following different methods of growth when under different con_ ditions that we can be betrayed into supposing that the condi- tions are producing the characters of the organisms. In reality this reasoning has no more propriety when we compare a plant or an animal with another member of its own species than when we compare it with a member of a different species. As long as the adjustments are physiological only, we do not find it necessary to marvel, but when they become appreciable from the morphological standpoint our interest is aroused. And when accommodations cause taxonomic difficulties by affecting the characters by which we have described species, some are ready to believe that environment must be responsible for evo- lution because it can be alleged to change the characters of species. To reach this conclusion the amassing of detailed knowledge of plants and animals was superfluous. It could have been based quite as logically on the fact that rain " causes " us to carry umbrellas, and to wear waterproof coats. The African variety of mankind adopts the reverse policy, but no less appropriate to the occasion. He discards all of his scanty wardrobe and gives his naked skin a coat of palm oil. The birds can not change or take off their feathers, but their own organization provides a convenient supply of oil, and an instinct to use it when needed. Plants can neither go in when it rains nor oil themselves, but many plants grow a water-shedding coat of wax or of fine hairs on the upper surfaces of their leaves. All species of plants and animals have, as already remarked, not only their general specific methods of development, but they have in addition certain ranges of adjustment to the different conditions under which they are able to exist. The environ- mental qualifications of a species are not to be represented by a single point, but by maximal and minimal boundaries, like the geographical latitudes and longitudes which may be used to indicate its position on the earth's surface. ASPECTS OF KINETIC EVOLUTION 203 It is usually possible to discover somewhere between the pro- hibitive extremes an optimum condition, or a locality where the fullest development of the species takes place. Unfavorable conditions multiply as the boundaries are approached, and development is variously impeded and restricted, but surely the ability of the organisms to accept or to avoid a measure of such restrictions and to achieve an existence in spite of them, is small warrant for concluding that the conditions afford an adequate biological explanation of the characters. Still less are we justi- fied in supposing that the unfavorable peripheral conditions are any more truly causative than the central optima. Adverse cir- cumstances, by restricting development, would seem rather to require the organism to put forth more active energies, not of development merely, but of accommodation as well. And yet it is in abnormal features arising under abnormal conditions that the evidences of environmental causation have been chiefly found. If each species wrere restricted to an absolute uniformity of conditions and materials, the doctrine of environmental causa- tion would have had at least a partial justification, whereas the versatility of organisms, instead of demonstrating environmental causation, renders it highly improbable. The individual mem- bers of species in nature are different, even under the same con- ditions ; why should we expect them to be alike under different conditions? For some species the range of environmental conditions is very broad, in others very narrow. The fitness of the latter type of species may appear to be greater than the former, in the sense of being more highly specialized. It is not, however, the extent of narrowly specialized fitness, but the extent of widely varied adjustment which generally determines the range of dis- tribution and the numerical prosperity of the species. In a general way the power of a species to accommodate itself to different environments might be held to favor evolution, because it would improve the chances of sustained numerical prosperity, which is an evolutionary advantage. It does not appear, however, that " plasticity" wrould be especially helpful in the evolution of the particular characters which might be 204 COOK modified in adjustments to the different conditions. The "plasticity" might hinder, even, as Professor Metcalf has recently pointed out, for the ability of the species to accom- modate itself promptly would render unnecessary any perma- nent progress in the direction of these particular changes.1 Of permanent effects arising from the influence of environ- ment upon adjustment changes, there would remain only the possibility that a species which had once possessed a wide range of accommodation, might lose this by long disuse, and might thus become more narrowly specialized as a result of environ- mental influence. Thus an amphibious species, if confined long enough to a strictly terrestrial habitat, might forget, as it were, how to grow in water. That experiments have not yet demonstrated such an effect does not justify a general denial of the possibility. The phe- nomenon would be no less real if it took a hundred or a thousand years to produce it than if it required only five or ten.2 But in any case the result would be negative rather than positive, involving a diminution of the powers of the species rather than an enlargement of them. There would be a loss of characters instead of an addition, and no occasion to infer that environment had aided evolution. The case would be quite analogous with the influence of environment through natural selection, which is likewise not constructive, but wholly restrictive. Much of the existing terminology of evolutionary discussion is calculated to commit us in advance to the doctrine that the adjustment is caused by the environment, whereas the fact is that the organisms are active instead of passive, and are able to put forth their own efforts toward adjustment to the varied external circumstances. It is only in a loose and figurative sense that the environment can be said to cause the adaptive adjustments. The arctic climate "causes" the Esquimaux to clothe themselves in furs, but it does not skin the fur-bearing 'Metcalf, M. M., 1906. The Influence of Plasticity of Organisms upon Evo- lution, Science, N. S. 23 : 789. 2 An additional reason for caution in denying the possibility of a loss of the power of accommodation from disuse is found in the phenomenon of " fixing the type" of a variety by selection. The normal diversity tends to disappear when only one carefully selected type of the variety is bred for several generations. ASPECTS OF KINETIC EVOLUTION 205 animals and sew their pelts together. We say, similarly, that a desert climate "causes" a plant to become more hairy, but this is as yet a mere figment of speech. We have no notion of the chain of biological events coming between the dryness and the hairs. We can appreciate the advantage of the reduced transpiration, but we do not know how the plant puts on the additional protection against the dry atmosphere. ALTERNATIVE ADJUSTMENT CHARACTERS. We shall hardly come to understand aright the relation of fitness to evolution until we accustom ourselves to thinking of these variations of accommodation or so-called " environmental reactions " as expressions of the power of the plant or animal to choose, as it were, between alternative methods of growing and of conducting the functions of existence. Organic versatility, plasticity, or whatever it may be called, does not conduce to the rapid development of specialized char- acters (adaptation), or to the multiplication of new groups (specia- tion), but it is undoubtedly of vast practical importance in the economy of species. Some species have little of this readiness of adjustment, while others are able to adopt a great variety of forms and can thus take advantage of opportunities of existence under a great diversity of natural conditions. By keeping open a larger number of alternative lines of progress, the power of accommodation very greatly increases the ability of species to solve their environmental problems. The environment is unable to prevent such groups from accumulating many kinds of varia- tions or from making trial of them, as it were, in a great variety of combinations. This affords the best of opportunities for the construction of new types with enlarged environmental resources, instead of providing merely for the differentiation of narrowly localized and specialized species. The different characters assumed by a species in accommodat- ing itself to different environments are not less characters of the species because they are shown simultaneously than if they were developed in successive epochs of evolution. The only sense in which they are not characters of the species is the nar- rowly taxonomic one in which species are treated as having 206 COOK " identity of form and structure." Characters changed when conditions change are to be reckoned as alternative characters, no less than sexual differences. Indeed, the sex determination itself sometimes appears as an incident of environmental adjust- ment.1 Alternation of generations and dimorphism afford further analogies. There is no warrant for the supposition that the evo- lutionary status of any of these kinds of characters is different from that of characters which appear in all individuals of the species. Professor Metcalf says : "A high degree of plasticity hinders evolution b}r selection, of characters similar to those acquired by plastic response to the environmental influences." This seems to imply that alternative characters which appear responsively have to be acquired over again by selection in order to become genuine results of evolution. If this were true selec- tion might indeed be impeded. Such a distinction is not illogical, but it applies only in the metaphysical systems of evolution which assume that selection causes evolution and that environ- ment causes characters. A character which can be varied readily and which thus increases the power of the species to accommodate itself to varied environments is much more valuable than one which is not capable of such adjustment, and there is no reason to suppose that selection would favor the development of a non-adjustable form of the same character. Moreover, both the character itself and its adjustability or " plasticity" are already genuine evolu- tionary results reached by the same processes as any other characters. It is only when we have allowed our meanings to slip from harmless abstractions to fictitious concretions that we explain evolution by selection and characters by plastic response to environmental influences. However unobjectionable such ex- pressions may be if used in sufficiently general, literary senses, they are dangerously misleading as the basis of physiological inferences, because they take for granted unproved and improb- able assumptions, such as the causing of characters by environ- 1 See Fink, B., 1906. Plant World, 9 : 183. ASPECTS OF KINETIC EVOLUTION 20J ment and the causing of evolution by selection, assumptions which rest in turn on the still more general and obviously erroneous assumption that species are normally uniform and stationary, whereas they are neither. It will some day be reckoned as one of the paradoxical incidents of biological history that this static theory, which is simply a relic of pre-Darwinian doctrine of special creation, should have been cherished most jealously by the ultra-materialistic school of biology. ENVIRONMENTAL ADJUSTMENT ANALOGOUS TO LOCOMOTION. The power of locomotion is a very important adaptive char- acter of organisms because it gives great freedom of choice of environment. The hippopotamus, for example, is an aquatic animal, but the brief nocturnal excursions to the grassy river- bank or to the neighboring rice farm keep the huge bulk alive. Being animals ourselves and accustomed to use our powers of locomotion to change our environments, we fail to appreciate this form of adaptation and view with much wonder the fact that organic types have other means of dealing with environ- mental problems. Unable to change their environments, they have the alterna- tive power of changing their characters and of behaving in dif- ferent ways in different environments. Some of the most striking instances of this kind are afforded by a series of plants (belonging to diverse and unrelated natural families) which can live either in water or on land, and which have two sets of char- acters appropriate to the alternative habitats. On land they have the characters of other land plants, in water the characters of other aquatics. The mystery is that they can change from the one to the other. Some have imagined that if we could find out how this change is accomplished we would have penetrated to the causes of evolutionary changes in general. The analogy between locomotion and environmental adjustment has been overlooked, along with the probability that both these methods of adjustment have been attained by the same evolutionary processes. They are finished products and not merely charac- ters in the making. The elasticity of muscular tissues is onlv one of the many 208 COOK methods by which organisms are able to place themselves in more advantageous relations to their environment, and to man- ifest a power of choice with reference to external circumstances. Even among the simplest types of organic structure this faculty is definitely in evidence. The slime-moulds (myxomycetes) pass the vegetative period of their existence in rotten wood or other decaying vegetable matter. By simple amoeboid movements the naked, softly slimy protoplasm, of which these primitive organisms consist, is able to creep out at maturity to an exposed surface before giving up its water and separating itself into dry, wind-blown spores. To better accomplish the work of dissemination many of the myxomycetes have the hereditary talent or instinct to subdivide their colony into small masses, each of which builds itself a stalk to climb upon. There is then built out from this stalk a network of threads to hold the spores so that they can be sifted out and scattered gradually by the wind, instead of falling at once to the ground. The stalk-building myxomycetes do not work, however, by any arbitrary or merely mechanical stand- ards. When the surface of the decaying log over which they have spread themselves at maturity is uneven, so that a part of them must stand in wet depressions or chinks of the bark, these have longer stems than the others. In some species only those in the wet situations will have stems, while those in exposed places will remain seated directly on the substratum. The building of the stem and the climbing up are not two dif- ferent adaptations, but are merely the two aspects of the same act of adjustment to environmental conditions. In some con- nections it may do no harm to say that the wet situation causes the long stem and causes the slime mould to climb up, but for biological purposes all such statements must mean very little until we know something of the chain of events between the wetness and the building and climbing. Still less defensible is the policy of saying that the stem is " caused" by the environ- ment while the motion is "spontaneous" in the organism. Mechanical biologists would be consistent, at least, in ascribing both acts to " stimuli." The myxomycetes have long been objects of special interest in ASPECTS OF KINETIC EVOLUTION 20O. the scientific world because they have been thought to combine the characters of animals and of plants and thus to afford a con- necting link between the two organic kingdoms. Beginning with such a primitive and undifferentiated form of life, it is easy to think of the animals as gradually specializing the power of locomo- tion, the plants the alternative powers of morphological and physiological adjustment. The animals excel in seeking their own environments, the plants in the ability to take what comes. The purpose of this rehearsal of elementary facts is merely to convey, if possible, the suggestion of an idea of organic elasticity, so to speak, of which muscular contractility and loco- motion are the extreme specializations, but which extends into all departments of organic activity, morphological as well as physiological. Some may still prefer to say that the environ- ment " causes" the adjustments to be made, but it will remain none the less true that the organisms themselves make the adjustments. Zoologists speculate on such questions as whether the eggs of Vancouver wood-peckers, if transferred to Arizona, would hatch Arizona wood-peckers, or whether the transferred individuals would gain Arizona characters in a few generations. What the wood-peckers might or might not do depends on the amount of organic elasticity which they may happen to possess, but the ex- periment is unnecessary for answering the general question, since plants show a high development of these powers of prompt adjustment to diverse conditions. It is not even necessary that the eggs be hatched in Arizona. Many plants, as already noted, can adjust themselves to such changes at any stage of their ex- istence, and are regularly accustomed to do so. They are both fish and flesh. In water they have the form, structure and func- tions of other strictly aquatic species ; on land they are equally ready to behave as terrestrial species. Needless to say, hundreds of plants have been described as new species which proved afterward to be only land, water, shade, sun, or other environmental forms of previously known species, and such unnecessary "species" continue to be de- scribed. There is no way to ascertain from a few her- barium specimens whether their differences represent the results 210 COOK of evolution as isolated groups or are merely adjustments to different conditions, any more than it could be ascertained with- out local study whether an individual bird-skin represented a regular resident, a migrant, or a still more accidental visitor. In this merely taxonomic or nomenclatorial sense the envi- ronment can be said to cause species, but such a statement has no warrant in the field of evolution. If we have undertaken to diagnose species by characters which represent merely environ- mental adjustments our only course for the future is to recognize and rectify our mistakes, and not attempt to utilize them as the basis of doctrines of environmental causes of evolution. For physiological and evolutionary purposes the species is not to be thought of in the mere systematic sense, as represented by the original specimen or even by the form in which the plant appears in what are supposed to be its normal conditions. The ■physiological and evolutionary species covers all the forms tinder zvhich the organism can maintain itself and complete its life- history, to say nothing of the definitely abnormal results shown when conditions are too adverse. Adjustment characters, as such, are not inherited, according to the usual definition of inheritance, that is, they are not necessarily repeated in each generation, but are readily recover- able when needed, even after long periods of time. The plant or animal if kept for many generations under the same envi- ronment may continue to show the same adjustment, but this may be completely changed by transfer to other conditions of growth. Thus at 4000 feet coffee has a more strict and upright habit of growth, darker, firmer foliage and larger seeds than at 2000 feet, but if seedlings from the two altitudes be exchanged they always grow into trees showing the characters appropriate to their new situations. It appears, therefore, that both kinds of fitness, the general features which adapt the species as a whole to its place in nature, and the special powers of adjustment which assure to the indi- vidual a certain latitude of environmental opportunities, are normal characters of species, quite as much as those which have no such acute relations to the environment. Unless we can resume and carry to completion the Darwinian task of ASPECTS OF KINETIC EVOLUTION 211 proving that all characters have arisen as useful adaptations, other methods and causes of evolution must be sought. To question the adequacy of selective and environmental causes is to admit at least the possibility that such theories are completely erroneous, for any causes which are adequate to produce and develop useless characters can produce, a fortiori^ useful ones. There are enough adaptations to occupy many naturalists for many life-times. They can, if they prefer, live and die without hesitating to entertain doubts of the efficiency of enviromental causation. And yet the fact will remain that the great majority of the differences between related species and between the indi- viduals of the same species have no environmental utility at all, and are quite unlikely to have had any. This is not to be as- certained by denying or affirming the theoretical utility or use- lessness of a few selected characters, but by observing whole orders and classes of organisms to learn the general proportions between differences of characters and differences of environ- mental relations, and by perceiving that the former vastly out- number the latter. The fitness which the individuals of a species of plants can attain by adjusting themselves to the special conditions is, as we have seen, a kind of stepping aside, a morphological motion, put forth by the organism itself as truly as are the coordinated muscular acts which enable the higher animals to move from place to place and thus to choose their own environ- ments. A perennial plant must arrange to tolerate whatever extremes of temperature, moisture, and exposure to sunlight its habitat may provide. Its powers of making such adjustments may be reckoned as functions of its tissues and organs in quite the same sense as locomotion and sustained high temperature are functions of the animal organism. The plant withstands a temperature range of a hundred degrees and more, but mammals and birds establish their own temperatures and keep them ad- justed to tenths of degrees. It is a regular custom for many of them to travel annually for thousands of miles to find congenial conditions. The arctic plover is said to fly every year the whole length of the continent from Greenland to Patagonia and back again.1 ' Knowlton, F. H. 1902. The Journeyings of Birds, Pop. Sci. Mon. 60 : 323. 212 COOK The power to make or maintain such adjustments, whether by changes of muscular or other tissues, may well be reckoned as a character of a species, but there is nothing to show that morphological powers of adjustment are different in any evolu- tionary respect from the others, or that they afford any warrant for the inference that evolutionary changes are due to environ- mental differences, or that they arise first as adjustments to external conditions. Any change which increases fitness has the advantage of selective encouragement, and is thus able to exert a larger influence in determining the evolutionary course of the species, so that evolution tends ever toward greater fitness, though other lines of progress are not excluded. If changes could take place only in adaptive characters, the difficulty of maintaining fitness would be greatly increased, because charac- ters would need to be useful from their very inception, whereas they have now the possibility of becoming useful at any stage of their expression. Selection begins to discriminate against a character only when it has become harmful. SELECTIVE PERFECTION OF ADAPTATIONS. It is not intended to imply that there are never any direct reactions to environmental influences or that such reactions are never of advantage to the organism. The Washingtonia palm of the deserts of Southern California has a complete covering of dead leaves over the whole length of its trunk, and secures, no doubt, a very desirable protection against the extreme heat and dryness. The retention of the leaves is made possible because the climate is dry. Palms native in humid regions usually drop their dead leaves promptly, but if not they are soon weakened by decay and fall away. Such coincidences could scarcely be avoided in any relations so complex as those of biology, but it does not appear that they are of a nature or fre- quency to give them more than a very subsidiary importance in evolution. A plant or animal that encounters adverse conditions and is not able to obtain sufficient food will remain stunted. This small size is an advantage, however, in a region where food is scarce or uncertain. Nevertheless it is those individuals of the ASPECTS OF KINETIC EVOLUTION 213 species which are naturally small, that is smaller than most of their kind, even under favorable conditions, which would be able to make this reaction most successful, since they would be less stunted, or less abnormal, than the others. Thus even the simplest cases of environmental reaction are not to be separated, for evolutionary purposes, from the phenomena of normal diver- sity among the members of the species. Selection, as far as it influences the movement of the species toward adaptation, works through this intraspecific diversity rather than through the environmental reactions. The reactions are not selected, but the individuals which happen to excel in making the reactions. Another case illustrating the same principles is that of the inconspicuous colors of the desert animals. Selection is sup- posed to have produced these inconspicuous colors because they conceal the animals, and thus give them protection against the enemies to which they would otherwise be very much exposed. The insecurity of this assumption becomes apparent as soon as we consider the equally striking fact of nature that desert plants also have the same series of dull shades of pale grayish and brownish colors. It would seem, therefore, that evolutionary inferences regarding the colors of the desert organisms will have to provide for the plants as well as for the animals, and that they must not depend wholly upon the idea of protection against predaceous foes. From the plants it is very easy to gain another clue to causes of the obscure coloration. The vegetative tissues of desert plants are usually as green as those of species native in humid regions, but in arid climates the soft, thin-walled, green cells have to be covered by thick integuments to protect them from the dry air, and from too great intensity of light and heat. The modified colors seem to be purely incidental to the modified integuments which mask the green tissues within. The thick- ened, specialized outer skins simply protect the plants against the too rapid loss of water, and enable them to withstand more severe conditions of drouth. Many other species living under exactly the same conditions of exposure are nevertheless able to retain the fresh green colors of plants of humid regions, because they have solved their transpiration problems in other ways, just 214 COOK as there are a few bright colored desert animals. The pigments which determine the color lie in the deeper layers of the skin, and are readily concealed by a thickening of the superficial layers, or by the development of darker pigments above to pro- tect the lower cells from sunlight, as in the human species. When the color is resident in an outer covering of hairs, feathers, or scales, a very direct environmental reaction takes place, for these are no longer actively living, and the strong sunlight can bleach out the colors as well while the animals are alive as after they are dead. This is true of many insects and also of the horned toad, young or recently moulted individuals showing a bright yellow which is lacking in the old. Finally, the protective coloration doctrine loses another instal- ment in the fact that in the brilliant lights of deserts no colors are very conspicuous. There is no occasion, so to speak, for the development in desert animals of the brilliant tints which may enable the members of the same species to more quickly recognize each other in the sombre depths of tropical forests. There have been, no doubt, many cases where the protective colors have been of immense advantage in the severe struggle for existence to which animals are often exposed. Selection must have had an immense influence in perfecting the marvel- lous adjustments which many species have with their environ- mental conditions. The nicety of some of . these adjustments cannot be exaggerated — it is already past credence. A little fish, common in Liberia, is so exactly the color of the water- covered sandy stream-beds over which it swims that its presence is often betrayed only by the darting shadows. A little frog living in the sandy pools of the California desert canyons has the same elaborately speckled browns and grays, and likewise becomes invisible, except for the shadows. A slender pale gray lizard of the Colorado desert of southern California even excels the fish and the frog, for it seems to have the instinct of always facing the sun when it stands upon a stone to gain a lookout. In this position both its color and its shadow coincide with those of the stone, and the concealment is perfect. The subject is one of tempting interest of detail, but enough has been said, perhaps, to make it evident that the dull colora- ASPECTS OF KINETIC EVOLUTION 2 I 5 tion of desert animals is a very complex phenomenon, not to be explained merely by coincidence, nor by environmental reac- tion, nor even by the selection of reactions. The possibility of developing such elaborate contrivances is not adequately conceived until we are able to think of the species as having an active instead of a merely passive evolution, until we recognize that species have internal as well as external reasons for continuing to put forth variations of all the charac- ters they possess, as long as the environment does not forbid. The endless possibilities of adjustment can then be realized, for the narrower the environmental road the more definitely adap- tive must be the evolutionary motion of the species. ORGANIC UTILITY AND ENVIRONMENTAL FORTUITY. The utility of new characters is not to be narrowly restricted to the environmental sense. New characters can be thought of as having what may well be termed an organic utility, quite apart from their effects upon environmental relations. They may afford a desirable stimulation like that commonly shown in the greater vigor of crosses between organisms not too unlike, and they may also contribute to the structural perfection and general efficiency of the organism. Both these effects of new characters would give the new type environmental and selec- tional advantages, but indirectly, and not to the exclusion of other more definitely adaptive contributions to constructive evolution. In the recognition of physiological values for new characters the kinetic theory of evolution diverges widely from the older doctrine that species are normally constant and stationary until changes are brought about by environmental influences. Al- though often misnamed dynamic, this conception was in reality static, for the organisms were supposed to have no power of change except as worked upon by the external causes. Never- theless, variations, even when ascribed to the environment, were often held to be merely fortuitous in their relations to evolution, for it was not believed that they would be preserved and accen- tuated except by natural selection. The development of useless characters could not be admitted under this theory, although it Proc. Wash. Acad. Sci., December, 1906. 2l6 COOK has become increasingly obvious that many of the characters which differentiate related species and genera are quite lacking in environmental utility, and probably always have been. Many characters which are now useful could have had little or no utility at the time of their inception unless they appeared suddenly in a highly developed state, as suggested by the now popular doctrine of mutation. The kinetic theory enables us to understand that during the earlier period, while a character has only an organic utility, it nevertheless tends to be preserved and to become more and more accentuated, in accordance with the principle of kinesis or prepotency of new variations and recently acquired characters, just as though the species were actively concerned to test the environmental possibilities of each of the new characters it may be able to develop. In this view there is no period in which the new character is entirely useless. Its continued develop- ment is normal and advantageous on the ground of organic utility, unless it happens to encounter some environmental obstacle which forbids further advance, or unless an excessive development is attained which weakens or unbalances the organism. In comparatively rare cases an acute natural selection may intervene and establish a standard for the species by eliminating all individuals which do not have a certain character developed to a required degree. If only one course of evolution remains open, progress in this direction may be greatly accelerated, for as the normal diversity of descent is eliminated the prepotency of the remaining variations appears to increase. This is not because the environment is hastening the perfection of a new form of fitness, but because it is of the nature of species to change, and to continue in the direction of further development of the characters already possessed. As far as environmental causes are concerned, there appears to be complete fortuity in the appearance and development of characters, except as selective specialization intervenes. This may occur, of course, at any time in the development of the character, and may lend it an environmental significance not possessed before, and perhaps not continued except for a limited ASPECTS OF KINETIC EVOLUTION 2\J period or stage of development. Thus the monkeys and anthro- poid apes seem to have secured from their larger brains no special advantage over other animals. No species of anthro- poids seems to have become very abundant or widely distributed. Only one member of the group continued brain-development to the point of utility in the struggle for existence, and gradually gained supremacy over the mundane creation. But mental development has by no means remained restricted to simple environmental requirements. Cerebral convolutions have con- tinued to multiply among the more specialized or highly civilized varieties of mankind until they have become, if recent statistics are to be trusted, a positive hindrance to the well-being of the species, like the overgrown plumage of the pheasants and birds- of-paradise, or the burdensome antlers of the extinct Irish elk. Civilized man is now facing a crisis in his own evolution. He must soon decide whether he will make use of his over-developed intellect for solving the problems which now beset his existence, or allow it to carry him entirely out of contact with his environ- ment and compass his destruction. As the supply of barbarous peoples of high mentality has almost run out, the present experi- ment of our race with civilization presents an element of histor- ical finality which adds, if possible, to the natural interest of such phenomena. All former civilizations of the European or Mediterranean peoples have proved suicidal. It remains to be seen whether the modern faith in science will be justified by the finding of means to avoid another repetition of history. Capable individuals tend always to assume parasitic habits and to become infertile, until the race is represented only by the relatively incapable immunes, upon whom civilization gets no hold. Science must make plain to capable people the folly of becoming parasites, or of permitting parasitism. Scientific dis- coveries have placed civilized man in many new relations with his environment, but these relations must have complete bio- logical adjustment if they are to contribute to the evolutionary progress of the race. Scientific discoveries have transformed the arts of production and transportation, but they have had no corresponding influences upon social organization. Luxury, idleness and over-education are dangers to society, not merely 2l8 COOK nor principally because they are connected with an unjust divi- sion of material wealth, but also because they rob the race of its most capable elements. However cruel and pitiful the fate of the incapable who are being eliminated in slums and factories, deterioration is no less real at the other end of the social series, and the loss to the race is far greater. Instead of dwelling, as has been customary, upon the fortuity of variations and of evolution, we might often gain a clearer insight by reversing the points of view and appreciating the fact that it is the environment which is fortuitous rather than the development of species. Whether a character be useful or use- less depends entirely upon the circumstances in which the organism is obliged to exist. Nowhere is this better shown than in man himself. The qualities necessary to a safe and prosperous existence in barbarism may be thoroughly disad- vantageous in a member of a civilized community. The only way in which the development of desirable qualities may be sub- stantially encouraged is by furnishing conditions in which they are advantageous, not, perhaps, in the way in which advantage is commonly reckoned, but in ways which shall conduce to the biological end of increasing, relatively at least, the better ele- ments of the race, instead of tending to eliminate them. The causes and remedies of these conditions are not to be considered here, the object being merely to illustrate from the history of man what is no doubt a general experience of species in nature, the change of the status of a character from useless to useful and then to harmful, depending upon this fortuitous relation between the character and the conditions. That only one species out of the millions which share with us the surface of our Earth should have developed intelligence, reason, con- sciousness, and personality, has appeared very strange, but it seems still more remarkable, when the vicissitudes of the journey are considered, that even this one should have reached so unique a distinction, and more mysterious yet that it should continue to climb the same summit far beyond any environmental or selec- tive requirements, and even in despite of such requirements. Nevertheless, we are but doing what other species of organisms and other races of men have done before, with the single excep- ASPECTS OF KINETIC EVOLUTION 2 1 9 tion, perhaps, of a better appreciation of the fate that is already befalling ns. Another highly specialized animal, the fig insect, affords an equally instructive illustration of the possibility that a character may develop past the point of fitness, and become dangerous to the species. The fig insects are much too highly specialized to be able to lead a free existence. They live only in the fruits of fig trees, which may very properly be said to have domesti- cated them as their only means of securing cross-fertilization. The two species, the insect and its fig tree, have thus a mutual interdependence of a very complete kind. In addition to their physical peculiarities, the female insects have the highly special- ized instinct to find the young fig fruits and to force their way into them, often with much difficulty and the loss of their wings, so that further flight is impossible. The utility of the insect depends finally upon the fact that it is stupid enough not to dis- tinguish between the male and female fig trees. The difference is a fatal one for the individual insect, for those which enter the female figs are lost. Their eggs never develop, and they leave no progeny, the perpetuation of the species devolving upon the relatively few insects which happen to reach male instead of female trees. Young male flowers are extremely scarce at the time when the principal generation of insects emerges, as though to definitely force them to carry pollen to the female trees. It is evident that the continued success of this method of pol- lination depends upon a very acute adjustment of the intelli- gence of the insects. They must know enough to seek, enter and fertilize the fig flowers, but not enough to distinguish be- tween those of the male and of the female trees. All of the insects which are really useful to the fig species in enabling it to ripen its seed are lost to the insect species, for their eggs have no chance of development. From the standpoint of the insect species there is an acute natural selection in favor of those which go to the flowers of male trees, but if there should anywhere be developed an instinctive preference for the male trees so that the fruits of the female trees remained unvisited, the fig would cease, in that region, to produce seed, and would become ex- tinct, along with its insect tenant. 220 COOK The selection which would eliminate the over-wise insects would not be applied to them directly, but to the trees which have become completely dependent upon their insect servants. Their highly specialized flower-receptacles are so tightly closed that no other insects will enter.1 When once such a delicate adjustment of structures and instincts breaks down, the parts are as useless as a watch that will not keep time. The utility de- pends only on the adjustment, and when the adjustment has become highly complex changes are far more likely to disturb than to improve it. Highly specialized types, those upon which selection has exerted the most successful influence, are ever the most liable to sudden and complete extinction, as geological history has already shown. Close adjustments induced by selective influence are not, in the long run, truly advantageous. The chances of survival are not increased by close adjustment, but by the continuation of development of characters which allow a wide range of possi- bilities of existence under different environmental conditions. From the standpoint of the species, changes of the environment are fortuitous, and the utility of adjustments is also fortuitous and temporary. Indeed, the study of adaptations alone might have suggested caution in the acceptance of the doctrine of en- vironmental causation, for a vast number of adaptations, and perhaps the majority of them, do not have reference to the en- vironment, but are devices for keeping the species together, that is, for facilitating symbasic interbreeding. To this class of sym- basic adaptations belong the whole series of specializations of flowers to secure the visits of insects, the group of phenomena which has probably figured more largely than any other as an evidence that adaptation is a genuine phenomenon of nature and not merely an elaborate collection of coincidences. These cross-fertilizing adaptations are real and wonderful, but the plants instead of having been acted upon by external influences have taken advantage of the environment to enable them to 1 A wild species of fig native in the Comitan district of the Mexican state of Chiapas has its fruits so completely closed that even the fig insects can no longer emerge by the natural aperture, but are obliged to bore through the wall of the fruit to let themselves out. Mr. W. T. Swingle informs me that this is true also of the sycamore-figs of the Old World. ASPECTS OF KINETIC EVOLUTION 221 maintain and extend the normal organization of the species. The individual plant gains no advantage from cross-fertilization ; the advantage appears only when the results are viewed from the standpoint of the species. FITNESS BY CORRELATION OF VARIATIONS. No one has appreciated more keenly than Darwin himself the limitation of his doctrine of selection in the way of providing new characters of fitness on which selection could work. He continued with persistence the search for adaptive significances of characters, and supplemented his discoveries in that direction by the hypothesis of the correlation of variations. This assumes that the characters which are being developed by selection carry with them the development of other characters, some of which may remain useless while others attain utility and thus become in turn the objects of selective education. It is as though charac- ters were fastened together in groups like chairs and tables so that they could be hitched along first by one leg and then by another. Instances of correlation between characters have been found, and the suggestion gains somewhat from the fact that mutations of independent origin often show close similarity although dif- fering from the parent type in numerous characters instead of in one only. Such a mutation might receive a selective advantage for one character, though the others would be preserved at the same time. Nevertheless, this suggestion would be subject to the same objection as the mutation theory as a whole, that the phenomena are abnormal and do not afford a true indication of the method of evolution in nature, for there the diversity appears not to be of the mutation type, but shows unlimited intergrada- tions of all the characters, as though to give absolute freedom in the making of truly constructive combinations. Correlations between different parts and tissues undoubtedly exist, but we may believe that they are brought about by normal evolutionary processes instead of supposing that characters have been tied up in arbitrary groups or bundles, which only explains one difficulty by imagining others still more mysterious. Such a character-complex would be, in effect, a suborganic organiza- 222 COOK tion, if such an expression maybe permitted. The hereditary- instinct or spirit of the species would be subdivided, like the spirits of the gods of the Japanese mythology. We would then need to speculate on the nature and relations of these subordi- nate entities whose only purpose, after all, was to stop a gap in a theory. While selection appeared as the only method of actuating evolutionary motion it was justifiable, perhaps, to use a charitable imagination on this suggestion of fitness by correla- tion, but in the kinetic interpretation, where it is perceived that selection is not the cause of evolution, the correlation assump- tion does not need to be invoked. It is excluded, as the logi- cians would say, by the law of paucity, a beneficent selection which eliminates unnecessarily complicated hypotheses. KINETIC ORIGIN OF ADAPTIVE FITNESS. Weismann's recognition of the noninheritance of " acquired characters" or "direct adaptations" destroyed the foundation of the older selective doctrine of evolution by environmental causation, and left the means by which adaptation had been attained a complete mystery, especially for those who continued to hold the other half of the doctrine of selection, that species are normally stationary. To logical minds it has appeared obvious that a new foundation must be found or that the whole doctrine of evolution must be given up, whence the special atten- tion given in later years to the " Origin of Fitness," in the hope of finding some way in which the external conditions can pro- duce heritable internal changes in organisms. If the present interpretation of the facts be correct, this is a completely insol- uble problem, or rather it is a gratuitous and artificial one, for there is no such relation as that which the selective school of " Genuine Darwinians" has hoped to ascertain. The non-inheritance of "acquired characters" proves that the changes which the environment " causes" are not those on which evolution proceeds, and forbids us to assert any directly causal connection between evolution and environment. Progress toward greater fitness arises and goes forward in quite the same manner as other forms of evolutionary change. The environ- ment establishes, however, requirements of fitness, at times very ASPECTS OF KINETIC EVOLUTION 223 rigorous with regard to some particular faculty or feature, but generally allowing wide liberty of chance and choice in other respects. The adaptations are seldom so close that no further beneficial or indifferent changes can be made. If we attempt, by artificial selection, to enforce too narrow restrictions and main- tain a closely uniform type, the effort always fails through the deterioration of the organism. The total fitness of species to their environments is simply the summary of their past histories. It has nothing in particular to do with evolutionary causes.1 The problem of fitness appears to be truly insoluble under the idea of normally stationary species. The postulates of the older selective doctrine are in direct logical agreement with each other, but one without the other is completely inoperative as a working hypothesis. Some have even denied adaptation because they despaired of explaining it, but all these difficulties disappear when the point of view is changed. Kinetic evolution supplies more abundant materials on which selection can act, and explains how fitness can come about without environmental causation. We are not obliged to discredit the evidence of our senses that adaptations exist, nor to reject the obvious probability that they are induced, though not caused, by the environment itself. All the difficulties are surmounted when we appreciate the fact that the environment works by the restriction and deflection of a normal evolutionary motion, and not as a direct or actuating cause. The environment furnishes certain specifications regard- ing what may be built, but builds nothing itself. Changes of the environments imply changes of the vital specifications ; they enable new evolutionary steps to be taken, but the species itself must originate and develop the appropriate variations before selection can favor them with its discriminating encouragement. The strength of the theory called Darwinism, that evolution is caused by natural selection, lay largely in the fact that it presented a solution of the problem of fitness, and could then explain evolution through adaptation. Darwinism was rational 'The word environment is itself the occasion of great ambiguity in evolu- tionary literature, some writers using it with reference to its supposed power to cause favorable variations, and others merely as a summary of selective influ- ences. Between these two extremes there are many gradations of emphasis, so that two writers may use the same words in expressing contradictory opinions. 2 24 COCK as a theory, but the facts have refused to sustain it. Subsequent efforts by Naegeli, Weismann, De Vries, and others to supple- ment or supplant selection as an evolutionary cause have failed to command general confidence, largely because they provided no logical or adequate solution of the fitness problem, and undertook to deny adaptation or to explain it away as a mere coincidence. The best that could be done under the static hypothesis was to suppose that if the new types happened to differ from the old in characters of greater adaptive utility they could survive, and, it might be, exterminate their parents. No means not wholly hypothetical were suggested whereby the environment could exert a definite influence upon the course of evolution. The kinetic theory more than makes good these deficiencies. It removes all need or temptation to minimize the extent of adaptation or the obviously very important role of selection in evolution. Though providing more generously than Darwinism itself the materials for selection to work upon, it does not carry us upon the dangerous ground of supposing that selection itself is an evolutionary cause, or that evolution is limited to adaptive characters. Darwinism assumed too much and explained too little. It predicated an important causal relation where none existed, and could still explain the evolution of adaptive char- acters only. Kinetic evolution assumes less and explains more. In recognizing the fact that the species are normally in motion it allows for the development of useless as well as of useful characters, and explains also how selection can contribute to adaptive specialization. SUMMARY OF INFERENCES REGARDING FITNESS. The problem of fitness is a crucial defect in the doctrine of evolution by selection, because in this theory selection does not become effective until enough fitness has been obtained to give a character selective value. The fact that organisms are often able to adjust themselves to different environments has been taken to prove that the environment causes variations of selective value. Environmental selection of these adjustment characters yielded the logically complete idea of an evolution initiated and actuated by environment. ASPECTS OF KINETIC EVOLUTION 225 The kinetic theory rejects the hypothesis of environmental causation of evolution as fatally discordant with the facts of organic nature. The individual members of species are normally diverse, even under the same conditions ; the fact that they may differ under different conditions is not to be accepted as a proof of environmental causation of evolution. There are two phenomena of organic fitness : first the adap- tation to environment afforded by the general characters of the species ; and second, the power often shown by individual plants and animals to adjust themselves to varied environmental conditions. The latter is a form of organic elasticity compara- ble, in a general evolutionary sense, to muscular contraction and locomotion, and with no special significance as a factor of evolution, nor any special pertinence as an example of the method of evolution. Both kinds of fitness are results of evolution, instead of being causes. They are fruits of the tree, not the roots. Fitness is maintained because evolution continues, not because the environ- ment works changes in organisms. For the static evolutionist, fitness becomes an abstract and insoluble problem. Viewed from the kinetic standpoint, it appears as a natural and neces- sary consequence of a spontaneous evolutionary motion con- trolled or deflected by selective influence. Environments continually change, and with them the relative utility of characters. A feature useless in one environment may be of value in another, or a useful character may become use- less or even detrimental, depending on external circumstances. There is thus a real and intimate relation between fitness and environment, but not a relation which can justify recourse either to natural selection or to direct adaptation, as causes of evolu- tion. It is not to be taken for granted that all the differences shown by plants or animals when environments are changed are in the direction of fitness. With different conditions and mate- rials, organisms build differently, or they may wander from the pathway of normal development in unwonted surroundings. Natural selection encourages fitness by preserving the fittest, but there are also environmental differences with no adaptive relation, and upon which selection exerts no influence. 226 COOK * To find that organisms differ in different environments is, after all, only to find that they exist, for where the conditions of existence differ the organisms must differ. The power of organisms to form adjustments is a measure of their ability to exist, for no environments are absolutely constant. Species strive, as it were, by every artifice at their command to enlarge their environments, to conquer more opportunities of existence. Now and then a successful combination is attained. Causes which can bring characters of selective value into existence can bring other characters as well, and can carry for- ward their development. It is no longer necessary to suppose that natural selection is an evolutionary cause at all, in the strict sense of the word. Selection may still be recognized as a con- dition or an influence in evolution, but there is nothing to show that evolutionary progress is actuated by selection. Fitness, in last analysis, comes by evolution, not evolution by fitness. Selection helps to explain adaptation, but it does not explain evolution ; it enables us to understand why evolution follows some courses and not others, but it does not show how the evo- lutionary advance is accomplished, nor how a new character can develop to the point of utility or harmfulness, so that selection can encourage or restrict it. The Lamarckian and the Darwinian theories ascribed evolu- tion to causes resident in the environment. The kinetic theory ascribes it to causes resident in the species. The causes of evolution are not to be ascertained by the solution of the prob- lem of fitness, but lie rather in the constitution of species and in the methods of organic descent. 2. INTRASPECIFIC DIFFERENCES AS MATERIALS OF EVOLUTION. The time has gone by when it was supposed that new knowl- edge could be gained by the analysis and rearrangement of old data and deductions. Nevertheless, it remains true that every advance in science requires, sooner or later, a new and consistent arrangement of the materials of investigation, and of the lan- guage to be used in describing them. Words are not things, but they often control the predisposition of the mind and thus obscure or illuminate the field of mental vision. ASPECTS OF KINETIC EVOLUTION 227 Science deals primarily with facts, and only incidentally with inferences or theories, though the latter are of immense use in helping to ascertain facts and test their causal relations. Useful theories arrange facts in what appear to be connected sequences, and enable us to project ourselves into the realm of the un- known without hopelessly losing our way in the maze of unre- lated data which we are otherwise likely to encounter. We follow the theory until we encounter facts which prove or dis- prove it, or until a more direct or more coherent theory has been suggested. Theories are like legislative enactments; the surest way to be rid of a bad one is to enforce it. A false theory, if studied with sufficient care will correct itself, because the places will be found where it is inapplicable. Moreover, the theories and laws which are the most difficult to repeal are those which contain a large measure of truth and justice, and which have been long in force, so that many vested interests have grown up around them. They take possession, as it were, of the field of investigation, divide it up and place on guard a multitude of technical terms and distinctions which defend the approaches of the citadel of error by a battery of words, which go far to keep a new idea unintelligible. The prevalent doctrine that evolution is caused or actuated by natural selection is such a theory, containing a large and impor- tant truth, and at first immensely fertile in scientific results and practical applications, but essentially erroneous, and in some fundamental respects dangerous to agriculture and to man himself. The basal axioms, the things taken for granted in the selec- tion theory are (i) that species are normally stationary and con- stant in their characters and (2) that their evolutionary progress is caused by the environment, but neither of these assumptions proves to accord with the facts. It has not been shown that either environment itself or the selection which it exerts are true, efficient causes of evolution. Neither has evidence been found to prove that a species has ever remained stationary in all its characters, or that the component individuals tend to become "exactly alike," even under the most uniform conditions. 228 COOK Nature abounds in striking evidence of the alternative kinetic view that species are normally in motion, and that the individual organisms of which they are composed have a normal and necessary intraspecific diversity, quite independent of environ- mental influences. Moreover, there is reason to believe, from the prevalence of sexual and other diversities inside the specific lines, and from the degeneration which follows attempts at maintaining a stable and uniform type, that diversity among individuals of a species is not only universal and normal, but necessary and advantageous. The prevalent doctrine that evo- lution is caused or actuated by natural selection has been char- acterized as a static theory because species are thought of as normally at rest, that is, as stationary or constant in characters and tending to be uniform as far as external conditions will permit. The causes of variation and of evolution were sought in the environment and not in the species itself. The problem was to show how the external causes produce the internal effects, but the task was hopeless from the beginning, for the variations which the environment causes are not those through which evolution goes forward. It is apparent, therefore, that the abandonment of the static point of view, and the placing of a new interpretation upon a large class of familiar facts calls for a new plan for the study and discussion of the phenomena familiarly called variations, in the older and looser sense of the term, meaning all the differ- ences to be found among the individuals of a species. Differ- ences not caused by environmental influences were, of course, quite unconsidered in static theories and classifications. There was not even a scientific term for this universal phenomenon of intraspecific diversit}-. A complete treatment of the subject would involve the rear- rangement of a large part of the data which have figured in the evolutionary literature of the last half-century. The scope of the present statement permits only a brief and imperfect outline. It is not possible even to adequately describe and illustrate the details of the facts of original observation to which reference is made. Particular instances are not given, therefore, with any idea that they are adequate to demonstrate the truth of the inter- ASPECTS OF KINETIC EVOLUTION 2 29 pretation which has been put upon them. They serve only as samples of groups of facts to which the interpretation is applic- able, the primary object being, not to demonstrate conclusions by formal arguments, but to indicate a standpoint, the correct- ness of which may be judged by other observers from the facts encountered in their own fields of investigation. To learn the nature and causes of evolution it has not been sufficient to explore and explain the barriers between the species. It is necessary to go inside the species and to ascertain, if pos- sible, which of the many differences between the component individuals represent forward steps in organic development, and which mere lateral diversions or displacements. DARWIN'S DISCOVERY OF VARIATION. Much has been written to show that Darwin did not discover evolution, as popularly supposed, since the idea may be traced back to the Greek philosophers or to the Hindus, and had been entertained in modern times by Lamarck and several others of Darwin's predecessors. And yet, the popular impression, though perhaps inexact as to technical terms, is more just than that of many scientific critics. Darwin was able to secure general interest and confidence in an idea previously indefinite, intangible and practically useless. If Darwin did not discover evolution or even invent entirely new arguments in its favor, he performed a more valuable and unique service in establishing the fundamental fact of variation, without which all evolutionary ideas would have remained empty and sterile speculations, as they had remained during the two thousand years preceding. Darwin discovered what is still more important to the scien- tific world than the abstract idea or theory of evolution, namely the means of evolution, which is variation. Darwin was the first to adequately appreciate the fact that species do not consist of individuals identical in form or structure, but of those which are diverse, each different from the others in a greater or lesser degree. Upon the fact of variation Darwin also based his theory of evolution by natural selection and other environmental causes, a theory which has had great popularity in the general scientific world, because it afforded the most concrete suggestion 230 COOK regarding the nature of the causes of evolution. It is desired therefore, to distinguish clearly at this point between the facts of variation first adequately recognized by Darwin and the theory of environmental causes of evolution often called Dar- winism. Naturalists do not all believe in environmentally caused evolution, but nearly all are now agreed in thinking of species, not as single morphological points, but as large groups of similar individuals. Since the time of Darwin it has been believed that evolution has been accomplished by means of variations, but there is still the widest divergence of scientific opinion regarding the kinds of variations which cause or contribute to developmental changes. Some theories depend upon one or another of the different kinds of variations and ignore the others, and some hold that all varia- tions are caused by the environment and that evolution itself is merely a summary of environmental influences. Many writers have approached the subject from the stand- point of formal definitions and narrowly technical distinctions, but the practical divergences between the different views become most apparent from the types of variation — the kinds of intra- specific differences — upon which they depend as showing the nature of evolutionary motion. To correctly fix upon the kind or kinds of variations which contribute to evolution, is the first step of progress toward knowledge of the true evolutionary factors, and brings us by the most direct route to the determina- tion of the primary question, whether the true, efficient causes of evolution lie in the environment or in the organisms them- selves. Are the variations which are induced by the environ- ment those by which evolutionary progress is accomplished? In Darwin's original suggestion environment was held to bring about evolution, first by inducing variations and then by selecting those which proved to be advantageous. The environ- ment was considered as at once the cause of variations and of evolution. This view is still generally accepted as the teaching of science regarding organic evolution, although many modi- fications and collateral suggestions have appeared necessary to Darwin himself and to many of his successors. Some have approached the Lamarckian idea of direct adaptation, in ascrib- ASPECTS OF KINETIC EVOLUTION 23 1 ing much to the moulding influence of the environment, and in requiring correspondingly little of selection. Other writers have gone to the opposite extreme, making little of environmental factors and much of natural selection of fortuitous individual variations. The latter tendency has been dominant since Weis- mann showed that "acquired characters," the results of direct environmental influences, are seldom or never inherited. In the original Darwinism and its various amended forms there seems usually to have been included the tacit assumption of a constant of variability. It is taken for granted that a cer- tain amount of variation shall be manifested by each species, so that selection by paring off the species on one side can cause it to grow out on the other, and thus compel a gradual change of characters. Without selection the average is thought to remain stationary, and if selection be withdrawn the progress already made may be lost by retrogression. Selection, in this view, is the true actuating cause or principle of evolution. Mivart, and recently many others, have considered that both the environmental variations and the minute and fluctuating indi- vidual differences were alike in adequate to accomplish evolution through selection, and have advocated a return toward the older doctrine of special creation. They hold still to the evolutionary idea that species arise one from another, but suppose that the new types originate suddenly by " extraordinary births," or by abrupt mutative variations, that is, by individuals which depart widely from the type of the older species. The occurrence of many such abrupt variations is a definitely established fact. Among plants they often come true to seed, and among animals they are often prepotent when bred with other members of their own variety or local species. Nevertheless, it does not appear that this is the method by which species originate in nature. The prepotency of new variations indicates the probability that old species are tranformed by this means rather than that new species are abruptly originated. Darwin appreciated better than many of his successors in the field of evolutionary literature the fact that variations are of many kinds, of very different evolutionary significance, and due to many different causes. As an evolutionary pioneer it was Proc. Wash. Acad. Sci., December, 1906. 232 COOK a sufficient service to have shown that enough variation exists to make evolution feasible or even plausible. The scholastically educated public, which often appreciates arguments much better than facts, was obliged to approach evolution through Darwin's deductions rather than through his perceptions. Evolution was accepted or rejected on the merits of natural selection, though the two ideas have no necessary connection. Natural selection and evolution are both facts, but in proving that the one is the adequate practical cause of the other it would be necessary to show that the variations through which evolution goes forward are caused by natural selection. No such causation has been demonstrated. Natural selection does not furnish the variations nor explain why variations are accumulated and carried for- ward into evolution. It only explains why some variations are preserved instead of others. It does not explain evolution, but shows how the direction of evolution may be influenced by the environment. The causes of evolution, or, to be more explicit, the causes of evolutionary variations, are as mysterious to us as they were to Darwin, and indeed, more so, since the greatest step in evolutionary investigation since the time of Darwin has been a negative one, the destruction of the theory of the inher- itance of characters acquired from the environment. Darwin sometimes placed much importance on variations induced by environment, and invented the theory of pangenesis to explain the inheritance of such, and bring them within the field of nat- ural selection. Without pangenesis and direct inheritance, nat- ural selection loses its place as a positive factor in evolution and becomes purely negative ; it neither causes variations nor causes them to accumulate. The most that can be claimed is that it hastens the development of some characters by retarding others, or by forbidding them entirely. It is apparent in some groups of organisms that the influence of natural selection has been very great, in others that it has been very small,1 but its effects are in all cases dependent upon the underlying facts, that variations do appear and are accumulated. Natural selection does not explain evolution, except in a very loose and super- 1 Cook, O. F., 1902. Evolutionary Inferences from the Diplopoda. Proc. Entomological Society of Washington, 5 : 14. ASPECTS OF KINETIC EVOLUTION 233 ficial sense ; the first step toward a better solution of the riddle is to reorganize the vocabulary of variations so that it can be used to express something more than erroneous deductions from natural selection. Many words and distinctions of use in pre- senting the idea that natural selection is a true, actuating cause of evolution, may be spared, but there are others whose utility is not destroyed by this change of view. VARIATIONS AND INTRASPECIFIC DIFFERENCES. Before entering upon a discussion of a general scheme of variations it is necessary to notice a fundamental error commonly attached to the word variation itself. Most of the exponents of selective theories of evolution have made, either tacitly or avowedly, the assumption that all the individuals of a species are normally alike and tend to remain uniform, and that the differences found among them are of external origin and of the same nature as the differences between species, and hence of evolutionary significance. It has been assumed, in other words, that all the differences to be found among the members of a species are variations in the evolutionary sense, and hence that a cause of difference among the members of a species is neces- sarily a cause of the evolution of species. It is not too much to say that this assumption of normal specific stability and uni- formity, either absolute or within constant limits, begs in advance the whole question of the nature and causes of evolutionary change. Notwithstanding the popularity it has enjoyed, this static idea of species is worthy of no more respect than any other unsupported hypothesis. For the former purposes it appeared desirable to divide the variations, that is, the differences to be found among the individuals of a species, into two classes — (i) those with which they are endowed at birth, and (2) those which they acquired later from the external conditions of their existence. Variations were classified, in other words, as either congenital or acquired. The distinction is not illogical, but it has proved worse than useless for evolutionary purposes, because the static theory by which it was suggested was an erroneous assumption. Many objections to natural selection, or to evolution as based 234 COOK upon it, have been raised from the time of Darwin to the pres- ent day, but a doctrine with so many merits was not to be dis- placed until another could be found. Furthermore, the alterna- tive views hitherto presented have shared either one or both of the false premises of natural selection, or they are built, like that theory, on some one group of biological phenomena, and leave out of account other data equally pertinent to the general conclu- sion, and equally in need of evolutionary explanation. One of the ways in which the search for evolutionary causes went far afield was in assuming a close and essential relation between evolution and the origin of species. It was thought that if it could be known how new species came into existence the secret of the diversity of nature would be revealed. As a mat- ter of fact evolution has very little to do with originating or multiplying species. The evolutionary process continues, we may believe, whether the group becomes divided or not. The two parts become different because evolution continues in both, but it would also have continued if the separation had not taken place. Isolation, of one kind or another, is the cause of the multiplication of species, but not of evolution. We would gain no special advantage for evolutionary observation by stationing ourselves at the point of bifurcation of one group into two ; the only lesson would be that isolation isolates, that segregation segregates. Evolution, it cannot be repeated too often, does not take place in the gaps which are left between the species, but inside of the species, among the interbreeding organisms ; it is an zWrtfspective phenomenon, not interspecific. To learn how species differ is only to ascertain what roads they have traveled over, it is only by canvasing the differences between the individuals of a species that we can hope to ascer- tain how the evolutionary progress is accomplished. It will not suffice, when when we find that the individuals of a species differ in a certain respect, to assume that this is the line of evolution- ary advancement. We must be content first to recognize and describe the several kinds of intraspecific differences before we can hope to estimate with confidence the contribution of each form of change to the general and permanent progress of the species. ASPECTS OF KINETIC EVOLUTION 235 CLASSIFICATION OF INTRASPECIFIC DIFFERENCES. Intraspecific differences may be classified by reference to three considerations ; the nature of the diversity, its origin or occurrence, and its relation to environmental fitness. Such a classification is open to the objection that it requires an advance decision upon the evolutionary bearings of the facts which are being classified for evolutionary purposes. This objection also applies, however, to all preceding efforts at classifying vari- ations. Such classifications have no value, of course, as the basis of arguments. Their use is purely that of permitting an orderly arrangement of materials and of illustrating distinctions. They aid in discrimination, not in demonstration. The utility of the proposed arrangement may be best appreci- ated by thinking of it, not as a classification, but as affording points of view or avenues of approach to the study of the intricate complexities of evolutionary problems. The purpose of physio- logical study is not classification, but the comprehension of causal relations. Differences oj Growth Stages. — Changes of size, form, structure, and function shown in the life-history of normal mem- bers of the species, including metamorphosis and alternation of generations and structural phases. The forms of diversity grouped under this head would not be called variations except in the most general sense of the term, but they must be taken into account in making a complete outline of intraspecific dif- ferences. Differences of Normal Descent (Heterisni). — Individual and other differences, including those of sex and polymorphism, which appear among the members of the species under normal conditions of interbreeding in the same environment, and even among the simultaneous offspring of the same parents. Differences of heterism have no relation to accommodational fitness, though they may assist in the evolution of adaptive characters. They have sometimes been called fortuitous or fluctuating variations because they had no apparent utility, the organic advantage of diversity of descent not having been recognized. Differences of Accommodation to Environment (Art ism). — 236 COOK Differences resulting from the ability of individual organisms to adjust or accommodate themselves to different environments. These are the variations which have the most intimate connec- tion with the environment, though they have no special signifi- cance as causes of evolution. Differences of Deficient Accommodation (Topisni) . — Differ- ences resulting from the inability of organisms to fully adjust themselves to special conditions. The result is a non-hereditary divergence from the normal characters of the species. Differences under New Conditions (NeotoJ>ism) . —Vari- ations induced by the transfer of organism to new and unwonted conditions. Three stages of new place effects may be distin- guished, (1) those in which there is merely a stimulation of growth, (2) those in which there is also a definite mutative change of the hereditary characteristics of the variety, (3) those in which the new conditions call forth a promiscuous mutative diversity. Differences of Partial or Recent Interruption of Inter- breeding {Porrisni). — Differences arising from the unequal distribution of variations, that is, from a recent or partial inter- ruption of interbreeding. Such are the differences that exist between individuals from the remote parts of the range of a species (geographical differences) and the differences of segre- gated local varieties of domesticated species. The nature of these differences is the same as that of the differences between species. They are the result of divergent tendencies of evolution. Differences of New Genetic Variations (Neism). — Prepotent variations which arise under normal conditions of free inter- breeding, without having existed previously among the ancestors of the variant individuals. They can be preserved without isolation, and are the characters which probably contribute most to heterism, and to the normal evolutionary progress of species in nature. There is no evidence that the appearance of such variations has any connection with adjustment or environmental fitness. Their preservation depends, of course, upon their being useful, or at least not positively detrimental. Differences of Aberrant Heredity ( Teratism). — Failure of the organism to attain the normal form, structure or size of the ASPECTS OF KINETIC EVOLUTION 237 species. Teratism occurs whenever there is any accidental deviation from normal developmental processes, whenever con- ditions change beyond the practicable limits of normal adjust- ment, and whenever the specific network of descent is abnor- mally narrowed. Thus there are many kinds of teratisms, and manj^ gradations between them and the other more normal kinds of variations. Mutations are abnormal or teratic neisms which appear abruptly in inbred or narrowly segregated groups, and which require isolation in order to be preserved. Even when in- duced by changes of environment, mutations are to be reckoned as aberrations rather than as accommodations. This classification makes no claim to final completeness, since still other kinds of intraspecific differences may be discovered. No doubt the schedule will appear to some as already too extensive and complex, but it will be evident that none of the alleged kinds of differences can be left out of account with- out misinterpreting one or more of the other groups of phe- nomena. To overlook the facts of heterism would make hope- less confusion under artism, topism and neotopism. To fail to distinguish between neism and teratism is to mistake degenera- tive mutations for examples of progressive evolution. Characters, in the morphological sense, cannot be classified and catalogued as heterisms, artisms, or teratisms. There is an intimate and even interchangeable relation between these differ- ent kinds of differences. An individual may be larger than others of its species, either as an inheritance or as a new vari- ation, or because the conditions are favorable, or even because they are new. Finally its greater size may be abnormal, or of the nature of a monstrosity. The same character may thus have great diversity of evolutionary significance. DIFFERENCES OF GROWTH-STAGES. Under this class of intraspecific differences it is proposed to include all the general forms and growth-stages in which the members of a species normally appear in any part of their life history. Only in the lowest and most primitive groups do all the separate, individual organisms belonging to the same 238 COOK species have even a general similarity of structure and external appearance. There have been extensive and not altogether profitable dis- cussions of the relation of growth-characters to those of the adult and to the evolutionary history of the species. The older em- bryologists worked out a doctrine of recapitulation to explain larval and juvenile characters, but it is evident in some groups, such as the insects, that preliminary stages may be quite as adap- tive as the adult form of the species, and sometimes distinctly more so. The differences of growth-stages are themselves of very different types in the various natural groups, as a result of the great diversity of methods by which evolution has been accomplished. THREE TYPES OF CELLULAR STRUCTURES. The most fundamental diversity of form and structure which exists among the members of the same species is that which arises from the existence of different types of cell-organization. In many of the lower groups of plants the vegetative organism, like a filamentous alga or a moss-plant, is composed of simple cells which have not conjugated and which have in many cases no power of conjugation. In the higher types of plants and animals the body of the organism, in its highest and most com- plete form, is built up of cells in a double or conjugating condi- tion. The higher fungi differ from the ferns, flowering plants, and higher animals in that the cells associate themselves while in the first stage of conjugation, before the nuclei have fused, while the cells of the other groups represent the second stage of conjugation. The nuclei have fused, but the chromatin gran- ules still remain distinct.1 The great diversity of the cells which compose the bodies of the higher plants and animals may be viewed as a phenomenon of social organization. The lower the organism the more alike are the cells until in the lowest all cells are similar and equal. Where socialization, the habit of joining together or living in groups, has not progressed too far, the cells of compound indi- 1 Cook, O. F., and Swingle, W. T., 1905. Evolution of Cellular Structures. Bulletin 81, Bureau of Plant Industry, U. S. Department of Agriculture. ASPECTS OF KINETIC EVOLUTION 239 viduals may still be alike ; the organization is still a mere gre- garious association. Later, there may come about a division of labor among the cells, and a corresponding diversification of structure and form. The common pond-scum (Sftirogyra) con- sists of threads formed of cylindrical cells, joined end to end, and all alike in their vegetative and reproductive powers. Another similar organism (CEdogoniuvi) consists, for the most part, of similar chains of equal cells, but these have only vege- tative functions. The power of reproduction has been restricted to two kinds of special sexual cells different from the vegetative cells. Advance in the scale of organization not only maintained this distinction between the reproductive and vegetative cells, but continued to increase the numbers and differentiate the struc- tures and functions of the latter, until the immensely complex bodies of the higher plants and animals had been built up. The primitive type of cell organization, that which built up the filaments of the lower algae and the vegetative tissues of the liverworts and the mosses was not able, however, to reach the higher possibilities of cellular structure. The cells which com- pose the bodies of the higher fungi have two nuclei, and those of the flowering plants and higher animals have two sets of chromosomes. These double-celled conditions have arisen through a lengthening out of the process of cell-conjugation as it occurred in primitive types like CEdogonium. Instead of conjugating at brief and distant intervals, the cells which com- pose the bodies of the higher plants and animals are in a condi- tion of prolonged conjugation, the cell fusion which begins when the egg-cell is fertilized by the sperm not being completed until after the whole compound cellular structure has been built. Several groups of plants have two structural phases, one built of the primitive simple type of cells, the other of the double or sexual type. The moss-spore, when it germinates, first produces a delicate tube like a pond-scum, and the fern-spore a small plate of simple cells, much like a liverwort. These diverse stages or phases of structure of the same organism have usually been described as alternation of generations, but the case is in reality entirely different from the phenomenon of alternation found among animals. 24O COOK ALTERNATION OF GENERATIONS (METAGENESIS). In many animals and plants the usual method of propagating new individuals by new sexual conjugations gives place to a more or less regular alternation with generations which are propagated vegetatively, or without a new conjugation. Among the animals, such as the tunicates and plant-lice, the generations which propagated vegetatively have a form different from those which propagate by renewed conjugation. Alternation of generations, in the proper sense of the words, occurs when the same species exists in two alternative forms, and especially where the two forms have different methods of propagation. The plant-lice furnish the most familiar example of alternation of generations. We may suppose that, like other insects, they were confined originally to normal sexual repro- duction, but their evolution has been in the direction of smaller size and simpler structure, and they have also developed the power of multiplying for several generations by partheno- genesis, the parthenogenetic generations being further distin- guished by the absence of wings, and by being very short-lived. At the end of the season winged insects of both sexes are pro- duced, and normal fertilization and egg-laying ensues. No such alternation of sexual and parthenogenetic generations is known to have arisen among plants, though a similar interpre- tation might be placed upon the bamboos, for example, which propagate vegetatively by the branching of their root-stocks for a long series of years. Then all the plants of the species blos- som, bear fruit and die, at the same time. Each sterile shoot of the bamboo might be interpreted as parthenogenetic genera- tion if compared with the sexually propagated generations of a plant like Indian corn. METAMORPHOSIS. Among the insects in particular, and to a somewhat less de- gree in many other animals (mollusca, Crustacea, batrachia, fishes, etc.). pronounced changes of form and structure, some- times very abrupt, take place during the life-history of each in- dividual. Thus caterpillars change by metamorphosis into butterflies, grubs into beetles, maggots into flies, tadpoles into frogs, etc. ASPECTS OF KINETIC EVOLUTION 24I Metamorphic differences are largely adaptive, but it is none the less probable that the alternation of bodily forms and the change of food and environment may contribute something to the same physiological results as diversity of descent. In the more specialized insects metamorphosis is accompanied by a complete disorganization of the larval tissues, the pupae repre- senting, as it were, a return to the egg stage, the change of ex- ternal form affording an opportunity for a complete rebuilding of the cellular structure of the body. It may be that this fact, viewed in connection with the extremely complex nuclear organs of the cells of insects, will assist in explaining the unique effi- ciency of the insect organism. Metamorphosis is not restricted, however, to animals. In plants like Eucalyptus and Junificrus there are sudden changes of form and structure from the juvenile to the adult phase of the species. HETERCECISM. Many plant and animal parasites infest two or more hosts in different stages of their life-history. Changes of hosts are then usually coincident with metamorphoses, or with change of gen- eration or of structural phases. It has been inferred by some that the abrupt change in the organism is due to the change of food and other conditions of existence, but this does not find confirmation in the studies of the life-histories of the parasites. The indications are more favorable to the opposite suggestion that the great diversity of conditions has enabled the parasites to proceed on two or more independent courses of evolution. The parasites have developed the power of living in two or three distinct environments at different periods of their life- history, and the characters which adapt them to this variety of conditions have been attained, apparently, in quite the same manner as the characters of other less specialized plants and animals. The more primitive simple-celled stage, or haplogamic phase, of many species of rust-fungi is confined to pines or to others of the more primitive families of plants, while the more advanced and efficient double-celled phase of the parasite has been able to attack plants of more highly developed families, 242 COOK such as the Leguminosae or Composita?. There can be little doubt in such cases that the evolution of the later phases of the parasites have taken place in coincidence with the advancing development of their host-plants to which they are so strictly confined. GROWTH SPECIALIZATIONS ARISING FROM SOCIAL ORGANIZA- TION (politism). Just as cells have become diverse by specialization in the build- ing up of compound cellular structures, so individual organisms of the same species may become diverse under conditions of social organization, that is, when the individual organisms do not live singly and independently, but in groups, colonies or compound individuals. The bionomic unit of such species is no longer the individual but the colony, since it is only in the colony form that it meets its environmental problems or enters into relations with other species. A good illustration of politism is to be found among the compound types of higher plants, those which take the form of shrubs or trees and consist of aggregates of large numbers of the individual twigs or branches which cor- respond to whole individuals of simpler types. The primitive herbaceous types of flowering plants have a root and a stem, the latter with a series of leaves and a flower at the top. If this be considered an individual, larger plants with many stems or branches and many flowers are compound individuals. Each branch or flowering twig of a tree may be thought of as corresponding to the small individual herb. Usually the branch-individuals are all of one kind, or at least equivalent and able to replace each other, but in some species such as cacoa, coffee, cotton and the Central American rubber tree (Castillo.) the branches are strictly dimorphic, that is, of two or more distinct kinds with different forms, structures and func- tions, and also taking definite positional relations in the building up of the compound individual plant or tree. It is among the animals, however, that specializations of poli- tism exist in vast variety, and the diversity becomes obvious and familiar. In many different groups there have grown up social organizations, so that all stages may be found between the ASPECTS OF KINETIC EVOLUTION 243 merely gregarious condition in which the individuals are still equal and alike, to those in which the diversity inside the same species may be greater than that of genera and families in other groups. In man himself social organization has scarcely gone farther than the gregarious state, though some races of man- kind have more pronounced social instincts than others, and such instincts have undoubtedly been important factors in their progress or backwardness in civilization. In some countries distinct castes exist, but these are racial or historical in origin and scarcely amount to the attainment of intraspecific diversification. By far the most compact and highly specialized forms of social organization are to be found among the insects. Re- markably similar conditions have been attained independently in several different families belonging to two very different orders, the termites and the hymenoptera. In these highly specialized insects the individuals of a species are no longer capable of independent existence, but, like the cells of the higher plants and animals, have no meaning except as parts of a collective, super-individual organism. The nest or colony has become the true unit of the species, and its members are differentiated into numerous castes adapted to particular func- tions by pronounced differences of size and structure. Among the hymenoptera only the females have social instincts and take part in the labors of the nest or the hive, but among the termite both sexes are equally involved. Reproduction is restricted to a single royal pair, who do no work beyond burrowing in the ground after their first and only flight. The king and queen and their numerous progeny are fed and cared for, and the architectural and agricultural labors of the state are performed by hosts of sterile dwarfs, of which in some species there are as many as four different castes — soldiers, foremen, workers and nurses, each distinct in form and highly specialized in instincts for its particular part in the labors of the city. The body of the termite queen may be hundreds of times the size of that of a worker, and the head and mandibles of a soldier twenty times as large as those of a nurse. Termite communities often contain millions of inhabitants. They build structures far exceeding, proportionally, anything attempted by man, and 244 COOK maintain underneath them immense systems of subterranean fungus gardens and chambers for storing and curing the com- minuted wood of which the gardens are built. This material is brought in from long distances by means of tunnels bored through the earth or covered passages built over rocks and tree trunks. Politism is to be classed as a specialization of growth-stages, because among the bees, at least, it has been found that the differentiation of the sterile worker from the fertile queen is determined by the amount and quantity of food given to the growing larva. It is difficult to believe, however, that this is true of the termites, for the young are not stationary grubs as among the bees, but active creatures which circulate to all parts of the nest, so that a consistent policy of feeding seems quite impracticable. Moreover, the workers and other sterile castes of the termites are not undeveloped females alone, as among the bees, but consist of stunted forms of both sexes. DIVERSITY OF NORMAL DESCENT (HETERISM). The individuals of a specific group may appear closely alike when compared with those of other species, but when compared with each other their diversity becomes obvious. Many evolu- tionary writers have believed in a principle of heredity which would make all the members of a species " exactly alike," and have then assumed that intraspecific diversity is due to varia- tion of environmental experiences in one stage or another of the life-history of the differing individuals. The kinetic theory depends upon neither of these hypotheses, but recognizes the diversity of individuals inside the species as a normal and highly significant evolutionary phenomenon, for which the term heterism has been proposed. Plants and animals propagated under the same conditions may appear more similar than others of the same stock grown under diverse conditions, but they do not tend to any complete uniformity except as this is brought about by the abnormal inbreeding to which domesticated vari- eties are usually subjected. Heterism might be defined further as the morphological aspect of symbasis. To support and hold together the organic ASPECTS OF KINETIC EVOLUTION 245 structure there must be an interweaving of lines of descent among diverse individuals. This requirement is most conspicu- ously met by the familiar phenomena of sex-differentiation, but can be traced upward through all the intermediate stages from simple heterism, or mere individual diversity. As manifestations of heterism are to be included all stages of intraspecific diversity, from individual differences to the extreme specializations of the sexes and polymorphic forms of the higher plants and animals. The function of heterism is to afford diver- sity of descent, under conditions of symbasic interbreeding. Narrow segregation or selective inbreeding tends to eliminate heterism, but with the inevitable result of degeneration. Heteric characters are highly heritable and though sometimes affected by environmental conditions are in no way dependent upon them or caused by them. Purity of stock and uniformity of characters are not syn- onymous terms, as commonly supposed. A very "pure " inbred strain may degenerate and become inconstant through mutation, or there may be the diversity of dimorphism or polymorphism in a species or variety which has not been crossed with any alien blood. Heterism, in its most general and unspecialized sense, is what has been called by some authors individual variation or fluc- tuating variation. It includes the regular and normal individual diversity of the memhers of a species which is not induced by differences of external conditions. Some writers do not admit that there is any such diversity, not caused by external conditions. It is very difficult, of course, to say that any given character or difference may not be connected with an environmental change, but it is very easy to ascertain with reference to most of the so-called individual differences, that the environmental relation, if any, is not at all constant, and not to be established on the basis of any form of scientific observation yet suggested. We are perfectly aware that the children of the same parents, born and raised under the same roof are often very unlike, while on the other hand, close family likeness may persist between children born and bred in remote parts of the earth involving the completest possible change of climate, food, and other con- ditions of existence. 246 COOK Intraspecific differences, or variations, as they have been called, have been interpreted hitherto either as results of envi- ronmental influences or as steps toward evolutionary change. The recognition of heterism, or the diversity of normal symba- sic descent, is incidental to a third explanation of the value of variations, that they help to maintain the vital strength or organic efficiency of the species. Indeed, the frequency and extent of the differences of sexes, castes, races and alternating generations show not onlv that organisms may change without being divided into separate species, but also that diversity inside the species has an evolu- tionary as well as an environmental significance. Heterism has, if this suggestion be well founded, a concrete physiological value in the economy of the species, quite as real as food and water, though of a different kind. The fuel and water are necessary to keep the engine going, but it is also necessary that the machine be kept in repair and from time to time replaced by another built on the same plan. Environmental variability or power of accommodation, en- ables the species to operate under a variety of external condi- tions, but heteric variability provides diversity of descent, even under uniform and favorable conditions, and thus makes it pos- sible for the species to continue to produce new individual organisms as good or better than the old. Theories of evolution by environmental causation have over- looked heterism and have assumed that the individual members of species would be alike if there were no environmental in- equalities to make them different. This assumption is con- trary, however, to all the pertinent facts observable in nature. Acquaintance with the members of any wild species of plants or animals soon shows that individual differences exist, as great, and often greater, than those recognized everywhere among men and women, or among horses, dogs, tulips, roses, grape- vines or apple trees. Definite individual diversity, as of stature, features, and thumb marks is not confined to the European races, nor to the human species. Travellers newly arrived in Africa or China often have the impression that the natives are all closely alike, but with longer residence they appear as different as Europeans. ASPECTS OF KINETIC EVOLUTION 247 Likewise with plants and animals ; it is necessary only to become personally acquainted with them to appreciate their individual differences. The shepherd knows all his sheep as individuals, also the poultry-raiser knows the eggs of the indi- vidual hens, and the farm boy knows the kind of nuts which each hickory tree produces. An instructive instance of natural heterism was observed in a species of agave which is extremely abundant on the mountains to the north of Chiantla, in the department of Huehuetenango, Guatemala. The size, shape, color and spine-development of plants growing by the hundreds along the roadside varied end- lessly. Some were pale-green and heavily pruinose, some slightly pruinose and much darker green. Some tapered rather gradu- ally to the point, some carried their width to near the end. On some the spines were very numerous and prominent, on others scattering and small, and with all grades and combinations of these and other varying characters. It is not claimed that these agaves have essentially greater individual differences than other plants. The phenomenon of heterism is rendered unusually striking because their large leaves have a very definite form and are closely alike on the same plant, and thus give unusually favorable opportunities for observing and comparing the differ- ences which exist. SPECIALIZATIONS OF HETERISM. The recognition of the facts of heterism, the existence of intraspecific diversity for its own sake, and of its own physio- logical value to the species might appear to rest on merely theo- retical ground were it not for the many specializations of heterism for which no use or meaning has even been imagined, other than that of maintaining a desirable diversity of descent. In some species heterism has remained unspecialized. The individuals are different, but still all equivalent and alike, pos- sessing all the essential vegetative and reproductive parts. Such species secure the benefits of heterism only by the introduction of new characters, for each character can be shared ultimately by all the members of the species and thus ceases to be of value as a means of maintaining diversity of descent. Proc. Wash. Acad. Sci., December, 1906. 248 COOK Heterism becomes specialized when there are permanently established differences among the members of the species, as in the familiar phenomenon of sex. There is also a series of many gradations between unspecialized heterism of merely individual differences, and the fully established sex-differentiation. The separate sexes of the higher animals are so familiar a phe- nomenon that we have been satisfied to consider them merely as incidental to the process of reproduction, and have thus over- looked the additional physiological value of sexual differences as specializations of heterism, to insure diversity of descent. In man himself and the higher mammals and birds the prin- ciple of sexual selection enunciated by Darwin may have had an influence in the further accentuation of sexual differences such as beards, wattles, combs, tail-feathers and other means of rendering one sex or the other conspicuous and thus attracting their mates, but secondary sexual differences are not confined to the higher groups or even to animals. Many plants are unisexual and the two sexes often have differences other than those of the essential organs. As the two sexes of plants neither see nor come near each other, the pollen being carried by the wind or by insects, there can be no question of sexual selection here. Even types as lowly as the mosses and liver- worts often have the sexes separate and very unlike. Nature furnishes, indeed, hundreds and thousands of instances of inde- pendently acquired sexual diversity without use either in environ- mental relations or in reproductive processes. The use lies, we may believe, not in the particular differences but in the diversity of descent which the species is enabled to maintain. Diversity is of value to a species not only to enable it to exist under a variety of conditions, but also because diver- sity in descent is an important factor in maintaining the organic strength or vital efficiency of the individual organisms. We may still believe that all character differences have their uses, but the use is not confined to environmental or selective considerations. More fundamental than these is the use of the diversity to the organisms themselves. Sexual differences contribute, in other words, to the increased effectiveness of sexual reproduction, that is, they intensify the ASPECTS OF KINETIC EVOLUTION 249 effects of fertilization or cell-conjugation in endowing the new organism with the power of vigorous growth. With this inter- pretation of sexual differences in mind we are the more ready to entertain the idea that specializations of heterism would be beneficial, even apart from the sexual diversification of the species, and are thus able to recognize and appreciate a group of phenomena which has hitherto remained meaningless and neglected. Since the time of Sprengel and especially since Darwin, it has been known that many plants, even those which are bisexual, or provided with both pollen and egg-cells, have many specialized habits and devices which serve to secure cross-fer- tilization. Although possessed of pollen of their own the flowers are often so formed that the pistils receive pollen only from abroad, and in many species foreign pollen is a necessity, pollen from the same plant being entirely ineffective. The advantage of cross-fertilization being admitted, the value of these adapta- tions for securing it becomes obvious, but the benefits lie, as Darwin discovered, not in the " crossing by itself" which " does no good," but in the diversity of parentage which may in this way be brought about. These specializations have, in other words, a double function ; they assist in the crossing and also minister to the diversity of descent which is the object of the crossing. They have, in other words, the same function as sexuality, and have been interpreted by naturalists as a simple or incipient form of sexuality. Still simpler specializations of heterism have only one of these two functions, that of maintaining the diversity, but without assisting in the bringing of the diverse parents together. The crossing is left, apparently, to chance, but when it takes place the diversity renders it the more effective. As instances of this simple type of specialized heterism may be cited such species as Verbascum blattaria, the flowers of which are pink on some plants and yellow on others. The two types grow freely inter- mingled over wide ranges of country but no intermediates are found. 25O COOK DIFFERENCES OF ADJUSTMENT TO ENVIRONMENT (ARTISM). The notion that all of the differences to be found among the individual members of species are caused by inequalities of en- vironmental experience finds no warrant in the vast mass of experimental facts accumulated by agricultural experience with domesticated plants and animals, nor in observations of species in undisturbed natural conditions. The differences which can be ascribed directly to environmental influences are relatively few and of little importance for evolutionary purposes. Of in- direct effects of environment there are two principal classes, those which arise from the ability of organisms to adjust or accommodate themselves to different environments, and those which result from a disturbance of heredity by new and unac- customed conditions. The individual members of species often differ among them- selves as a result of the possession of a certain range of organic elasticity or power of adjustment to different environmental con- ditions. Such differences are commonly greater among plants than among animals, for the latter are often able, through the power of locomotion, to choose or to control the conditions under which they shall exist, while stationary plants are sub- ject to much wider ranges of environmental vicissitudes. It has often been taken for granted that these differences of accommo- dation are direct results of environmental influences, the or- ganism being thought of as having a merely passive plasticity. The fact is, however, that this power of accommodation is as positive a phenomenon, as truly a form of organic activity, as growth, locomotion or reproduction, and as worthy of a definite and appropriate designation in evolutionary literature. Indeed it is no mere figure of speech to term these differences accommodations. The word can be used of plants and animals in their environmental relations in quite the same sense as for the change of convexity executed by the human eye to enable objects to be clearly seen at shorter or longer distances. This group of intraspecific differences has received a large amount of study from evolutionary specialists, and especially from ecologists and others who hoped to find the causes of evo- ASPECTS OF KINETIC EVOLUTION 2$l lutionary progress in mechanical effects of environmental influ- ences. A large number of special phenomena of artism have been named, such as heliotropism, or the power of plants to grow toward the light or to turn themselves to face the sun. Ge- otopism is the opposite tendency of the roots to bury themselves in the soil. Some writers on " evolutionary mechanics" have gone so far as to name the tendency of birds to stand or fly facing the wind as pneumotropism, and of fish to head up stream as rheo- tropism. Consistent prosecution of this tendency to ascribe special " forces," and to give technical names to each habit or instinctive act could result only in confusion, worse, indeed, than the older practice of ascribing all unexplained organic phe- nomena to a general "vital force." Even the operations of agriculture are conducted by many primitive peoples on an in- stinctive rather than a rational basis. In spite of permanent employment and a fully assured supply of food, the Indians of Central America obey an internal compulsion to scatter upon the land, when the proper season comes, to clear and plant their corn fields. Owners of mines and plantations have reconciled themselves to a complete suspension of work during the corn- planting weeks, having learned by experience that it is useless to oppose or to reason with this irresistible agricultural impulse. It would be possible, of course, to describe this agricultural instinct as a form of geotropism, a turning to the land for food as the root turns to the soil. The practical point is not, how- ever, the choice or application of terms, but to note the prob- ability that the instinctive actions by which man and the higher animals adapt themselves to environmental needs belong to the same general class of phenomena as the accommodative changes of plants. We know why we clear the land and plant our crops, and if the need or the advantage be not present we have no difficulty in discontinuing our agricultural labors, but it is not likely that agriculture arose, in the first place, as a conscious and deliberate art. Its beginnings are probably to be traced back by imperceptible stages to the primitive root crops of trop- ical America which grow readily from cuttings of the stems and rootstocks, so that the digging and harvesting of one crop plants and cultivates the next. 252 COOK We permit ourselves to say that agriculture was learned in some such accidental way, but we forbear to say that plants also learn to adapt themselves to take better and better advan- tage of environmental requirements. We base the distinction on the fact that we have reasons for our actions, but in the great majority of comparable cases the reasons have been discovered long after the arts had been perfected. We have theories of swimming, but young children often swim quite as instinctively as animals. This may appear an entirely irrelevant digression, but a use- ful purpose may have been served if we are ready to recognize the essential unity of the phenomena of accommodation or direct adaptation and cease to demand special explanatory terms and hypothetical forces for each of the multifarious forms of adap- tive change. The explanation will come when our knowledge of protoplasmic organization has sufficiently increased, but in the meantime we gain nothing by multiplying the mystery or by giving it a multitude of names. Under the theory that environment causes evolution a very real and important relation was supposed to exist between artisms, or adaptive alternative characters inside species, and ecology, or the study of the adaptive characters of species. Artisms or environmental adjustment variations have received much consideration from those who have held that evolution is caused by the environment, and who have believed, in accord- ance with this view, that the environmental variations were true examples of progressive evolutionary change, carried forward by external influences. This doctrine became untenable when Weismann showed that characters directly " acquired" from the environment are not inherited, that is, they do not show any tendency to repeat them- selves unless the inducing conditions are present. Weismann proposed to explain the possession by the same species of alter- native characters by his theory of determinants, or internal " mechanisms of heredity." These determinants were thought to control in advance the characters of the organism, and alter- native characters were explained as the work of two or more sets of determinants which could be brought into action by par- ASPECTS OF KINETIC EVOLUTION 253 ticular conditions. Where the alternatives are sharply defined as in the two sexes of man and the higher animals this theory might appear to be applicable, but where, as in many plants, there are, even in the same species, all stages of sexual differ- entiation, or many distinct castes or forms, with or without reference to the sexes, the theory of determinants becomes im- practicably complex. In the experiments of Standfuss with butterflies it has been found possible, by changes in the temperatures in which the pupae are kept, to influence the colors of the adults so as to approximate those of a different geographical variety or seasonal form. It has been inferred as a consequence that temperature is a direct evolutionary factor in causing one species to change into another. In reality, however, this is but one of the many instances in which failure to distinguish between the taxonomic and the evolutionary standpoints has permitted confusion to enter. Some of these seasonal and geographical forms of but- terflies have been named as distinct species, but if it be found that the supposedly distinctive characters are merely artisms or accommodations to temperature, the proper step is to revise our classification before attempting to use it as a basis of evolu- tionary inferences. The largest possibility suggested in the present instance is that abnormal temperatures may induce in one part of a species a character which another part has reached by normal evolutionary process. The fact that the different geo- graphical color races may have been described and named as species and varieties cannot be made to prove that temperature is a cause of species-formation. This power of accommodation to the environment, specific elasticity or artism, may be thought of for evolutionary purposes as a general character of the species, but like other characters it is possessed in different degrees by different individuals, and this difference of degree is as heritable as any other feature. Some individuals and strains of a species may have greater range of elasticity on both ends of the series, while others have greater freedom of change in one direction than in the other, for example, they can become very hairy, but not very smooth. Still again, we find mutative variations toward a restriction of the normal 254 COOK range of development. Some of the coffee mutants have ex- tremely short internodes. None of these complications need obscure the fact that the phenomena of artism can be viewed as entirely distinct from those of heterism, though neither phe- nomenon excludes the other. DIFFERENCES OF USE AND DISUSE. One of the reasons for the persistence of the belief that adjustments to external conditions represent direct effects of environment, lies in the fact that several other kinds of intra- specific differences have been confused with environmental adjustments. Most of these additional types of diversity are rather uncommon, but they are well calculated to confuse thought and even to vitiate experiments, especially when these are undertaken without fully considering all the sources of possible error. If an animal or a plant be kept in captivity or placed other- wise under conditions where its normal activities are not called into use, muscles or other organs may fail to reach their normal development, or they may actually decline in size and deteriorate in structure under continued disuse. There are certain senses, of course, in which it may be said that the environment, by determining the use of parts, causes them to prosper or decline, but closer attention will show that these are phenomena of growth and nutrition rather than of environmental adjustment. The use of a muscle is as truly a condition of its development as the food from which the tissue is nourished, and the decline of such a part may be reckoned as a starvation phenomenon, or interference with the normal processes of growth. The fact that so much has to be learned through precept and practice by the young of the human species has led some to overlook the existence of definite instincts and muscles which develop without use, just as the internal organs and functions develop in the embryo before birth. The idea that there is a natural and general tendency to evolutionary motion, to change of organic form and structure, need not be confused with the predication of a principle of evo- lutionary perfection by which some writers have thought that ASPECTS OF KINETIC EVOLUTION 255 organisms might be carried along in an ever-upward direction. Some species have gone forward or upward, but for each of the groups which has been able to perpetuate itself by continuing upward there have been hundreds and thousands which have not continued in lines of effective progress, but have turned aside and have been extinguished. This is as true of man and of human societies as of species. They do not tend to go upward but they do tend to change and these changes have carried a few upward to higher levels, where new planes of development and expansion were possible, but where the prob- abilities of still further steps were as doubtful as before, and as truly dependent upon correct, if unconscious choice. One view is teleological, the other purely causational. The phenomenon of degeneration, the reduction or elimination of unused parts or organs, has led to the placing of undue emphasis upon the utilitarian aspect of evolution. Darwin attempted to connect the deficient size and strength of the unused organs of the individual with their reduction in the species by means of his theory of pangenesis which assumed that all parts of the body contribute to the reproductive cells. Degeneration was made a converse of natural selection ; the reduction was believed to appear first in the adult, and then the negative acquired character was transmitted to the next generation. Many characters of adult organisms consist in part of a genetic or hereditary contribution, which might be called a qualitative element, to which is added during growth a quantitative reaction to more or less favorable conditions, depending not only upon external circumstances but also upon the perfection and effi- ciency of the remainder of the organism. Disuse undoubtedly affects the quantitative side of the development of voluntary muscles and other analogous organs, but it is not easy to under- stand how a progressive reduction could be brought about on Darwin's hypothesis. After the elimination of the quantitative element due to use, a state of stability might be expected to ensue, unless there be predicated in addition a principle of organic economy tending to the gradual and continued elimination of useless characters and organs. In other words, the effect of pangenesis acting 256 COOK alone would be limited to comparatively few generations, and would dispose of superficial and recently acquired characters only, an inference apparently supported by the persistence of many rudimentary organs. The extreme constancy of vestigial characters confirms the a ■priori expectation that selection would have little to do with them except to eliminate ; but differences, nevertheless, occur, of which progressive modification without selective influence must necessarily be predicated. Weismann's panmixia was intended to represent a view diametrically opposite to that of Darwin, approaching the question of reduction from the side of heredity only, and laid emphasis on the opinion that, selection being discontinued, indis- criminate crossing without reference to the character previously at a premium would result ultimately in the reduction of the selectively developed parts. But even if it be admitted that a reduced average would be attained within specific limits or where intercrossing is possible, panmixia remains entirely inad- equate to explain the progressive elimination of wings, legs, eyes or other important parts of the body, unless it be extended, as in the previous case, to an organic law of economy, a prop- osition logically quite distinct from panmixia. It is of inci- dental interest to note that both Darwin and Weismann have thus tacitly admitted a law of organic motion in the direction of the simplification of organisms, and that this proposition is again the exact opposite of that of Nageli whose " Vervollkommungs- jirincij)'''' works from the simple to the complex. The phenomena of degeneration may appear to militate against the idea of a spontaneous organic motion. The belief has been that though organisms are in a sense elastic, in that one or more characters can be far drawn out by selection, they tend more or less promptly to return to what might be viewed as the previous condition of rest or equilibrium. Especially would this be the case where selection has been very acute and has accen- tuated one character at the expense of the total efficiency of the organism with reference to conditions other than that which has determined the special selection. The removal of the latter would then involve the loss of the advantage gained by selec- ASPECTS OF KINETIC EVOLUTION 257 tive response to the special demands. In groups subjected to an active struggle for existence this would mean a change of direction rather than a cessation of selection. In many other instances, notably among parasitic forms, the loss of normal organs ascribed to disuse is better explainable by selection, since the apparent degeneration is of decided advantage from the standpoint of the actual life-history of the animals. The principle of panmixia seems, indeed, to involve an un- warrantable extension of the idea of organic elasticity, since it implies that organic structure is maintained by selection alone, without which everything would drop back to simple protoplasm. Of such a general tendency to degeneration there is, however, no indication. As explained elsewhere, the reversion of inbred highly selected types to the wild form of the species is not de- generation, but a recovery of normal structure after restoration to normal conditions of interbreeding. DIFFERENCES OF DEFICIENT ACCOMMODATION (TOPISM). Environmental differences are not all of one kind. Some of them are the results of the power of accommodation or adjust- ment (artism), while others represent rather a deficiency in ability of this kind, so that the organism, though perhaps able to maintain an existence, fails to attain one or another of the normal characters of the species. Thus there is a variety of canary bird which if fed on cayenne pepper during its period of moulting produces red feathers instead of yellow. The South American Indians are said to be able to alter the color of the feathers of their domesticated parrots by inoculating them with the blood of toads. The colors of certain flowers can be modified by special conditions or by treatment with chemicals. The injury of the white pigs from paint-root, while black pigs escaped, as related by Darwin, would be another example of the same group of phenomena. The relations of topism to artism and to teratism are some- times very intimate. A character assumed by one plant as a means of accommodation may appear in another as a limitation of the power of accommodation or as a complete abnormality. The need of discrimination and the difficulty of exercising it 2 58 COOK are frequently apparent in the literature of the subject. Thus it has been inferred from experiments on a spiny New Zealand plant that the spines, instead of being a means of protection against grazing animals, of which there were none in New Zealand, are in reality an adaptation against transpiration, because they do not appear when the plants are cultivated in a humid atmosphere. "After being placed in the moist chamber, the plants devel- oped no more spines and are now seedling plants in all respects except for the few spines, which were developed prior to the culture in moist air. Moreover, it seems evident that such plants would remain in the seedling form so long as they were kept in an atmosphere constantly moist and exposed to a feeble light. " Even an adult shoot on a full grown plant in the open and freely producing spines, may have any further production of such suppressed at once, if the shoot should continue its growth under slightly more hygrophytic conditions. Thus quite recently, I observed on the clay hills near Wellington, a shoot creeping near the ground whose apical portion was covered by grass. This shoot where fully exposed to the light was spinous as usual, but where shaded and in a slightly moister atmosphere was quite without spines. " From the above it follows that the production of spines in Discaria Toumatou can be controlled at will by specifically changing its environment — a plant exposed to a dry atmosphere and normal light producing spines, whilst one exposed to a moist atmosphere and a feeble light produces no spines, but in their place leafy shoots of unlimited growth. " That spines on xerophytic plants are an adaptation against the attacks of grazing animals is a matter of such general belief as to be admitted into certain botanical text-books as a proved fact. " It seems, however, to me that my experiment, detailed above, is a fairly crucial case, and that in Discaria Toumatou, at any rate, the spines are a direct response to conditions of dryness, and function as a special contrivance for checking transpiration. If so, then they have nothing to do primarily with attacks of ASPECTS OF KINETIC EVOLUTION 259 grazing animals, especially when it is borne in mind that New Zealand never contained such, excepting the various species of Mo a."1 That the spines did not develop under conditions of moisture and feeble light can scarcely be accepted, however, as proving that they are a special contrivance for checking transpiration, for many analogous adaptations do not fail to appear in advance of the conditions which require them. Cacti, and other spiny plants often make most of their growth in periods of humid weather, but they do not on that account fail to put on spines. The possibility that the spines may be a useful form of tissue for the plant when living in the normal desert habitat is not a sufficient explanation of the failure to produce the spines under conditions of humidity and deficient sunlight. The spines might be an adaptive character and still appear under all conditions of growth. They might represent an adjustment character or artism and still be only reduced instead of being eliminated in the shade form. That the spines disappear entirely indicates that another factor may need to be recognized, that certain conditions are necessary for their development, and that without these condi- tions the plant is unable to make spines, just as the pepper-fed canary birds may be thought of as no longer able to produce yellow feathers. The interest of the Discaria experiment would have been increased if it had included a test of the behavior of the plants in shade conditions without excessive atmospheric moisture, to determine whether deficiency of light might not of itself inhibit the formation of the spines, simply by restricting the activity of the cells. The formation of the spines is a specialization which the seedling plants do not attain until they have grown to con- siderable size, perhaps not until they have encountered condi- tions of drought and exposure to strong sunlight. It is, there- fore, not unreasonable to suppose that these conditions are a necessity to enable the plant to produce the spines, and hence that its failure to produce them represents not so much an accom- modation as a lack of accommodation, that is, topism, instead of artism. 1 Cockayne, L., 1905. Significance of Spines in Discaria Toumatou Raoul (Rhamnaceas), New Phjtologist, 4 : 79. 26o COOK The prompt loss of wool by sheep brought to tropical coun- tries is one of the most striking instances of response to environ- mental conditions, but there are several elements which need to be taken into account in attempting to arrive at a clear under- standing of the nature of the process. The continuous heat and excessive humidity may induce an abnormal condition of the skin and cause the hair to fall out, as often happens in hu- man fever-patients. On the other hand, the failure of the sheep raised in the tropics to produce wool may be due to a lack of sufficiently normal conditions of existence which disturbs the normal heredity and affects first the most highly specialized character of the animal. The loss of wool could be explained in this way as a deterioration or reversion rather than as a new or adaptive character. The domestic sheep is now supposed by Lydekker to be descended from wild types which had a hairy summer coat and produced wool only as cold weather approached.1 Many animals and plants require the seasonal vicissitudes of heat and cold as a normal part of the conditions of existence, and refuse to behave normally in tropical regions where wide ranges of temperature do not occur.2 Indeed, the changes of temperature appear to supply to some of them the same kind of bodily vigor to which diversity of descent contributes. The plants and animals of. tropical regions appear to have rela- tively great rapidity of evolutionary progress, as pointed out by President Jordan, who finds that the tropical fishes are much more highly specialized than those of extratropical waters. "The processes of specific change, through natural selection or other causes, if other causes exist, take place most rapidly there and produce most far-reaching modifications."3 It has not been shown, however, that natural selection is less acute in the colder regions of the globe ; in fact, the general impression has been that the requirements are the more stringent and exacting. 'Lydekker, R., 1904. The Field, 104: 654. 2 Apples, cherries and many other temperate trees and cultivated plants fail to reach productive maturity under consistently tropical conditions, just as the seeds of lettuce may refuse to sprout without alternations of temperature, and the eggs of some mosquitoes refuse to hatch unless they have been frozen. 3Jordan, D. S., 1901. Science, N. S., 14: 566. ASPECTS OF KINETIC EVOLUTION 26 1 TEMPORARY EFFECTS OF NEW CONDITIONS (NEOTOPISM). Experiments to test the effects of different environments upon plants are often interfered with by a temporary stimulation of growth, due, apparently, to the fact that the conditions are new, rather than to any essential superiority of the new place. Like travelers in foreign countries they may often behave in a manner very different from their habits at home. Organisms, as well as men, though not built by their environments, are often built into them to such a degree that where the accustomed supports and restrictions are taken away the usual courses of action are no longer followed. New and unexpected character- istics assert themselves, not only or chiefly because the new conditions cause the organism to vary, but because they give it an opportunity to do so, or strengthen and bring to expression some tendency or instability of equilibrium. The new characteristics which have a definite connection with the new environment and are in the nature of adjustments to it may be expected to continue, but there is, in addition, a temporary effect, a temporary lack of adjustment, or a stimulation or aberration which sooner or later disappears. This phenomenon may be called neotopism, or the new place effect. It is often strikingly shown in plants, and is not lack- ing in animals. The most familiar example of it is, perhaps, that of the tonic medicines. A vast number of substances, utterly unlike among themselves and having utterly diverse specific actions upon the human system when taken in large quantity, may nevertheless produce the same beneficial effect of temporarily increasing the efficiency of the organism, when taken in extremely small doses. Neotopism is also to be reckoned as one of the factors con- tributing to the great vigor and rapid distribution of plants and animals immediately following their introduction into a new region. It is true that they may also have the advantage of immunity from diseases or natural enemies to which they were subject at home, but this is by no means a sufficient explanation of the unusual vigor and fecundity which they manifest for a time and which disappears after a series of years. Many plants, like the Russian thistle, which terrified the agricultural regions 262 COOK of the Middle West a decade ago, after threatening for a time to become permanently injurious pests, have taken their places as comparatively peaceful settlers among the older plant inhabitants. Neotopism is a phenomenon long known in practical agricul- ture, but hitherto not explained and generally not accepted in the scientific world, because the requisite evolutionary viewpoint was lacking. Having come to appreciate the physiological functions of heterism in maintaining the vital efficiency of organ- isms, we are in position to understand that a transfer to new conditions may also act as a direct stimulant of organic vigor, an artificial symbasis, as it were, which has probably contrib- uted much to the sustained vitality of our inbred cultivated plants. Likewise the heterism of the species might be thought of as increased by the extension to the new locality, and the added neotopic diversity might serve the same purpose as normal heterism in helping to maintain the organic vigor of the species as a whole, under conditions of free interbreeding. Thus devices for securing wide distribution serve the interests of the species in a variety of ways. They not only tend to increase the numerical prosperity of the group, but increase the facilities for interbreeding among the members of the species and also give it the benefit of as widely different conditions as possible. The diversity of conditions accentuates diversity of descent and thus contributes to the vigor of the species. With sedentary plants in particular we should be prepared to learn that changes of conditions of growth are as beneficial as changes of diet for man and the higher animals. In many crops it has become a regular agricultural practice to exchange seed between more or less distant localities. Seed planted in a new locality often produces better and more fertile plants than in the place where it was grown, and better than the same stock after it has been planted in the same place for a series of years. The new conditions afford, for a time, the same physiological benefits as diversity of descent and new variations, and constitute, indeed, a striking confirmation of the physiological relations of these groups of phenomena. In many other cases neotopism may only bring to the surface ASPECTS OF KINETIC EVOLUTION 263 and accentuate conditions of degeneration. Many varieties of domesticated plants and animals have been bred so long and so narrowly in one particular locality that any change is accom- panied by notable deterioration. Thus it comes to be believed that seeds of one particular plant, such as the radish or the cauliflower, can be grown to perfection only at Erfurt. Trans- ferred to any other point, neotopic mutation at once appears and brings diversity and commercial inferiority. In a similar way many high-bred animals like the Jersey cattle also deteriorate or show special susceptibility to disease when subjected to new conditions, even to those in which other less closely adjusted breeds are able to thrive. BEARING OF NEOTOPISM UPON ACCLIMATIZATION. Neotopism must also be taken into account in another depart- ment of agricultural investigation. The phenomenon is often very marked in plants introduced from tropical countries into tem- perate regions, and has had the opposite effect of deceiving us regarding the possibility of acclimatizing species or varieties of tropical origin. The popular impression is that the colder climate of our more northern latitudes will restrict the growth of plants from the tropics, but this is the reverse of what usually happens, as a matter of fact. It seems to be a general law that annual-crop plants, whether of temperate or of tropical origin, are most vigorous and productive near their northern limit of growth. The reason for this is that the longer days supply a greater amount of heat and sunlight than in the tropics themselves. Plants newly introduced from the tropics commonly misuse these exceptionally favorable conditions to put forth an abnor- mal amount of vegetative growth and are often killed by frost before they commence fruiting. It has been usual to explain the failure of such experiments on the simple ground that our northern season has proved too short for these tropical varieties, but as a matter of fact the time may have been equal to that required by these same varieties for normal growth and maturity at home in the tropics. Thus the Kekchi variety of Upland cotton, which matures seeds in Eastern Guatemala in five months from planting, required in Texas over six months to produce Proc. Wash. Acad. Sci., January, 1907. 264 COOK a much smaller crop the first year after its introduction, and might have produced no seed at all if the tendency to abnormal luxuriance of growth had not been checked by a long period of dry weather. Other tropical varieties of cotton have consistently refused to produce seed when introduced into Texas, even though the same length of season would have been sufficient in their home localities. With the superior conditions of growth supplied by our north- ern summers most of the tropical varieties would be able, if they utilized their opportunities properly, to develop even more rapidly than they do in the tropics, and this result has been reached with some of the Mexican varieties of corn. During their first seasons in the United States they became greatly overgrown and ripened scarcely any seed, but after a few years they recovered their short-season qualities and became es- pecially useful as extra-early varieties, like the " Mexican June" corn. The conditions under which such experiments are usually made are well calculated to intensify neotopism instead of hold- ing it in check. It has been reasoned after the analogy of our domestic varieties that fertile soil and thorough cultivation will conduce to the early maturity so much desired. Moreover, it is the regular practice to keep testing gardens and experimental plots in the best of condition. The result is that the newly in- troduced tropical variety is surfeited with the unwonted supply of readily available food and moisture, which still further in- creases the tendency to abnormal vegetative growth. Many such varieties have entirely failed of acclimatization because they ripened no seed at all in the localities in which the first experiment happened to have been made. Neverthe- less, the inference is not warranted that such varieties cannot be acclimatized in temperate regions. Experiments in the in- troduction of new types of Upland cotton from Guatemala have shown that the tendency to rank and sterile vegetative develop- ment can be controlled by carrying the new stock far enough to the north and placing it in comparatively sterile soil. In the latitude of Washington the Guatemalan varieties of cotton showed much more normal habits of growth, and made more ASPECTS OF KINETIC EVOLUTION 265 progress toward fertility and seed-production than in the much longer growing season of Texas. These experiments afford a definite intimation, to say the least, that by the proper choice of conditions for the first planting the neotopic stimulation of trop- ical varieties can be held sufficiently in check to permit the ma- turing of at least small amounts of seed. This opens the way to the practical acclimatization in the United States of useful varieties of cotton, corn and other important food-plants of tropical origin. Further experiments have shown that the second generation of cotton in the United States is notably earlier and more productive than the first generation, when grown from seed of the same origin and planted in adjacent rows. It has also become evident that there are at least three stages or kinds of new place effects to be considered in the acclimatization of different varieties and types of cotton. The changes of hered- itary behavior which can be induced by the transfer to new conditions are not limited merely to increased size or vigor, but have obvious bearing upon the phenomena of mutation, since the plants may change in a very definite manner in characters which would usually be considered of varietal or even of specific importance. The lack of fertility which accompanies the aber- ration from normal characters affords a further analogy with mutations. Nor does the interest of the experiment end here, for it has been proved that this neotopic form of mutation may supervene in a perfectly definite manner even after the plants have grown for a time according to the specifications of normal form and habits of the variety. When the change takes place early the whole plant may show the abnormal characters and may be more or less completely sterile. In another locality plants of the same origin may grow for a time in a normal manner and remain normally productive, but may then change suddenly and completely to the abnormal, infertile, neotopic condition. In this form of neotopism the behavior of the individual plants grown from the same lot of imported seed is often remarkably uniform and the result is closely parallel to that described a few years ago by Dr. C. A. White in tomatoes. Two lots of seed produced, with much 266 COOK uniformity, progeny so unlike their parents that Dr. White described and named them as a new species.1 A third result sometimes reached by transferring plants to new conditions is to induce a more or less general outbreak of miscellaneous variations of an abruptly mutative character. In such instances the stimulation effect may be lacking or very inconstant. Some individuals may be several times as large as their parents, while others are as much smaller. Although the new conditions evidently induce the mutative variations, they can not be said to cause them, in any definite evolutionary sense, as proved by the great diversity of the muta- tions which the same change of conditions may call forth. The unfavorable conditions unbalance the organisms, but the indi- vidual lapses from normal heredity take many different direc- tions, without reference to particular requirements of the environment. The practical significance of the new-place-effects is, there- fore, entirely different in different instances. As long as the result is an increase of vigor and fertility, the phenomenon is a useful one ; but if the stimulation be so great as to change the characters of the plants and render them infertile the crop may be ruined, and this misfortune may also be reached when many miscellaneous variations and degenerations appear. DIFFERENCES ARISING FROM PARTIAL ISOLATION (PORRISM). Members of the same species are often more or less unlike in the different parts of their geographical range of distribution. Some of these differences will be found to have relations to differences of environment, but others will persist even when brought into tne same conditions. These geographical diversi- ties represent, no doubt, the results of partial isolation, and are of the same nature as the differences between species. If inter- breeding were adequate, evolutionary progress would be kept uniform over the whole species, but if the organism is sedentary or lacking in facilities of dispersion local diversities may accu- mulate. 1 White, C. A., 1905. The Mutations of Lycopersicum, Popular Science Monthly, 47 : 151. ASPECTS OF KINETIC EVOLUTION 267 Individuals from neighboring localities may maintain the usual amount of similarity, but if specimens from remote parts of the geographic range of the species be compared they may prove notably different. If the climatic or other conditions of the two localities are unlike it is very natural to infer that this is the cause of the differences between their organic inhabitants.1 That this explanation may prove, in some cases, to be correct, does not justify us, however, in neglecting to perceive that the remote members of a species may have opportunities to accu- mulate diverse characteristics, much as though they belonged to two distinct species. The extent to which they can do this will depend upon the habits of the particular plant or animal. Sedentary species of animals or plants which have no means of securing wide dissemination of seeds or pollen, tend to manifest local divergencies. The cause of this is, apparently, that new characteristics appear in different parts of the range of the species more rapidly than they can be distributed through the whole interbreeding group. Thus the quail, or Virginia par- tridge, a nonmigratory bird extending from New England to Central America, shows a large number of appreciably different local varieties or subspecies, which might not exist if the bird were migatory and there were a more general intermingling of the members of the species. The differences which charac- terize such local subspecies may be quite the same, both in character and amount, as those which distinguish completely segregated species, but they are treated as subspecies because the distribution of the whole group still remains continuous, and provides a complete series of connecting links between the local forms which happen to be described as subspecies. 1 Engler, A., 1904. Plants of the Northern Temperate Zone in their Transi- tion to the High Mountains of Tropical Africa. Annals of Botany, iS : 539. " I am convinced that in such cases the somewhat different climate is the cause of all or at least of a part of the modifications. Sometimes in connection with these new variations are also to be observed (cf. Cerastium ccespitosum), which may become the beginning of other new forms. The constancv of such climatical adaptations may be a different one and often become fixed through a geological period. I may add that systematic studies have also convinced me that many of the xerophytes, and that a good deal (I do not say all) of the quali- ties of xerophytes, which are usually called adaptations for protection against a dry climate, are caused by the climate itself." 268 COOK The essential difference between a species and a subspecies does not lie, as commonly supposed, in the nature or amount of the differences as such. The practical question is whether two groups are actually separate in nature or are still connected. Subspecies may be more different than other completely segre- gated species. On the other hand, groups which are really segregated in nature and thus unable to interbreed, are by that fact on the road to the acquisition of specific differences. That they may not have become very different from each other does not prove that they are not good species or that it is undesirable to accord them recognition as such. It does not follow, as some have supposed, that subspecies are always incipient species, or that there is any inherent force or tendency which will insure a subsequent separation into distinct species. The existence of these diverse local forms has not been shown to be any disadvantage to a species, and may, indeed, conduce to its greater vigor, since it tends, like heterism, to insure a certain amount of desirable diversity of descent. If the habits of a species were to change in the direction of an increase of its power of dissemination and wide interbreed- ing, the local differences would tend to disappear, since new variations could then spread more rapidly throughout the whole group and render its evolutionary progress more uniform. Porrism corresponds, inside the species, to many of the dif- ferences between species. It is true that when species of the same genus live in different environments and have different habits they usually have structural difference corresponding to their respective needs. Examples of such adaptations are fre- quent among the higher plants and animals, and their super- ficial similarity to artism inside the species has been the basis of the doctrine that evolution has been effected by environmental causes. The best corrective of this misapprehension is a study of one of the lower groups of plants and animals in which the same family, order or class has the same habits and the same place in the economy of nature. Many excellent examples will be found among the mosses, liverworts and alga? among plants, and among the myriapoda and lower insects where the number and character of the diversity of the species is out of all imag- ASPECTS OF KINETIC EVOLUTION 269 inable proportion with differences of conditions, habits or selec- tive requirements. Hundreds of species, genera, families, and even orders, have been differentiated notwithstanding complete and long-standing adjustment to the same kind of existence. The multiplication of species under such circumstances has little reference to environment or to natural selection, and the characters by which the groups differ are not explainable on the basis of utility. The diplopod fauna of tropical Africa changes almost completely every thousand miles, but the tropical forest conditions under which a large proportion of the species live are, for their purposes, practically identical the world over. But with these wingless, slow-moving creatures unable to bear exposure to daylight and dry atmosphere, the opportunities for segregation are greater than those for dissemination. The environment allows a wide freedom of choice, and evolution by means of useless changes has far outrun the natural selection of advantageous differences. As far as their external charac- ters are concerned, these animals appear to have been quite as well adapted to their environment in the carboniferous age as they are to-day, but they have not ceased to differentiate species, although preserving much more than in some groups the same general form. Indeed, the wealth of definite structural differ- ences is, if anything, greater than among the higher insects, where the progress in adaptive structural changes would seem to have removed the necessity of accentuating the inconse- quential differences which the diplopoda have utilized as means of evolutionary motion. DIFFERENCES OF NEW VARIATIONS (NEISM). Much of the heterism or normal individual diversity of the members of a species can be described as resulting from differ- ent combinations and proportions of what have been called the unit characters of the species. The interweaving of the lines of individual descent brings, as we know, an infinite diversity of form and features, and with these differences accentuated by environmental influences there is almost an infinity of possibili- ties of diversified characters in the same species. Nevertheless, the making of all possible permutations of the characters which 27O COOK may exist in a species at any particular period would lead, after all, to no truly progressive change. Nothing is gained for evo- lutionary purposes by attempting to explain new characters merely as reversions or as new combinations. Nor can such assumptions fully account for the facts, since it is often obvious that absolutely new and unprecedented evo- lutionary departures sometimes appear, which could not be accounted for by any combination of characters existing in the remaining members of the group. Such are the remarkable crests developed on a few of the anterior segments of East African millipedes of the family Oxydesmidae, specialized structures which are entirely without analogy in the remainder of the order Merocheta or, for that matter, of the entire class Diplopoda. It would be altogether presumptuous, of course, to insist that any particular variation or mutation represented the very first appearance of its type in the history of the species. It is usual to ascribe variations to possible admixtures of blood at some point in the genealogy of the individual, near or remote. But these suggestions, even if justified for particular cases, should not be allowed to obscure the more fundamental consideration that the very idea of a progressive evolution implies the origina- tion and development of new characters, both of form and of structure, and the opening of new environmental relations for the species. Of the causes of new characters we are, as yet, in ignorance, but of their uses we need be in no doubt. New characters not only make evolution possible, but by true symbasic interbreed- ing they help to maintain the vitality or organic efficiency of the species. Neism reinforces heterism and contributes to evolu- tionary progress. New characters are not averaged away and obliterated by interbreeding, but are prepotent. They tend to spread throughout the species and to become more and more accentuated. That variation may bring an increase of the vegetative vigor or vital efficiency of the organism could not be more clearly shown than in the numerous instances where unusual bodily strength and hardiness accompany reproductive debility or even ASPECTS OF KINETIC EVOLUTION 27 1 complete sterility, as in the familiar instance of the mule.1 Many similar instances were observed in Guatemala. Coffee plantations which, owing to unfavorable conditions, were dead or dying, often showed occasional mutations which remained healthy and luxuriant. Through some strange internal differ- ence they were able to carry on their vital functions with con- spicuous success while all their normal neighbors had completely failed. If coffee were grown for the leaves like tea or for other vegetative parts, these mutations would furnish new types of great economic value, but of thousands of such variants which have come under the observation of planters not one has proved to be equal in fertility or normal seed production to the parent type, under favorable conditions. PREPOTENCY OF NEW VARIATIONS. If only a small proportion of the progeny showed the new character it might still gain a footing in the species, especially if favored by selection. Those who have relied on the mathe- matical doctrine of chance have felt it necessary to claim gen- erous assistance from the principle of selection. Experiments with new variations seem all to agree, however, that among their own relatives, or under equal conditions of symbasis, they have not merely an equal chance of reproducing themselves, but that probabilities are distinctly in their favor. The variation is not resisted but welcomed. The majority does not set the fashion ; it is the few who are able to make pleasing modifica- tions of style. The new pattern may not be better or more beautiful than the old, but change is pleasing in itself and may secure a wide vogue for an ugly or uncomfortable garment. With organisms as with clothes the essence of beauty is fitness, as Socrates long ago pointed out. The changes which make a permanent contribution to evolutionary progress are those which fit best into the existing structure and increase its fitness to its surroundings. Our admiration for changes and likewise for fitness in nature and in art, may be an intellectual reflection of the evolutionary properties of organisms. 1 Cook, O. F., 1904. The Vegetative Vigor of Hybrids and Mutations. Proc. of Biological Society of Washington, 17: 83. 272 COOK DIFFERENCES OF ABERRANT HEREDITY (TERATISM). There are many biological accidents, so to speak, as when in the laboratory, or perhaps in the surf of the sea beach, an egg of one of the simpler animals is shaken apart and develops into two organisms instead of one. In a similar manner, through some mistake of division, two-headed monsters and other mal- formations occur. No less abnormal are many of the freaks which can be produced by unfavorable conditions of growth. Another series of abnormalities is caused by violations of the law of symbasis, that is, through inbreeding which eliminates heterism and normal diversity of descent. Teratic characters which are the result of accidents of growth or environment are not inherited, except as they may give rise to a general weakness or debility of the organism. Teratic neisms, on the other hand, are readily heritable. Teratisms, like accommodational variations, have received much study, especially from those who hoped to gain from organic derangements an insight into the nature of the agencies by which organic structures are built. The field of teratology affords many interesting and significant data, but the correct interpretation of them has been hindered, as in other departments of evolution, by the confusion of issues which are essentially distinct. There are at least as many kinds of teratisms as there are of normal differences, and probably more, and endless gradations of each kind. This is well illustrated by the phe- nomena of mutation which have received so large an amount of study in recent years. Mutations show all degrees of abnor- mality, and they grade imperceptibly into the differences of normal individual diversity (heterism) as well as into those of normal and prepotent new characters (neism). ABNORMAL MUTATIVE DIVERSITY. That species are not normally constant and stationary in their characters could not be better proved experimentally than by the many attempts of breeders of plants and animals to maintain constancy of characters in domesticated varieties. Selection conduces at first to such a constancy or uniformity among all ASPECTS OF KINETIC EVOLUTION 273 the members of the breed, those not conforming to the approved standard being ruthlessly weeded out. The type having been once established by this means, the variety remains for a period of years more or less uniform, generally very much more so than the members of wild species in nature. It is the experience of all history, however, that varieties decline after a time from their original excellence and have to be replaced by other, newer sorts, which by reason of their more recent origin have been subjected to shorter periods of inbreeding. The degeneration of the older variety may be indicated in a number of ways, such as a decline in fertility or weaker vegetative growth, or suscep- tibility to fungous and insect parasites, so that it usually dis- appears from cultivation or husbandry before the final stage of sterility and extinction is reached, though the tendency in this direction often becomes very obvious. One of the symptoms of degeneration is the appearance of numbers of freaks, sports or mutations, as they are variously called. These variations of domesticated plants and animals are often interesting, and sometimes valuable on account of some special peculiarity, such as long hair, double flowers, albino color, etc. This is especially true among the plants cultivated for their flowers, where the never-ending diversity of garden varieties is obtained by the preservation of the numerous mutations into which wild species commonly "break" after a period of domestication and inbreeding. A general tendency among all such sorts is towards lessening of seed production, and finally complete sterility may ensue. The last is not a calamity in species which can be propagated by cuttings, and many of our cultivated species have reached this condition. With others, as for example, the " seedless " green-house or forcing cucumbers, the extreme scarcity of seeds which renders the variety desirable is at the same time a serious obstacle to its cultivation. On the strength of the older static, uniformitarian theory of life, some writers have insisted that mutations must be caused by environment, there being, in their opinion, nothing else to cause them. The diversity of the mutations could be explained, under this doctrine, only by environmental differences, such as 274 COOK the variety of chemical compounds which might be found in the soil of the same seed-bed. But no evidence of any constant relation between any particular chemical and any particular mutative character has been adduced. That any will be forth- coming may well be doubted, in view of the fact that the same or closely similar mutative characters often appear under very different conditions of soil and climate, and very diverse muta- tions under the same conditions. The diversity of the mutations among themselves shows that it is not safe as yet to assert more than this general organic in- stability ; detailed causes are not yet revealed. The necessity of this caution is rendered still more obvious by the behavior of neotopic mutations, those induced by changes of environmental conditions. If in a given environment a plant mutated only in one direction, we would still be far from knowing adequately that the environment caused the mutation, but even when we have reason to believe that a change of environment has induced mutation we are forbidden to go farther, because of the very great diversity of the mutations which the same change of envi- ronment or the same history of selective inbreeding can induce. It has been shown in the discussion of neotopism that new conditions may conduce to the appearance of abruptly discon- tinuous mutative variations. The percentage of mutants is notably larger in some regions than in others, but even this does not compel us to believe that the conditions are the true cause of the mutations, in any detailed sense. They are rather to be thought of as merely the occasion of the change, by having brought the coffee, the cotton or the Capsicum the sooner to the point when it can no longer follow the hereditary road over which the individuals must travel to attain the ancestral type of adult form. The mutative individuals are not to be thought of as the evo- lutionary pioneers of the species ; they represent rather those who are falling out by the wayside. They may be classed to- gether with normal new variations in the sense that they are outside of the specific norm or average, but the)' have a dif- ferent position with reference to the evolutionary route of the species. They represent the criminals and cranks, but not the ASPECTS OF KINETIC EVOLUTION 275 leaders and reformers of the specific organization. For special agricultural purposes mutations are often extremely valuable, but when the desire is for the general improvement of the species or the race, the essentially degenerate nature of muta- tions cannot be left out of account. The kinetic theory, if correct, shows that variations, to be of evolutionary value, must take place in the species, or in full contact with society, as it were, and not alone, or in disregard of the condition, interests, and evolutionary direction of the species at large. Mutations are physiological phenomena, just as evolution itself is a physiological process ; they will undoubtedly be found to have causes when we are able to appreciate them. They may be thought of as functional reactions from the re- striction of normal heterism and diversity of descent. This ab- normal condition of inadequate symbasis renders the organism unstable and it falls down, degenerates or mutates. Inbreeding is to be studied as a condition of existence, and the manner in which the species reacts may be observed with the same propriety as any more purely environmental problem. Mutations may be abnormalities induced by abnormal conditions of descent, but the reaction which produces them need not be considered abnormal, since it is evidently the same tendency which contributes to the maintenance of the normal heterism. Indeed, the mutations might restore the normal intraspecific diversity if interbreeding were permitted, as in nature. The very fact that mutations of plants so frequently tend toward dioecism might be accepted as another evidence of their value as a corrective of inbreeding and deficient heterism. Coffee mutations are often largely or completely unisexual, or have greatly accentuated proterogyny or proterandry. A condi- tion entirely analogous to a dioecious species could be obtained by the crossing of such staminate and pistillate trees. Never- theless, Professor De Vries has described and named such a unisexual mutation as a new species, without regard to the tax- onomic consequences of the application of this policy to sexually differentiated higher animals. If similar results justify the predication of similar causes the 2j6 COOK appearance of similar mutations under diverse conditions may- be accepted as proof that they were induced by the common condition of inbreeding. Otherwise it would be necessary to suppose that different topic factors have produced like results, all of which shows the hopelessness of connecting mutations with environment. Mutations represent abnormally accentuated individual differences, and it seems not unlikely that most of them follow lines of variation already established within the species.1 It has been found in all the species thus far canvassed that a few mutative tendencies are much more frequently shown than the others. Nevertheless, it is not safe to assume that the same mutation reappears even twice in identical forms. Whenever two similar mutations of coffee, cotton, or Capsicum have been brought together and compared they have always been found to be very distinctly different, even more so than the unmutated individuals of the uniform type from which they have arisen. 3. EVOLUTION, SPECIATION AND ADAPTATION. One of the most frequent causes of confusion and error in evolutionary thought is the failure to distinguish clearly between evolution, speciation and adaptation; to distinguish, in other words, between the process of evolution itself and two of the relatively incidental results of environmental interference. As long as a group of organisms remains united so that all its members interbreed freely with each other, evolution remains a unit in the sense that the whole group, though it may be chang- ing any or all of its characters, still keeps together and retains its specific coherence. But if such a group be split into two or more parts which do not interbreed, evolution has as many separate courses, and the isolated parts attain differential char- acters, or, to use the words of former days, new species origi- nate. It is obvious, however, that the differentiation of the new groups, while accomplished by evolution, is occasioned by isola- tion.2 The multiplication of groups, which as a process may be 'The oranges, lemons and pomelos afford, according to Mr. W. T. Swingle, many excellent examples of this parallelism of mutative variation. 2 Confusion often creeps in at this point from the field of geology, for the paleontological species is usually a random sample or section of the network of ASPECTS OF KINETIC EVOLUTION 277 called speciation, is brought about by isolation, and is not a necessary cause nor a necessary result of evolution. In a similar way another group of evolutionary writers have confused evolution with adaptation. Evolution results, not un- commonly, in the production of characters which give a species a specialized fitness for some particular environment. From such facts it was argued that the increase of fitness or " survival of the fittest" represented the method of evolution, or in other words, that evolution is merely a process of adaptation actuated by the selective power of the environment. The facts of nature show, however, that evolutionary motion is not at all restricted to directions of fitness, and it is also obvious that an evolution so restricted could not produce even the characters of fitness upon which it would depend for its supposed power to transform species. Fitness must be attained by evolution before the envi- ronment can give the character selective specialization by limit- ing the evolutionary motion and deflecting it into more definitely adaptive directions. Evolution is the process of change by which the members of an organic group become different from their predecessors, or from other groups of common origin. Symbasis is the normal evolutionary condition of free and ex- tended interbreeding among the individual members of natural species. Symbasis implies adequate diversity of descent ; it is to be distinguished on the one side from the narrow inbreeding which induces abnormal mutations, and on the other from the wide cross-breeding which produces abnormal hybrids. The continual interweaving of the lines of descent from diverse and unrelated ancestors appears to be necessary to sustain the vitality and evolutionary progress of the higher plants and ani- mals. The constructive evolution of new organic types does not take place on simple or narrow lines of descent, but requires descent. When considered with reference to each other, the contemporaneous species of a horizon have the same significance as species of the present day, but species of different horizons may have a relation which two simultaneous species would never have, that is, one may be the true ancestor of the other. The same word species is used for several categories of organic groups. See, Four Cate- gories of Species, American Naturalist, April, 1899. 278 COOK that large numbers of organisms advance in company, as in specific groups A species is an organization of diverse, inter- breeding individuals, dependent for its continued existence upon its ability to maintain a broad and intricately interwoven net- work of descent. Speciation is the attainment of differential characters by seg- regated groups of organisms, that is, by subdivisions of older species. Isolation of an organic group implies such a separation that interbreeding with members of other groups is excluded. Isolation is of primary importance in speciation, since isolated groups of organisms always become different, but there is no indication that isolation is an evolutionary factor in the sense of causing or contributing to organic development. Its influence is negative rather then positive, for small groups of individuals advance less rapidly then large, and often deteriorate through inbreeding and inadequate diversity of descent. The multiplying of species is a process distinct from develop- mental progress, and constitutes a distinct scientific problem. Evolution might be explained without explaining speciation, and speciation without explaining evolution. Recognition of the diversity of the problems enables the factors to be separated ; evolution depends upon symbasis, speciation upon isolation. The segregation of a new group, whether by geographic barriers or by selective discrimination, merely affords opportu- nity for a new evolution to go forward. The means by which the progress is accomplished are to be sought inside the group, and not in the mere fact of isolation or selection. The multiplica- tion of the number of evolving groups is a phenomenon distinct from that of the evolution itself. The evolutionary question is not how the species become isolated, but how they become dif- ferent after they have been isolated. Adaptation is the attainment of characters which place the species in a more advantageous relation with its environment. Selection is a form of isolation which eliminates from the spe- cies individuals lacking in the expression of certain characters. Under unconscious or natural selection only the most deficient in these characters are rejected ; under conscious or artificial ASPECTS OF KINETIC EVOLUTION 279 selection by man only the most proficient are saved. Selection, by deflecting and confining the evolutionary motion of the species to particular channels, conduces to the adaptive speciali- zation of characters, but it is not an actuating cause of their development. Symbasis is a primary factor in evolution, an obstacle or neg- ative factor in speciation. Selection often accounts for the accentuation of differences between related species, but is not on this account to be reckoned as an actuating cause or principle of evolution. It may explain the direction which evolution has taken with reference to a particular character, but does not show how the evolution has been accomplished. Adaptation represents the bionomic aspect of evolution, specia- tion the taxonomic. Selection strengthens adaptations ; isola- tion multiplies species; symbasis conducts evolution. Adapta- tion and speciation have appeared to many writers as causes of evolution, but in the kinetic or physiological interpretation they appear only as results, quite incidental to the true evolutionary process of progressive change in species. RELATION BETWEEN HETERISM AND SPECIATION. Recognition of the phenomena of heterism, the normal diver- sity of the interbreeding members of specific groups, is neces- sary, perhaps, to a full appreciation of the preceding distinctions between evolutionary change or vital motion and the subdivi- sion or multiplication of species. Although commonly treated together, or even indiscriminately confused, these two processes are quite distinct. They may even run counter to each other, for evolutionary progress is not assisted by the subdivision of a subdivision of a species, but more likely to be hindered. The larger the number of interbreeding individuals the larger are the possibilities that desirable variations will appear, and the wider are the opportunities of a progressive utilization of a new feature. The group, as a whole, will advance more rapidly than if the range of transmission be narrowed by subdivision. Segregation permits the subordinate groups to become dif- ferentiated, but it does not conduce to the advance of the whole series. The newly segregated groups become capable of tax- Proc. Wash. Acad. Sci., January, 1907. 280 COOK onomic recognition as species, but this is a mere incident of evolution, not an actuating cause nor a necessary effect. The recognition of heterism or diverse, alternative descent, and the frequent development of sexual and other specializations of heterism inside specific lines, shows that the subdivision of species is to a very small extent, if any, the direct result of evo- lutionary advance. Not only can diverse characteristics exist inside specific lines, but it is an advantage to maintain just such heterogeneity. The only condition in which heterism would directly conduce to the formation of a new species would be that of alternative characters which hindered interbreeding. It is conceivable, for example, that a species might contain at the same time variations both toward earlier and later flowering, and that, instead of counteracting each other, both tendencies might become gradually more accentuated. The incidental result would be that interbreeding would cease and two separate groups would become established.1 In such a case it might well be claimed that evolution had directly resulted in the multi- plication of species, but it would still be true that it had done so only by means of segregation, and would show only that evolution might result in segregation, not that segregation is a factor in evolution, as often supposed. Isolation is an important consideration in phylogeny or historical biology, which under- takes to tell why the species are in the places we find them. But isolation and species-subdivision have only a remote aud incidental connection with evolution ; they do not cause the pro- gressive change. The confusion of evolution with speciation has greatly impeded the progress of evolutionary science by withdrawing attention from the real issues to relatively unimportant considerations. It has misled many students of evolution into the belief that isolation or segregation is an important factor of evolutionary progress, whereas its influence is negative rather than positive. The selection doctrine of Darwin and the mutation doctrine of De Vries are both theories of speciation rather than of evolution. ^he hickory-borer {Clytus f ictus) and the locust-borer {Clytus robinice) are very similar species, and the females are quite indistinguishable. The perfect insects of the former emerge however, in June, those of the latter in September. See Packard, A. S., 1880, Guide to the Study of Insects, p. 497. ASPECTS OF KINETIC EVOLUTION 28 1 They hold that new groups have to be isolated, that new species have to be made, in order to originate and preserve new char- acters. " Each new variety or species, when formed, will generally take the place of, and thus exterminate its less well-fitted parent. This, I believe to be the origin of the classification and affinities of organic beings at all times ; for organic beings always seem to branch and sub-branch like the limbs of a tree from a common trunk, the flourishing and diverging twigs destroying the less vigorous, the dead and lost branches rudely representing extinct genera and families." Evolution, on this basis, would not be a process of transfor- mation so much as of elimination and substitution. The parental type remains relatively stationary and unmodified until the new form can expand and replace it. The same is true of the mutation theory of De Vries, except that the new variations are supposed to be larger. The new character can persist only as it is able to crowd out its parent or neighbor and to conquer for itself a place in nature. Every new character which has been preserved, must, under these theories, be environmentally useful, which a very large proportion of the characters and differences of plants and animals are not, as even the most pronounced Darwinians like Professor Lankester now admit. The kinetic theory does not encounter these difficulties and im- probabilities. It recognizes speciation and evolution as entirely distinct problems, and does not require that a new species be made in order to preserve a new character, or even that char- acters must be useful. Characters may be preserved even when they are harmful, and may contribute to the extinction of the species. Evolution, in the kinetic theory, is definitely a proc- ess of transformation by the adoption and propagation of new variations in existing species. New variations are not segre- gated from the parental type, but interbreed freely with it, and thus bring about its evolutionary progress. SELECTION EXPLAINED BY EVOLUTION. As so often happens, the philosophical abstractions of logic have yielded very little assistance in the comprehension and 282 COOK description of the facts of evolution. Numerous attempts have been made to define the relations of selection and evolution by means of Aristotle's categories of causation. Perhaps the best example of this is by Professor Cattell : " In discussions on the theory of evolution we find Neo-Dar- winians saying that ' natural selection ' is the cause of the origin of species, and Neo-Lamarckians saying that the environment and the movements of the animal are the causes of adaptations. Now in these cases the word ' cause ' is used ambiguously, igno- rance of the facts of evolution being concealed by the exhibition of ignorance of logic. " I wonder how many men of science have read Aristotle, or understand his distinctions between material, efficient, formal and final causes. We are not here concerned with a formal cause, the idea or plan of a thing, nor with a final cause, the end for which it is made ; but no student of organic evolution can afford to ignore the distinction between material and efficient causes, or between the occasion and the efficient cause of an event. The material cause is that of which a thing is made, one of the occasions or necessary conditions of its existence ; the efficient cause is that which produces a thing and makes it what it is. When no qualification is used cause should mean efficient cause or vera causa. " ' Natural selection ' is no cause of the origin of species, but may be the cause of the annihilation of unfit species. Whether or not the environment, or consciousness, or the movements of animals are causes of hereditary modifications are open ques- tions. What is called the cause of an adaptation is, however, usually only its occasion."1 Selection is neither a formal, a final, a material nor an effi- cient cause of evolution. Evolution goes on without selection. This shows how poorly adapted the Aristotelian categories are for the expression of relations so complex as those of evolution. Those who depend upon systems of abstract formulation for the comprehension of biology can fit selection and evolution into these categories only by saying that evolution is the cause of 'Cattell, J. McKeen, 1S96. The Material and Efficient Causes of Evolution. Science, N. S., 3 : 66S. ASPECTS OF KINETIC EVOLUTION 283 selection. This, at least, would not wholly misrepresent the facts of nature, for evolution accomplishes the results which it has been customary to ascribe to selection. Unless evolution were going on the selective effects would not appear. The older writers commonly made the confusion even worse by assuming that adaptation and evolution are the same. Adaptation is not evolution, but only a special kind or result of evolution. Selection aids evolution to produce adaptation. Translating again into scholastic language, evolution is the efficient cause of adaptations, while selection is the occasional cause or condition which conduces to adaptations. Adaptive characters are brought into existence in the same way as other characters, by the evolutionary motion of species. Adaptation can be said to be caused by selection only as a pure abstraction, when it refers merely to the deflection which environmental obstacles have induced in the normal motion of the species. The confusion of ideas has not been limited to advocates of natural selection, but is shared even by its most active opponents. Thus Mivart, in a book written to show the inadequacy of the selective theory of evolution, admits for selection a power which it does not have : " ' Natural Selection,' simply and by itself, is potent to explain the maintenance or the further extension and development of favorable variations, which are at once sufficiently considerable to be useful from the first to the individual possessing them. But Natural Selection utterly fails to account for the conserva- tion and development of the minute and rudimentary beginnings, the slight and infinitesimal commencements of structures, how- ever useful those structures may afterward become."1 As long as we fail to perceive that selection is not a cause of evolution the issue remains uncertain. If selection is able to cause even a little evolution it might, with time, cause much. The " slight individual differences" may suffice for the work, as Darwin claimed, and the practicability of a selective evolu- tion appears to turn on such arguments as the amount of time estimated by geologists and physicists from considerations even more obscure than those of biology itself. Selection is not 1 Mivart, St. George, 1871. On the Genesis of Species, New York ed., p. 35. 284 COOK merely inadequate as a cause of evolution ; it is not an evolu- tionary cause at all, but only a test and an evidence of the effi- ciency of other causes which reside in the species and enable it to go forward with persistence, even when obliged to follow a narrow path between environmental obstacles. Selection is potent to explain the further extension and devel- opment of favorable variations only by its ability to influence an evolution which is already in progress, and not in any sense which renders it a cause of evolution. The selective potency of the environment consists only in its ability to restrict evolu- tion, not in any power to actuate or to carry forward the process of development. Selection may still be enumerated as an evo- lutionary factor, but it is wholly a negative factor, restrictive and not constructive. DARWINIAN FORMULAE OF EVOLUTION. Evolution is a name for the process of gradual change by which the diversity of organic nature has come about. Darwin's theory of natural selection was based on the indication that some of the characters of plants and animals have been attained because individuals possessing these characters had an advan- tage in the struggle for existence. Many Darwinians " more Darwinian than Darwin " have made this proposition universal and say in effect that all characters of plants and animals have arisen because they give or have given their possessors advan- tages in the struggle for existence. Darwin's original proposition points in the direction of an im- portant truth, that plants and animals are specially adapted to their various environments. Great emphasis came to be placed on this point because the adjustment of species to their respec- tive places in nature had been taken to prove the special crea- tion of species, so that a theory of gradual development had to supply a solution for the problem of adaptation before it could expect to receive general credence or even the serious con- sideration of the scientific public. In the course of the discussion which raged in the decades after the publication of the Origin of Species attention was prin- cipally directed to the phenomena of adaptation and speciation, ASPECTS OF KINETIC EVOLUTION 285 and the Darwinian doctrines were crystallized into formulae which were believed to demonstrate evolution from the facts of the struggle for existence and the survival of the fittest. PROVED FACTS. NECESSARY CONSEQUENCES. Rapid Increase of Organisms. "1 _ . . _ . m itvt ^ i-r j- -j i ox »• ^Struggle for Existence. 1 otal Number of Individuals stationary. J Struggle for Existence. "i _ . , . . „. , TT b° . , TT . . ^Survival of the Fittest. Heredity with Variation. J Survival of the Fittest. \ Changes of Organic Change of External Conditions. J Form. The earlier Darwinists were practical men and made the best use of the facts as they knew them. Whether the facts they regarded as proved would really be able to bring about evolution in normally stationary species is a question which might still be debated on philosophical grounds, like the fourth dimension of space and other hypothetical problems. But for practical pur- poses there is no need to reopen the discussion, since it is now apparent that formulae like those quoted above leave out of account a very important part of the facts of nature, the very facts, as it happens, which are most potent in the development of organic types. The evolution, if any, which the formula would provide would certainly not be that found in nature. Scientific progress, at least in biology, does not follow the lines of formal mathematics or logic, but depends on history and human nature, like political and economic movements. It could not be expected that the evidences of evolutionary processes would be carefully weighed and correctly appreciated at a time when the very idea of evolution was being assaulted as an im- moral perversion of intellect. The best that could be done at the time was to drive the piles of accepted inferences into the mud of ignorance. The struc- ture reared on such a foundation could not be a permanent one, but it has served to shelter a generation of students of nature, and enabled them to prepare the foundations of a more secure edifice of evolutionary doctrine based directly on ascertained facts. 286 COOK In popular discussions it often happens that the best and most important data are left in the background because the public is not ready to appreciate them. Thus Huxley, who rendered the most valiant service in the defense of Darwinism as a theory of environmentally caused evolution, also wrote this discriminating statement : " It is in the recognition of a tendency to variation apart from the variation of what are ordinarily understood as external con- ditions that Darwin's view is such an advance on Lamarck." To have secured popular appreciation for these nonenviron- mental variations at that time was manifestly impracticable. Even after fifty years their existence is still generally unrecognized. The credit of turning the scientific world to the study of evo- lution will always belong to Darwin and Huxley, but the fifty- years canvass which has now been given to the Darwinian theory of environmental action upon normally stable species has yielded nothing of moment. Huxley's appreciation of the advance of Darwin beyond Lamarck has not been shared by the evolutionary public, and the result has been a general reaction toward pre-Darwinian conceptions, and even to some which Darwin himself considered and dismissed.1 Perhaps the time has come to renew the consideration of the problem from the kinetic standpoint and to take into account again the normal diversity of descent and the normal inter- breeding of the members of species. These facts have re- mained veritable stones of offense for the builders of static theories of environmental causation, but they can now be util- ized as foundations of a new and more commodious structure of evolutionary thought. 4. MODES OF EVOLUTIONARY MOTION. The law of evolution which declares that organic nature has come into existence through a connected and gradual process, and not through millions of separate creations of species, now commands the practically universal adherence of biologists, and 1 " And again, after mentioning the frequent, sudden appearances of domestic varieties he speaks of ' the false belief as to the similarity of natural species in this respect.'" See Mivart, 1S71. Genesis of Species, 36. ASPECTS OF KINETIC EVOLUTION 287 has also been applied as a philosophical principle in the elucida- tion of many facts and problems outside the organic series. After being once adequately presented such an integration of knowledge could scarcely have failed to command respectful consideration, and its general acceptance has already become so much a matter of course that the word evolution is not uncom- monly used in a much narrower sense and identified with one or the other of the theories which have been invented to explain the methods and immediate causes of the process of organic change, a subject upon which there is still no lack of differing opinions. Although the doctrine of the independent creation of species has been set aside, it has proved much more difficult to elimi- nate, even from the minds of the biologists themselves, what may be called the static view of nature. It is not strange that the stability of species should have first impressed the scientific mind. When closely similar plants and animals, not distin- guished by the popular intelligence, were found to differ in minute particulars which were, nevertheless, invariably trans- mitted to their offspring, a creative pre-arrangement seemed to be the only explanation, and the apparently gratuitous variety of organic forms was very naturally ascribed to causes outside the reach of human comprehension. Later, when it was realized that in spite of the wonderful sta- bility of species the component individuals are never identical in all particulars, but differ endlessly among themselves, and that even these minor differences tend to reproduce themselves, the theory of the gradual transformation and subdivision of spe- cies became a logical possibility, and the search at once began for a method by which variations of a certain kind could be accumulated instead of cancelling each other and disappearing in a stationary average. The explanation of evolution is the biological task now re- ceiving the widest and most earnest attention, and is the subject, directly or indirectly, of a literature so vast that even a casual reading of all the books and papers as they come from the press would be a formidable undertaking. Such multiplicity of pub- lications betokens, of course, a corresponding diversity of opin- 288 COOK ions. Not only is there no common point of view from which evolutionary problems are studied ; there is no agreement re- garding the nature of the problem or the methods by which a solution is to be expected, nor even a general evolutionary language in which discussion may be made intelligible. Explanations of such a process as evolution are of many dif- ferent grades or categories. Literary demands were satisfied by a name and a definition ; theologically it was sufficient to substitute the idea of a continuous for an intermittent creation. Philosophy was content with the predication of gradual trans- formations due to natural causes. Even among biologists there are those who appear to have rested content with similar gen- eralities, though some have not failed to appreciate that when Darwin established the probability of biological evolution he opened a multitude of other questions regarding the nature, causes and significance of the process. Realizing at once the importance of his discovery and the difficulty of securing the confidence of either the scientific or the general public, he ex- pended years of labor in the collection of facts and the con- trivance of theories which should increase the plausibility of the main proposition, that plants and animals are variable, both in nature and in domestication, and that the diversity of organic nature was gradually attained through the medium of variations. When the causes of a phenomenon are known the sequence of events can be predicted. Theory may then out-run and assist observation. On the other hand, if the causes are out of reach it is obvious that we can not even theorize to advantage without a correct conception of the externals. We must know what takes place before we are in a position to ask why it takes place. In some lines of thought the simple historical concep- tion of continuous evolutionary change greatly assists in the causal explanation of events, but in biology, the home of the evolutionary conception, the sequence is still in doubt and we are still far from the causal stage of knowledge. It is needless, perhaps, to add that the application of false and fictitious biological analogies vitiates much philosophical and sociolog- ical literature. Gravitation was not explained by Newton, its behavior was ASPECTS OF KINETIC EVOLUTION 289 carefully studied and found to be consistent, and mathematically precise. "Natural laws" are working substitutes for causal explanations. When we understand the ^>/iy, the ' law ' of sequence becomes superfluous. There is a frequent impression that the principal object and result of scientific study is generalization, but as a matter of fact the progress of science leads much more often to particulariza- tion, to the recognition of distinctions between things previously supposed to be alike. The powers, forces and principles which formed the subject of abstract discussions in the earlier history of science are being gradually relegated to the background, as our acquaintance with the facts improves and yields insight into the causal connection of events which formerly appeared mere sequences. Evolution is not merely a law, but a process. In each species an evolution is going on, in a manner quite analogous to the processes of growth, locomotion and reproduction in the indi- vidual. Certain features of similarity there are, no doubt, in all evolutions, as there are in digestion and other general forms of vital activity. These general similarities can be collected, it may be, and formulated as laws if this method of expression be desired, though this would be, after all, only a special method of describing the processes. Laws themselves have to be ex- plained by resolving them into processes. Only hopelessly metaphysical minds are satisfied with abstract statements, or able to imagine that generalizations are explanations. Evolutionists agree that organisms change, but regarding the nature and causes of change great diversity of opinion still exists. The progress thus far is negative. We have learned that evolution is not a merely mechanical process, or due to merely environmental causes, and that it is not a merely cyto- logical process, due to internal mechanisms of descent. It is a superorganic process accomplished through the association of organisms into large specific groups. Evolution is, in short, a process of change in organisms, a kind of motion by which plants and animals have advanced from the simple and undifferentiated protoplasm of the lowest types to the highly specialized and complicated structures of the 29O COOK highest. For half a century this probability that the world of organism has come into existence through long series of changes has been the most prominent idea before the scientific public, but we have not yet accepted fully the simplest purport of the idea of evolution and asked ourselves the direct question : By what mode or manner of motion is evolution accomplished? Some have assumed that the evolutionary causes are resident in the environment, and others that they exist in the organisms themselves. A third alternative is here considered, that evolu- tion arises from the association of organisms into interbreeding groups, or species. Species, in this interpretation, appear to contain the causes of evolution, instead of evolution affording the explanation of species.1 The first result of Darwin's attempt at establishing the general idea of evolution on a basis of relation to concrete facts was a long and bitter controversy with those who clung to the older theory that the species of nature had arisen by separate creative acts. Biological science made good its escape from the house of theological bondage, but its controversial sins have con- demned it to forty years of wandering in the wilderness of species-formation and environmental adjustments, desert regions often very interesting in themselves, but remote enough from the fertile fields of evolution. It may well be doubted whether any student of nature, if asked the direct question, whether species are normally at rest or normally in motion, would definitely and dogmatically hold to the static assumption. This appears to have been made quite unconsciously, in the great majority of cases, or taken entirely for granted. Nevertheless, all the current theories and methods of investigating evolutionary problems are based on this assump- tion of normally stationary species. The influence of the doctrine of special creation was too strong to be overcome at once, even by biologists who were very active in opposing its theological implications. The idea of environmental causation of evolution has com- 1 Cook, O. F., 1904. Evolution not the Origin of Species, Popular Science Monthly, for March. Reprinted with additions in the Smithsonian Report for 1904 under the title, The Evolutionary Significance of Species. ASPECTS OF KINETIC EVOLUTION 20,1 pletely pervaded all our forms of thought and expression ; it has been the general base and background of evolutionary science. The average of biological opinion remains very nearly in the same place as Darwin's original announcement of a theory of environmental causes of evolution. The environment is sup- posed to bring about the variations and to select and preserve those having adaptive value, and thus to cause evolution. Though Darwin himself appreciated in later years the tentative character of this inference and sought in every direction for contributing agencies to strengthen and support it, some of his followers have had no such reluctance in crystallizing the idea of environmental causes into definite formulae which are still the shibboleths of evolutionary orthodoxy. President David Starr Jordan not long ago quoted an interesting paragraph from the evolutionary creed of the late Dr. Eliot Coues : " Every offspring tends to take on precisely the structure or form of its parents, as its natural physical heritage ; and the principle involved, or the law of heredity, would, if nothing interfered, keep the descendants perfectly true to the physical characters of their progenitors ; they would breed true and be exactly alike. But counter influences are incessantly operative, in consequence of constantly varying external conditions of environment ; the plasticity of organization of all creatures ren- dering them more or less susceptible of modification by such means, they become tinlike their ancestors in various ways and to different degrees. On a large scale is thus accomplished, by natural selection and other natural agencies, just what man does in a small way in producing and maintaining different breeds of domestic animals."1 It should be needless to say that this formula, like many statements of similar import which might be collected from biologists of a former generation, and even from those of the present day, involves a complete misrepresentation of the facts. No such species has been found in nature, and no species has been made uniform by an}' refinement of artificial conditions. It is possible through selective inbreeding to eliminate a large part of the normal individual diversity of organisms, but at the 'The Popular Science Monthly, May, 1903. 292 COOK expense of vitality, and at the ultimate cost of extinction, where- ever such experiments are continued for a sufficient period of time. More recently still, a son of Charles Darwin, speaking as President of the British Association for the Advancement of Science, has reflected the conclusion which the scientific world has drawn from his father's doctrine of natural selection, that it is the cause of evolution. " The fundamental idea in the theory of natural selection is the persistence of those types of life which are adapted to their surrounding conditions, and the elimination by extermination of the ill-adapted types. The struggle for life amongst forms possessing various degrees of adaptation to slowly varying con- ditions is held to explain the transmutation of species."1 It may be doubted whether Charles Darwin himself would ever have ventured upon so direct and so generalized a state- ment. He was anxious always that his readers should take a favorable view of the feasibility of evolution through natural selection, but at the same time he could not forget the immense improbability of the claim that all characters are adaptive and useful. This caution was not shared by Wallace, who has never hesitated to proclaim selection as the cause of evolution, alike efficient and sufficient. With Darwin, natural selection remained a theory, and he never ceased to seek additional evi- dence to support or supplement it, but with Wallace and many others it soon became an undoubted fact, or at least an unques- tioned formula. " Suffice it to say here that this theory of natural selection — meaning the elimination of the least fit and therefore the ulti- mate 'survival of the fittest' — has furnished a rational and precise explanation of the means of adaptation of all existing organisms to their conditions, and therefore of their transforma- tion from the series of distinct but allied species which occupied the earth at some preceding epoch. In this sense it has actually demonstrated the ' origin of species,' and, by carrying back this process step by step into earlier and earlier geological times, we 1 Darwin, G. 11., 1905. Address of President of the British Association for the Advancement of Science; Nature, 72 : 370. Science, N. S., 22 : 258. ASPECTS OF KINETIC EVOLUTION 293 are able mentally to follow out the evolution of all forms of life from one or a few primordial forms. Natural selection has thus supplied that motive power of change and adaptation that was wanting in all earlier attempts at explanation, and this has led to its very general acceptance both by naturalists and by the great majority of thinkers and men of science."1 But notwithstanding the categorical certitude of these and many similar statements which might be collected, it is still very doubtful whether any naturalist, that is, any careful and experienced student of plant or animal species in nature, would definitely claim or undertake to prove that isolation or natural selection is, or could be, a true, actuating cause of evolution. Nevertheless, many such students have permitted themselves to use expressions which can be so interpreted, and the philo- sophical, and especially the unbiological part of the scientific community, has not hesitated to repeat and elaborate this idea as though it were an ascertained and undeniable fact. Primitive peoples are ever ready to personify nature and in- animate objects and to ascribe to them the ability to grow and to put forth other spontaneous actions. Modern science has gone to the other extreme. It has denied to the species of plants and animals the powers of development which they really possess, and has sought for the causes of organic evolu- tion among the inanimate objects of the environment. It has done this quite gratuitously and as a matter of course, without taking the trouble to raise the question whether there might be any alternative worthy of consideration. The primitive theory of a flat earth, with its various childish explanations of the sun's whereabouts during the night, endured for thousands of years, but finally gave place to the conception of a spherical earth, about which the luminary revolved contin- uously. Nevertheless, this improved doctrine, while adequate for the explanation of the phenomenon of days and nights, was also erroneous, and had to be replaced by a still broader inter- pretation of astronomical facts. Astronomers of the Ptolemaic school saw no reason to doubt that the earth was stationary, and they were able to predict 'Wallace, Alfred Russell, 1900. The History of the Nineteenth Century. 294 COOK eclipses and planetary movements in spite of this fundamental misconception. Mysteries and discrepancies remained, how- ever, until students of the heavenly bodies were willing to admit that the sun was the center of the system and that the earth revolved like her sister planets. If adaptations were the only evolutionary phenomena in need of explanation, the doctrine of environmental causes might serve scientific purposes for as many centuries as the Ptolemaic astronomy, but it has become very apparent that many organic changes are going on which have no connection with adapta- tion, and which would not be explained by selection, even if everything claimed for it were to be admitted. To think of species as normally in motion will be found very difficult, no doubt, by those who have been so long accustomed to take it for granted that they are normally at rest. The dif- ficulties of readjustment are still further increased by the fact that the available technical language and customary forms of expression have been elaborated for the exposition of the static doctrine of environmental causation, and lend themselves only with difficulty to the presentation of the opposite doctrine, that species are normally in motion.1 Many distinctions formerly considered of value now appear to have little significance. Many things are readily explainable which seemed utterly mysterious before, and many new problems can be approached which have hitherto appeared quite inaccessible. Since the time of Darwin a long and varied series of amend- ments and supplements have been proposed for the doctrine of natural selection, and no end of diversity of individual opinion has existed among biologists regarding the adequacy and relative significance of the various factors and forms of selection. The kinetic theory enables us to look beyond all this cloud of discussion and to perceive that selection is not merely inadequate as the cause of evolution ; it is not an evo- lutionary cause at all, in the concrete physiological sense ; it does not set evolution in'motion, nor keep it going. 1 Three classes of difficulties attend the progress of science, the concrete diffi- culties of ascertaining facts, the conceptual difficulties of interpreting them, and the philological difficulties of describing the new facts and the concepts in terms of general intelligibility. The problems of expression are often quite as serious as the others, and quite as worthy of scientific study. ASPECTS OF KINETIC EVOLUTION 295 The difficulties which attend the presentation of the kinetic theory arise, no doubt, largely from this fact, that it breaks with the Darwinian traditions and recants the whole doctrine of selection as the actuating cause or principle of evolution. It seeks for the laws and causes of evolution, not in the environ- ment, nor in a "hereditary mechanism" of the organisms themselves, but in the association of organisms into specific groups of interbreeding individuals, which are the units of evolutionary motion. The reader is therefore duly warned that, unlike most of the suggestions made since the time of Darwin, kinetic evolution does not come as an amendment to natural selection. Those who may wish to experiment with the new method of biological locomotion had best unload beforehand all their pre- possessions regarding natural selection as an evolutionary cause. This does not mean that selection is to be permanently aban- doned, but it can be taken up later, and put to a much more useful purpose than before. Indeed, the material analogy may be carried a step further by saying that the supposed evolu- tionary properties of selection have been due to an unsuspected admixture of kinetic implications, the selection idea in itself being quite inert, and incapable of actuating even a logical conception of evolutionary motion. Theories which located the causes of evolution in natural selection or other forms of environmental reactions have con- sidered the species normally stationary until acted upon by the external forces. Theories which located the causes inside the organisms have thought of evolutionary motion as proceeding in definite directions without regard to environmental influences, except as they might work the extermination of types poorly fitted to the conditions they happened to encounter. The kinetic theory, in appreciating the fact that the evolutionary change goes forward in a network of descent woven by the free inter- breeding of the individual members of the specific group, reaches the conception of a highly composite, indeterminate motion carried along without any environmental causation, but at the same time capable of being deflected through selective influence into channels of adaptation. Proc. Wash. Acad. Sci., January, 1907. 296 COOK The most feasible way of presenting the kinetic interpretation and of comparing it with other alternative views has seemed to be that of canvassing further this question of the nature of the motion by which evolution is supposed to be accomplished in accord with the different doctrines. It may be that by so doing the issue can be made more direct and that there will be less risk of wandering into the unprofitable side-paths of aimless discussion. The fact already referred to, that the vocabulary of evolution has been constructed so largely for the explanation of static doctrines, makes it necessary to review briefly some of the primary terms and distinctions. . PHILOSOPHICAL USES OF EVOLUTIONARY MATERIALS. Circles can be described through any three points, and new systems of philosophy can be elaborated out of a few primary distinctions. As geometry and other speculative sciences of number and space relations have been called upon to assist in the measuring of land, the building of machines, the naviga- tion of the sea, and the exploration of the heavenly bodies, so have the methods of philosophy been applied to evolution. This is not only because philosophers have become interested in evo- lution, but because philosophical systems are the most available form of mental machinery for dealing with complex miscel- laneous, hypermathematical problems, like evolution. It has been the ambition of philosophers to frame general descriptions of the universe of thought in terms of logical con- sistency. Indeed, the tendency in philosophy has been to place by far the greater emphasis upon the logical consistency, each philosopher assuming the right to choose his own particular universe for descriptive purposes. Unfortunately for evolu- tionary philosophers, their systems are confronted, sooner or later, with the concrete facts of plant and animal life, and then no amount of logical consistency can atone for a biological over- sight. Theories may be perfectly logical and yet be utterly inadequate. But even though not correct or final, philosophical theories of biology may still amply justify themselves by aiding in the discovery of relations which might have remained unsus- pected and hence uninvestigated. The ungrateful facts may ASPECTS OF KINETIC EVOLUTION 297 refuse to support the theory which has led to their discovery, but this does not render the facts of less value for practical pur- poses, nor even for use in other and better theories. It is as idle to condemn theories as to worship them ; it is the old counsel of using and not abusing. Theories of evolution have been made thus far from the facts of variation, the differences which exist among the members of the same species. In each of the different systems it has been assumed that a certain kind or group of variations represented steps in the evolutionary journey. The philosophical circles of doctrine have been described in different planes in accordance with the selection of particular lines of samples from the multi- tudinous facts of variation. The theory of natural selection is supported by the facts of adaptation and geographical distribution. The theory of direct adaptation was based on variations of accommodation, on the fact that organisms are often able to adjust themselves to a con- siderable range of environmental conditions. Nageli's deter- minant theory was based on the fact that the plants most care- fully studied by him showed tendencies of variation in definite directions. The theory of mutation rests on facts of abrupt modifications in the form and structure. The kinetic interpretation claims the consideration of believers in the other doctrines because it affords a larger outlook upon the facts of nature. Adaptation and mutation no longer appear as unconnected or contradictory phenomena, but are completely reconciled under one simple inference. The kinetic theory differs from its predecessors not merely nor principally in dependence upon a different series of facts of variation, but also in the method of combining them. It is not merely a circle cut in one plane or described on one cross- section of data, but considers all three dimensions of space. It permits us to understand that variations are not all of the same character or of the same evolutionary significance. It also recognizes that as species are networks of descent and not mere aggregates of similar organisms, so evolution is not merely a summary or integration of variations, but is accomplished only through the normal extension of the specific reticulum. 298 COOK In pre-evolutionary days there was no need to make special studies of variation, since it was freely admitted by the scientific public that the differences of varieties and even of species arose from environmental influences upon normally stationary types. The supposition was that genera had been created, rather than species, though Linnaeus interfered with this view by combining many of the groups recognized by his predecessors as genera and by holding then that species also were specially created. The significance of this history is that the two ideas, first, that of normally uniform and stationary species, and second, that of the environmental causation of variations, were inherited from the pre-evolutionary period and have continued to be used with- out scientifically critical warrant. Moreover, the first quest for evolutionary causes was not made in the direction of more thorough study of the constitution of species, but was concerned rather with the exploration of the boundaries and the gaps between species. The issue raised by Darwin, and more especially by Huxley and other controversial biologists, was that of proving to the theological public that new species could be produced by evolution, instead of definitely investigating the means by which the evolutionary progress of species is accomplished. The chief interest was directed, not to evolution itself, but to the two results of evolution, speciation and adaptation, the generally admitted pre-Darwinian doctrine of environmental causation of variations serving all the imme- diate needs of the discussion. TYPES OF EVOLUTIONARY THEORIES. Static Theories. — According to the theory to which the name Darwinism is generally, though unjustly, limited, evolu- tion is brought about by the influence of environment, which causes organisms to vary, preserves advantageous modifications, diminishes or eliminates the relatively unfit, and thus transforms or subdivides species.1 Such theories may be called static be- cause they assume that species are normally in a state of rest or 1 "Darwin has left the causes of variation and the question whether it is lim- ited or directed by external conditions perfectly open." Huxley, Life and Letters, 2 : 205, 1901. ASPECTS OF KINETIC EVOLUTION 299 stable equilibrium, so that evolutionary motion appears as the result of forces external to the organism. Differences among the individuals of a species are ascribed to environmental causes ; without such disturbing influences the species is thought to remain stationary and uniform. Darwin and many others have believed in spontaneous variations, but it has been argued that such must be ' swamped ' in the general average by intercrossing, so that without the external influence of selection there could be no progressive change. Darwin himself admitted that in the domestic animals ' man does not cause variability and cannot even prevent it,' but on the same page he made the contradictory statement that * the initial variation is caused by slight changes in the conditions of life,' and this has served as the cardinal principle of those who have claimed to be Darwinists, while rejecting the wider per- ception cited above. Again in the same work (p. 79) Darwin is ready to admit that ' a somewhat complex, though apparently useless, structure may be suddenly developed without the result of selection.'1 Saltatory Theories. — That variations can be preserved by selection, and are frequently so preserved among domesticated animals and plants, cannot, of course, be doubted, but the diffi- culty of believing that natural conditions would provide the necessary selection or segregation at the right junctures has led many biologists to look with favor upon the idea that new species have not arisen by imperceptibly gradual changes, as Darwin supposed, but by a succession of leaps, as it were. This view is defended by reference to the so-called ' sports' or very pronounced variations occurring among domestic plants and animals. Mr. Francis Galton has compared the organism to a polygo- nal body which comes to rest at a point considerably in advance of its former position when its equilibrium has been sufficiently disturbed. Professor De Vries has adopted the saltatory view, as a result of his studies of what he calls mutations, or pro- nounced and readily transmissible variations of domestic plants. 1 The Variation of Animals and Plants under Domestication, p. 3, New York, 1897. 300 COOK Instead of slow or gradual changes of the characters of species there are supposed to occur at remote intervals in the life of a species relatively brief periods of mutation in which violently abrupt variations are given off in an explosive manner. Each of these discontinuous variations is considered as representing the production of a new species, there being no gradations be- tween it and the parental type. Unfortunately, the wide appli- cation of this analogy is prevented by the fact that in many natural groups descent from a single individual is impossible. Moreover, the new types or sports studied by Professor De Vries are, like other closely inbred plants and animals, much less fertile than their wild progenitors, thus increasing the probability that the inbreeding or segregation necessary to secure and preserve these abnormalities would give them a fatal handicap in the struggle for existence. Finally, the wide distribution, among both plants and animals, of sexual differen- tiation and other expedients for securing cross-fertilization, seems a sufficient warrant for distrusting any theory which disregards this important group of evolutionary phenomena. Determinant Theories. — The noninheritance of acquired characters led Nageli and Weismann to formulate what maybe termed determinant theories, under which the motion of species is not thought of as caused or directly influenced by the environ- ment, but as the function of internal " mechanisms of descent." Nageli believed that species did not vary in all directions indis- criminately, as Darwin had held, but that they kept, without selective influences, a definite direction. He therefore con- cluded that the organization of living matter contained what he called a " Vervollkommungsfirinzifi" or principle of perfection, which carried them ever upward along the road from simplicity to complexity. Weismann sought in his doctrine of determinants to render this conception more concrete regarding the nature of the in- ternal mechanism, and to provide a means of selective influence. Determinants may be described as biological atoms, resident in reproductive cells and able to determine in advance the charac- ter of the new organism, independent of its environmental rela- tions. The environment also has no effect on the next genera- ASPECTS OF KINETIC EVOLUTION 3OI tion, selection pertaining not to the characters themselves, but to the determinants which might repeat the characters in the next generation. Further elaboration of the doctrine of deter- minants has been made in the belief that the external conditions, while unable to act through the body of the organisms, might act directly upon the reproductive cells. Others assume con- flicts or struggles between determinants (germinal selection) as possible factors in evolutionary motion. As a suggestion that evolution might be the result of external influences, and as a means whereby characters imposed by the environment could be transmitted, Darwin invented the theory of pangenesis, to the effect that the germinal material carrying reproductive influences was assembled from all parts of the body of the parent organism. Direct evidence for this supposition has never been found ; indeed, the contrary proposition, that acquired characters are not and cannot be inherited, has com- manded the belief of Professor Weismann and his numerous followers. Having cut loose, as it were, from environment, which had been the chief resource of static theories, they have sought the explanation of the evolutionary problem in a so-called " hereditary mechanism," by which the characters of successive generations are held to be predetermined in the reproductive cells. The structure of the living cell has accordingly received the attention of many earnest investigators and a new science of cytology has been rapidly built up. But, as in the pursuit of her somewhat older sister, embryology, no general uniformity of structure or processes has been discovered. Biology has been enriched by the addition of a vast number of interesting facts, but the minute structure and internal organs of plants and animals, including the structure and organs of the component cells themselves, have been found to share the general diversity of nature, and to be as much in need of evolutionary explana- tion as the external characteristics of the various natural groups. With an infinity of biological facts to draw upon, no theory need remain without support, real or apparent. An evolu- tionary inference warranted in one group may be quite false as a general law, and in this sense an inadequate theory may be more misleading than one which is actually erroneous. Thus 302 COOK each of these types of evolutionary theories may be said to rest upon certain groups of evolutionary facts which are more or less completely ignored by the others. The niceties of many adapta- tions to environment have led Darwin and his followers to almost exclusive reliance upon that factor. Saltatory theories provide larger variations, but require even more effective isola- tion. Determinant theories deny the influence of environment and must ascribe adaptations to accident or to pre-established harmony. All three theories antagonize the obvious fact that a very general tendency of organic development has been toward the increase of facilities for cross-fertilization. These have been interpreted as inimical to evolution because they interfere with the preservation of the abnormally close-bred variations which have been mistaken for true steps in the progress of organic series. KINETIC OR SYMBASIC EVOLUTION. Somewhat between the doctrines of selection and of deter- mination, but distinct from both, is another conception of evolu- tionary motion, that it is caused neither by external environments nor by internal mechanisms, but goes forward as a necessary result of the normal specific constitution of living matter. It is observed that organisms normally exist and make evolutionary progress only in large groups of interbreeding individuals. Evolution is, in a word, symbasic ; that is, organisms must travel together along the evolutionary pathway, and must be connected with each other by an intricate network of descent in the weaving of which the diversities of the members of a species have a definite physiological value. Without diversity of descent the cellular organization deteriorates. This being the case, it is easy to understand that new variations are pre- potent, and that species make more rapid evolutionary progress in proportion to their numerical size. The larger and more widely distributed the species, the greater the opportunities of variation and of evolutionary progress. Kinetic evolution is thus the reverse of many current theories, in that it recognizes a normal and necessary movement of change not caused by environment. It is the reverse of the selective ASPECTS OF KINETIC EVOLUTION 303 theory of Darwin in holding evolution to be independent of natural selection. It reverses the panmixia doctrine of Pro- fessor Weismann, in that it treats the interbreeding of the numerous and diverse individuals of species as conducive of biological motion, instead of as hindering it. It is the reverse of the mutation theory of Professor De Vries, in that evolu- tion is held to go forward normally in entire species, and not merely in individuals or in narrow lines of descent. One of the chief weaknesses of all the static doctrines, both saltatory and selective, lay in the apparent necessity that new variations be isolated from their relatives in order to preserve their new characters and make evolutionary advance possible, for the fundamental concepts of the static doctrine are the normally stationary average and the swamping effects of inter- crossing. The kinetic theory differs fundamentally from all its prede- cessors in recognizing the fact that evolution is not a process of segregation, but of synthesis and integration. The transforma- tion of species in nature is brought about by the sharing of in- dividual variations through interbreeding. Conjugation and cross-fertilization do not hinder evolution, but are essential to the gradual building up of the intricate coordinations of char- acters through which adaptations and other desirable changes go forward. Selection, inbreeding, isolation and other forms of segregation, reduce the number of accessible variations, narrow the basis of the vital structure, and result in organic weakness, sterility and extinction. Selective isolation accentuates par- ticular variations and has been utilized in the diversification of domestic varieties of plants and animals useful to man, but abnormal and weak from the evolutionary standpoint, and affording no complete analogy with the natural development of organic types. The sterility of many hybrids and the tendency of inbred varieties to produce relatively infertile sports may prove to be explainable by the same fact of inadequate fertili- zation. For want of better words it may be said that the vital tension of inbreeding is too little, while that of hybridity is too great; the normal course of biological evolution lies, obviously, between the two extremes. Evolution, or biological motion, 304 cook appears to be necessary as well as universal. Free interbreed- ing between the members of large organic groups, or species, is the condition under which biological evolution is going forward in nature, and we have no reason to seek its cause in any aber- ration or specialization of structure or function. The fundamental and truly dynamic causes of evolution still lie hidden in the equally unknown causes of genetic variation, but the evolutionary history of a group of organisms is a proc- ess which a kinetic theory adequately explains by supplying physiological reasons and methods. The ultimate theory or stage of evolutionary explanation must await far more complete knowledge of the nature of the phenom- ena to which we commonly refer under such abstract terms as matter and force, expressions which we can neither describe nor define, except in a purely formal manner. Much is gained, however, by the recognition of the fact of normal evolutionary motion, by perceiving that organic development is a kinetic phenomenon, for the species no less than for the individual. Individuals and species are conditioned, but not caused, by their environments ; they descend from other species and from other individuals in continuous series of ever-changing forms. There is an inside as well as an outside physiology of evolution, and it is idle to ignore either the one or the other. To advance from the static to the kinetic point of view gives us ready and practical solutions for many problems which on the static basis bid fair to have required long periods of time and large expenditure of money. It brings also, as does every advance of science, a host of new questions which the static evolutionist could never have asked, such as the rapidity of evolutionary motion and the means of accelerating, retarding or deflecting it. A kinetic theory of evolution does not need to explain varia- tion any more than it needs to explain symbasis and environ- ment ; it accepts these three groups of biological facts, and correlates them as evolutionary factors. Conversely, a theory of variation is not necessarily a theory of evolution ; the two questions may be viewed as quite distinct. The recognition of evolution as a kinetic process does not conflict with a dynamic ASPECTS OF KINETIC EVOLUTION 305 explanation of variation, but contributes to such an achievement by rendering the problem more definite. It affords another conception of how evolution may be accomplished, but a con- ception more comprehensive than those which have gone before ; one which does not depend upon any theoretical or doubtful relation, but upon the well ascertained and universal fact that organisms exist everywhere in species — groups of diverse indi- viduals freely interbreeding to form a complex network or fabric of descent. To some there may appear to be no practical distinction between the static and the kinetic views. Not a few naturalists have entertained truly kinetic conceptions of the facts of organic nature, even while continuing to misrepresent them by the use of the static terminology. For descriptive purposes, such as the tracing of phylogenies, the differences are less important, but fundamental divergence is obvious in approaching the physio- logical questions of methods and causes. The probable truth of a theory does not depend merely upon the number of facts which can be assembled under it, but also upon the coherence and practical consistency of the relations alleged. Of two theories otherwise equal the more simple and direct should receive the greater confidence. The kinetic theory is not compelled to ascribe utility to all characters, and can explain useful and use- less characters by reference to the same facts of organic diversity and association in species. SUMMARY OF EVOLUTION THEORIES. Static theories view the species as normally stationary, and ascribe evolutionary motion to environmental causes of adapta- tion. The static theory commonly called Darwinism (though avoided by Darwin himself) treats adaptations as caused indi- rectly through natural selection, by the survival of the fittest of the individual variations. The static theory of Lamarckism treats adaptations as direct results or responses to environmental influences. Saltatory theories view the species as normally stationary except for rare intervals of sudden transformation or " muta- tion " caused either by the environment or by internal "forces" 306 cook of unknown character. Selection can determine the survival of mutations adapted to environmental conditions, but exerts no direct adaptive influence. Determinant theories view species as moving gradually in definite directions in obedience to internal " principles of per- fection " or "mechanisms of descent." Adaptation depends on the coincidence between evolution and environment ; selec- tion exerts no direct influence. Kinetic theories view species as normally in motion, but not in a single or definite direction, and not as a result of environ- mental causes. The normal evolutionary motion of the species may be restricted and deflected by the selective action of the environment, resulting in adaptation. The adjacent tables may assist in showing the relations be- tween these different types of evolutionary theories. Table I indicates the methods by which the various doctrines answer some of the principal questions regarding evolutionary motion. Table II brings these questions into relation with the conclu- sions reached in previous chapters. Discrepancies between dif- ferent evolutionary doctrines are often explainable by the fact that some of them are in reality theories of adaptation or of speciation, rather than of evolution. Thus, as the table shows, interbreeding is a strongly negative factor in the multiplication of species (speciation), but at the same time it is a strongly posi- tive factor in evolution. The chief factors in adaptation and speciation have only negative or restrictive effects upon evolution. NORMAL CONDITION OF SPECIES. The most fundamental diversity of opinion regarding the nature of evolutionary motion is that of the normal condition of species. Two assumptions are possible and have equal warrant for scientific consideration. Under theories of environmental and selective causation, it has been taken for granted that species are normally stationary and uniform unless acted upon by some disturbing external influence. The question of causes, on this assumption, is a simple one. The difficult problem is to explain how the external influences produce the organic results which have been ascribed to them. Fifty years of study have been ASPECTS OF KINETIC EVOLUTION 307 S m o 0 to "0 3 rt ii C .Q 0 si C >■» u O 7D « U a Oh - --' £ «.„- = SI 5 s$>a ■5 ^ E E e >> •C a ?i P o ^ £ O £ 3 *3 3 rt ol — 3 u- — — CD e O.O 3 r •- ~ E X c S.2 53 c£ W Q « J; o P-g <« E "5 c fe 3 2 ° •§ SI o •3 c Ph W CO — •"" 3 h <-! — ! I •J It! « O )— 1 c 1— 1 eS C cS c 3. .5 2S O <-> T. a* 3 *H — J3 S ho o * £ «>^ «j «s >sa > .ft v. ,"•• ^ CO «2 «9 .ft < 0 ho 0 to 0 Oh w 1? O H Q c 0 > ft u > O 0 a .•a 1 to ho (0 0 Oh « < z z H 1) --. S 0 M.2 « u ft i-l i-i B "> .ft O > ■3 co .■v. 0 Oh 5, C c .2 3 a. O « > T3 a. w < C/3 308 cook expended on this phase of the problem, but with no direct results. For this reason, if for no other, the careful consideration of the alternative possibility would be justified. The kinetic theory is not dependent, however, upon merely abstract or inferential justification, but is supported by the evi- dence of all observations and experiments which have a bear- ing upon the question. That groups of organic individuals become different whenever they have been isolated for any con- siderable periods of time, may be taken as proof that evolutionary change is a general and normal condition of the existence of species. It can be asserted, of course, that divergences be- tween groups of common origin are due to differences of environment, but the inadequacy of this explanation is con- clusively shown by the many instances where groups have pre- served great similarity of habits and environmental conditions, but have attained, nevertheless, to a great diversity of form and structure, as in the conspicuous instance of the animals of the class Diplopoda, and of various classes of the lower plants, such as the mosses and hepaticae. Two modifications of the stationary assumption had been formulated, previous to the kinetic theory. Under the muta- tion theory of Professor De Vries, the normal condition of uni- formity is supposed to give place at rare intervals to periods of mutation or sudden appearance of new species. In the deter- minant theory of Nageli, species were held to be normally in motion, but the motion was supposed to follow a definite direc- tion as the result of internal physical and chemical adjustments. The changes predicated as normal for species under the kinetic theory are of an indeterminate and composite character. The species is not thought of as changing in one direction merely, but in many characters at once, the required result being a con- structive coordination of changes which will increase the vita efficiency of the organism and enlarge its power of utilizing its environmental opportunities. RAPIDITY OF EVOLUTIONARY MOTION. Static theories, which have agreed in thinking of species as normally stationary, have also taken it for granted that evolu- ASPECTS OF KINETIC EVOLUTION 3O9 tionary changes must be gradual, and some writers have dwelt upon the imperceptible slowness of evolutionary progress. The mutation theory of Professor De Vries adopts the other extreme, in holding that evolutionary motion is abruptly discontinuons, the individual organism leaping, as it were, from one species to another without any steps or gradations. From the kinetic standpoint, mutations like those studied by Professor De Vries are interpreted as abnormal and degenerative phenomena, but the fact is recognized that the individuals of many species in nature have very recognized differences, so that the steps of evolutionary progress may not always be infinitesimally grad- ual. There are indications that prepotent new characters may often transform a species or variety in a comparatively short period of time. CONTINUITY OF EVOLUTIONARY MOTION. Theories which ascribe organic changes to selection or to en- vironmental causes imply that progress is limited to the charac- ters which happen at the time to have environmental significance. In this view evolutionary motion, though gradual, must be de- scribed as occasional, rather than as continuous. After a period of selective development a species might cease, for a time, to be affected by selection and remain stationary, or might even retrograde, as claimed by Weismann and others. In the mutation theory the idea of occasional change is car- ried still farther, so that evolutionary motion would need to be described as intermittent and occurring only at rare intervals. This is the type of evolutionary theory which comes nearest to the older doctrine of separate creation of species. It represents species as arising from single individuals, and denies gradual or continuous progress. It declares that evolutionary motion is saltatory or discontinuous ; that there are sudden changes or jumps from one species into another. Such an evolution could not be described as taking place in species, but between them, the species themselves being essentially stationary except when acted upon by special " forces." Whether the forces are exter- nal or internal is a matter of opinion which subdivides saltatory evolutionists into two subordinate schools. 3io COOK Saltatory evolution consists of a series of abrupt lateral dis- placements, each species remaining stationary and unchanged from the time of its origin by mutation. No forward progress of the members of interbreeding groups is provided. Mo- tion takes place only in the individuals which give rise to the new groups. Selection would thus have no influence upon evo- lutionary motion in connection with the mutation theory. Its function would be limited to the determination of the survival of the new species which might prove to be adapted to their environments. Motion is conceived only in simple inflexible lines and not in a network of descent which can bend in adap- tive directions when environmental obstacles are encountered. Saltatory theorists do not deny that diversity exists among the members of species, but they ascribe this to the influence of external conditions or to a general principle of inconstancy or fluctuation, without any special evolutionary significance. Saltatory theories stand in most direct contrast with those which ascribe continuity to the evolutionary motion of species, which are thought of not as advancing by leaps or sudden trans- formation of one species into another, but as going forward by gradual steps, larger or smaller. Natural selection by the en- vironment is thought of as changing the average and hence as causing evolutionary motion. The higher groups of plants and animals have so many adaptive characters that evolution by natural selection has been accepted by many biologists as a demonstrated fact. Determinant and kinetic theories agree in expecting evolu- tion to be continuous, the one because the internal mechanisms would continue to act, the other because the interbreeding of the ever-diverse individuals of the species is being continued. MUTATIONS DISTINGUISHED FROM NATURAL SPECIES. There is a wide and fundamental difference between the kind of evolutionary motion shown by mutations of inbred domesticated species and that by which the progressive development of natural species has been brought about. The condition of in- breeding under which mutations appear has so far weakened the organism that the newly modified form is recessive, that is, ASPECTS OF KINETIC EVOLUTION 3 I I it tends to disappear when crossed with unrelated groups. Such variations could not spread or propagate themselves in a nor- mally symbasic species ; each would need to be carefully iso- lated in order to be preserved. In the second place, very few, if any, of the thousands of mutations which have come under the eyes of planters and experimenters have proved to be more fertile, in the true reproductive sense, than the parental types. Nearly all of them are conspicuously deficient in this respect, and would thus struggle under a fatal selective handicap in competing with the parent form, if they were not at once wiped out by interbreeding. Mutations have very great agricultural importance, but their practical value will not be enhanced by overlooking this fact of deficient fertility which is fatal to the view that they represent a genuine condition of progressive evolution. Mutations arise sideways, as Professor De Vries explains, but it does not follow that new species are formed in this manner. Mutations are frequent in domesticated plants because varieties in cultivation are separated by inbreeding from the normal forward progress of the whole interbreeding species. Each species when once formed is supposed, under the mutation theory, to remain stationary so that progress can be made only when new varieties become segregated from the mass. There is, however, another and very different way in which variations can contribute to evolutionary progress. Instead of being recessive mutations, the variations which have practical evolutionary significance are prepotent, and can work one change after another in the gradually advancing group. The true evo- lutionary significance of mutations is not that species arise by mutation, but that the progressive steps, by which the evolution of species is gradually accomplished, are not imperceptibly small. There may be a very appreciable advance between two successive individuals. Very acute selection or some other way of separating a new mutation from its unmodified parent stock must be imagined in order to account for its preservation, but plants and animals abound in characters which could scarcely have been perpetu- ated in this way. With self-fertilized plants a single individual Proc. Wash. Acad. Sci., January, 1907. 312 COOK can start a new race or variety, but with sexually differentiated animals this is much more difficult, since interbreeding is neces- sary for reproduction. An actual instance will illustrate the point. In all the millipedes of the world-wide order Merocheta the olfactory cones of the antennae are four in number, arranged in a square, with the single exception of a series of closely related East African genera of the family Gomphodesmidae,1 which are unique in the possession of ten olfactory cones arranged in a circle. That the four cones in a square is the ancestral condition, is certain, because it is shared also by all the other orders of the very ancient class. Diplopoda, many members of which are known from the carboniferous period. That the number is invariable in the order Merocheta can not be claimed, since, obviously, it must have varied at least once, when the circle of ten cones came into existence. No variation has been recorded, however, either in the four-coned or the ten- coned genera, on the many thousands of specimens which have been examined. Nor are there any indications that the ten-coned condition is an advantage which has gained any favors from natural or other forms of selection. The ten-coned genera as a group show no other conspicuous peculiarity and have contributed, apparently, only m average share to the evolutionary diversification and geographical distribution of the family. Moreover, the habits and environmental relations of the whole class Diplopoda are such as to reduce the influence of natural selection to a minimum.2 Under such circumstances the sidewise origination and pres- ervation of a ten-coned new species as a mutation seems highly improbable, but there is, on the other hand, no reason why a genetic variation to ten cones should not spread through a species and be carried forward into the other species and genera into which the ten-coned group might afterward subdivide. If there had ever been millipedes with the intervening number of 1 Cook, O. F., 1899. African Diplopoda of the Family Gomphodesmidae. Proc. U. S. National Museum. 21 : 677-739. 2 Cook, O. F., 1902. Evolutionary Inferences from the Diplopoda. Proc. Entomological Society of Washington. 5 : 14. ASPECTS OF KINETIC EVOLUTION 3 1 3 cones we have every reason to expect that indications of them would remain, either in species with such numbers or in occa- sional individual variations. The facts of mutation may help us to be reconciled to the probability that millipedes with five, six, seven, eight or nine cones may never have existed, but they do not warrant the general inference that evolution goes for- ward by the origination of species sideways by mutation. The difficulty is not that the mutations of domesticated plants and animals are not as different and as readily to be described and distinguished from each other as natural species. Nor is it impossible that some of the species named and described in formal botanical and zoological classifications represent mutative variations from narrowly segregated wild types. The differ- ences are not formal or theoretical, but physiological and prac- tical. The conditions under which the mutations of cultivated plants and animals arise are not those under which the construc- tive evolution of nature has gone forward, and the mutations are deficient in the primary requirements of vigor and fertility. That discontinuous variations may contribute to the evolu- tionary progress of species in nature is no part of the mutation theory of De Vries, which definitely rejects and denies an)' grad- ual evolution, any continuous change and accumulation of char- acters. Species once formed by mutation are just as stationary and immutable, according to De Vries, as Linnaeus said they were. All the evidences of gradual evolutionary divergence of organic groups accumulated by Darwin and his successors are ignored in the mutation theory, because no evolutionary changes were detected in the original CEnotheras which Professor De Vries kept in his garden for eighteen years. The kinetic theory is not thus at odds with the facts of science. It provides an evolution of species by a thor- oughly gradual, continuous process, more broadly continu- ous, indeed, than any suggested before. It recognizes that new variations are prepotent, and are able to accumulate and to transform the species in which they appear. Species are nor- mally in motion and do not depend upon the intermittent inter- ference of selection, nor upon mutation, for the development of new characters. Instead of finding the motive power or 314 COOK active principle of evolution in natural selection or in mutation, the kinetic theory finds evolutionary causes in normal diversity and free interbreeding in specific networks of descent. Both the selection theory and the mutation theory imply that new characters and new types have to be preserved by isolation. Under the kinetic theory it is clearly perceived that isolation explains only the multiplication of species, but is not an evolu- tionary factor, or even a necessary condition of evolution. The kinetic theory provides for the first time a consistent outline of a method of gradual and continuous evolution in normally ex- tensive, freely interbreeding specific groups, the condition in which organisms everywhere exist in nature. PRINCIPAL AGENT OF EVOLUTIONARY CHANGE. At this point the various theories show, perhaps, their most obvious divergencies. The doctrine of pure selection, or Dar- winism, holds that selection is the actual cause or principle of evolutionary advance, supporting this by various other assump- tions, such as an environmental causation of variations or a cor- relation between useful and useless variations.1 The isolation theory of Gulick appreciates the inadequacy of selection and seeks for special conditions or behavior which can explain the evolutionary progress of groups of individuals which have merely been isolated from the parent species with- out having been placed in appreciably different environments. The Lamarckian doctrine of direct adaptation finds its greatest ad- vantage here, in that the environment itself is supposed to cause the changes directly. Professor De Vries argues, in some of his writings, that mutations are due to environmental causes, though frankly admitting that the connection of events is unknown. 1 Belief in correlation of characters as an important adjunct to selective evo- lution has been reaffirmed very recently by Professor Lank ester. "For they [correlated characters] enable us to understand how it is that specific characters, those seen and noted on the surface by systematists, are not adaptations of selective value. They also open a wide vista of incipient and useless developments which may suddenly, in their turn, be seized upon by ever, watchful natural selection and raised to a high pitch of growth and function." See Lankester, E. Ray, 1906. Inaugural Address before the British Association for the Advancement of Science. Science, N. S., 24: 228. ASPECTS OF KINETIC EVOLUTION 3 I 5 It is commonly taken for granted by the advocates of the selection hypothesis that a certain constant of variation will be maintained by the species, so that the cutting off of the extremes on one side will cause a still greater development on the other, and thus actually move the species along. This idea may never have been very definitely formulated, but it is obvious that many writers on selection have relied upon the unexpressed assumption as affording the means by which selection could produce evolutionary change in a normally stationary group of organisms. The Darwinian doctrine of variation grafted upon the older idea of stationary species resulted in the conception of a species composed of variable individuals, but with a stationary specific average. Experiments with domesticated varieties had shown that selection could change the center of gravity or character- average of a group, and this idea applied to nature at large gave the hypothesis of evolution through selection. In arguing the inadequacy of selection, Mivart, De Vries and others have taken the ground that selection could not carry the specific average beyond the boundary or limit of range of variation for the original group, and this is the logically correct inference, unless the idea of a constant of variability be included as a factor of the problem. But even this is inadequate to account for the general evolutionary results, for unless the further notion of a normal tendency to progressive change be added, the presumption would be that the selectively reduced species would attempt merely to reproduce its lost members, to regain its original size and cover again the field from which it has been excluded by selection. It may be held, therefore, that both in logic and in fact the explanation of the ascertained and generally admitted data of selection depends upon the recognition of a normal and spon- taneous tendency of species to evolutionary change. It is this tendency, this specific kinesis or law of motion, which carries species into close selective contacts with their environments. The species are travelling by their own motion, in spite of selective obstacles, and not because environmental selection is carrying them along. 3 16 cook The determinant theory of Nageli, as already indicated, ascribed changes to an internal "principle of perfection" of heredity, which conducted the evolution of a species in a definite direction. There was no need, in this view, of showing any direct connection with the environment. Selection was applied to a species as a whole, to preserve or to eliminate, but it was not thought of as actuating evolution or as conducting it in adaptive directions. The determinant theories of Weismann and his followers may be described as hybrids between the doctrines of Nageli and those of Darwin and Lamarck. They predicated a cel- lular mechanism of heredity for conducting the process of evolution, but supposed that this mechanism could be actuated or affected by environmental influences and compelled in this way to carry the species in directions of adaptation. Darwin, in his theory of pangenesis, assumed that all parts of the body of the parent contribute materials to the germ-cells and hoped thus to explain how characters acquired from the environment might be passed on to succeeding generations. Weismann denied the inheritance of acquired characters, but he nevertheless repeated Darwin's attempt at providing for the inheritance of environmental influences, because it appeared impossible without this to construct a theory of environmental causation and explain the facts of selection and adaptation. Weismann was well aware that his theory of determinants was so complex as to appear improbable, but he defended it with persistence on the ground that it was the only way in which heredity could be understood. Unfortunately, the vast complexity of ideas does not explain the facts of organic descent, but only adds to them an even more mysterious hypothetical field. Moreover, the data of environmental relations do not accord any better with the Weismannian than with the Dar- winian hypothesis. Experiments have not shown that there is any close, constant or definite relations between environment and heredity. The most that can be claimed is that the environ- ment, in some manner still quite unexplained, may sometimes induce an instability, or tendency to stumble and fall from the normal hereditary pathway of the type. ASPECTS OF KINETIC EVOLUTION 3 17 The theory of determinants afforded, at most, a method of thinking about the process of organic succession, but it does not appear that this way of thinking is either correct or neces- sary. It assumes a complete diversity of nature between ger- minal and somatic cells, which the facts do not warrant, especi- ally among plants, and it assumes further that there are definite mechanical directive relations between the germ-cells and the resulting organisms, which the facts also refuse to indicate. Of the real nature of heredity we know, as yet, absolutely nothing, any more than of analogous phenomena, instinct and memory. Speculations, even of purely hypothetical character, may some- times be of service in the treatment of scientific problems, but no speculation should be cherished which hides or even casts a shadow over facts. Under kinetic evolution the symbasic interbreeding of the diverse individuals of the species is held to be the principal agent of evolutionary change, since it is in this manner that the prepotent variations which appear among the component indi- viduals are transmitted and combined into the complex organic result. Interbreeding is held to effect an integration of indi vidual variations inside the species, instead of each variation being considered a new species, as in the mutation theory. Symbasis is one of the general conditions of organic exist ence, but under static theories its evolutionary significance was so completely overlooked that no term was provided by which it could be directly and definitely symbolized. The word in- terbreeding, if used alone, would generally be misunderstood in one of two opposite and equally unfortunate senses. Some writers use interbreeding as synonymous with inbreeding or close-breeding, and some for wide cross-breeding, which are exactly the conditions to be avoided in the discussion of normal specific relations. Another term being indispensable, symbasis was introduced, in allusion to the fact that the individual mem- bers of species are normally associated in groups. The expres- sion also lends itself most conveniently to the description of kinetic interpretations, in view of the fact that the association of organisms into symbasic groups is looked upon as one of the principal agencies of evolutionary progress. 318 cook The introduction of a new term is always to be deprecated, and may help very little, after all, in the explanation of a new distinction. The word has to be explained, as well as the idea. Nevertheless, there are occasions like the present, where progress in expression is likely to be permanently hampered unless we can be permitted to place definite labels upon our phenomena and refer to them by unequivocal word-symbols. Symbasis, more properly than any other ascertained fact, can be called a cause of evolution. It may not cause variation, but it does enable variations to be combined into a general evolutionary change of type. UTILITY OF NEW CHARACTERS. New characters, as mere fortuitous variations, might or might not be useful, but if selection were the only cause of evolution, progress would be limited to characters of definite utility. Every character, therefore, which has attained to any consider- able degree of expression would have a definite use, or would have had use at some former time in the evolution of the species. This logical necessity of predicating the utility of all characters is the most obvious weakness of the theory of selec- tion, for there are large numbers of character differences be- tween species which are not only obviously useless at present but which were probably equally useless in the past. Gulick's isolation theory does not insist on the utility of specific differences, nor do the mutations of De Vries or the de- terminate changes of Nageli and Weismann follow, of neces- sity, the course of environmental utility. Selection would explain the disappearance of types too far lacking in fitness, but adaptation would remain a mere coincidence, depending on whether adaptive variations happen to appear. Under the kinetic theory it is possible to admit that useful and useless characters have equal possibilities of appearing and evolving, as long as they do not become actually detrimental, but at the same time selection is admitted to have a definite and practical evolutionary function, since the rejection of harmful tendencies has the power of enforcing more rapid specialization in useful directions. Selection is, indeed, more effective for ASPECTS OF KINETIC EVOLUTION 3 19 inducing adaptation under the kinetic theory than under the purely selective doctrine of Darwinism, because in kinetic evo- lution a much wider range of characters can be expected to reach a sufficient development to render them of selective im- portance. Under a logical static theory, only those characters could be developed which have selective value from their first inception. METHODS OF PRESERVING NEW CHARACTERS. The great weight given to the various forms of selection, isolation, and environmental influence as factors of evolution have been determined largely by the belief that new characters or variations could not be preserved unless they were in some way separated from the unmodified parental type. This opinion has been supported largely by the fact that many of the varia- tions which have been taken for examples of normal evolution- ary motion have been in reality more or less abnormal results of the condition of inbreeding common in our domesticated varieties of plants and animals. The prepotency of the un- selected wild type has been insisted upon, as well as the swamp- ing effects of intercrossing, when the characters of the carefully selected variety fade away into those of the unspecialized parental form without leaving any apparent result. Neverthe- less, the fact seems to be that new characters are prepotent, not of necessity over the whole taxonomic species to which the individual may belong, but at least in the particular variety or group and in the particular stage of interbreeding in which the variation appears. The recognition of the prepotency of new variations makes it obvious that the preservation and continued evolution of new characters does not involve the necessity of isolating the new form or the extinction of the old, after a period of struggle for existence. Mechanical theories of evolution have centered largely about this question of acquiring characters, but it is still more impor- tant to know how characters are preserved after having been acquired. Organisms appear to acquire some characters from the environment, but it does not follow that the characters are also preserved by the environment, or even that the characters 320 COOK acquired from the environment are those which contribute in a definite manner to evolution. The kinetic interpretation en- ables us to understand the probability that a character is pre- served for the same reason for which it appears in the first place. The name Darwinism is commonly, though rather unjustly, limited to the gradual or selective theory under which variations gained genetic significance only when they were favored by partial or complete isolation, brought about either by the elim- ination of the less efficient parental form during the struggle for existence, or through geographical or other accidents prevent- ing the swamping effects of intercrossing. This meant that variations did not tend to be preserved, that they tended only to continue their fluctuations around the stationary specific average. This conception was based, as already indicated, on the choice of the fluctuating variations or unspecialized het- erism and artism as representing the variations on which evolu- tion proceeds. Under the assumption that organisms are normally stationary it was natural to ascribe variations to new conditions. It may be found, however, that the facts can be accommodated as well or better by supposing that new conditions of nutrition and growth afford more facilities for variation. Variations, once produced, tend to repeat themselves ; not, it may be, in all of the offspring, but at least in some of them. The object of varia- tions, the value of variations for the species, lies not so much in giving them new characters as in giving them a diversity of characters. Variations which appear in a part of the offspring, but not in all, serve most efficiently the purposes of increasing and maintaining heterism, and of insuring diversity of descent, after the manner of the many secondary sexual characters which appear to be quite useless except for this physiological purpose. The kinetic theory differs from all its predecessors in recog- nizing physiological reasons for holding that new characters are prepotent. From the fact that they afford opportunity for organic readjustment, they enjoy an advantage over the un- modified type both in accentuation of characters and in vitality and fecundity of offspring. The evolutionary possibilities of a ASPECTS OF KINETIC EVOLUTION 321 new character may depend as much or more upon its fitting into and supplementing the complex of existing characters as upon any direct utility from the environmental standpoint. Evolution, in other words, may be viewed as an aspect of the physiological process of interbreeding by which the vitality of organisms is sustained. NATURAL SELECTION AS AN EVOLUTIONARY FACTOR. The preponderance attained by the selection theory has prob- ably been due, in large measure, to its logical simplicity and consistency in holding that selection is the positive, efficient factor or actuating principle of evolution. The unbiological public has accepted this interpretation of the causes of evo- lutionary motion with practical unanimity, but among biologists themselves there has always been a wide appreciation that the facts did not warrant the definite generalization which Darwin himself carefully avoided, but which his friends made for him and christened with his name. All other suggestions of methods of evolution are the result of more or less definite perceptions of the inadequacy of natural selection as an evolutionary cause. No amendment of natural selection has the logical consistency of the original, nor has any gained a comparable popularity in the scientific world. The mistake has been made, if the present diagnosis is correct, in attempting to modify or repair the hypothesis of selection as an evolutionary cause. Under the kinetic theory selection appears as a negative fac- tor only ; its power is to inhibit motion, not to cause it. It is not improbable that selection, by closing other avenues of change, can induce more rapid progress in a particular direction, but such an effect of accleration would not prove that selection can cause evolutionary motion ; it would indicate that a certain amount of change necessarily takes place as the result of causes inherent in the species. A variation eliminated by selection does not help to maintain the needful diversity of descent, and this may make the surviving variations the more effective for inducing adaptive specializations. Selection, by thus restricting the field of change, may be able to focus the evolution upon one 32 2 COOK variation, but a condenser is not to be reckoned as a source of light. The kinetic theory therefore definitely abandons selection as a cause or positive factor, and perceives that the influence of selection, powerful though it be in many cases, is of a negative and restrictive character — an influence which could not be exerted if the species were not already in motion. The kinetic theory, though departing radically from the doctrine of selection as an evolutionary cause, is, in a practical sense, much nearer to Darwinism than are many other sug- gestions which, though intended to supplement the selection hypothesis, would in reality completely nullify it, by denying to selection any true power to influence the course of evolutionary progress. The kinetic theory, though denying that selection is in any proper sense an evolutionary cause, ascribes to it a definite evolutionary function. The environment does not carry the species into adaptive specialization, it only deflects the normal specific motion. The evolution is in the species, the power of deflection in the environment. Professor De Vries clearly recognizes that the function of selection is regulative and not active, though he still refers to it as a cause of evolution. " Notwithstanding all these apparently unsurmountable diffi- culties, Darwin discovered the great principle which rules the evolution of organisms. It is the principle of natural selection. It is the sifting out of all organisms of minor worth through the struggle for life. It is only a sieve, and not a force of nature, no direct cause of improvement, as many of Darwin's adver- saries, and unfortunately many of his followers also, have so often asserted. It is only a sieve, which decides which is to live, and what is to die. But evolutionary lines are of great length, and the evolution of a flower, or of an insectivorous plant is a way with many sidepaths. It is the sieve that keeps evolution on the main line, killing all, or nearly all that try to go in other directions. By this means natural selection is the one directing cause of the broad lines of evolution. " " Of course, with the single steps of evolution it has nothing to do. Only after the step has been taken, the sieve acts, elimi- ASPECTS OF KINETIC EVOLUTION 323 nating the unfit. The problem, as to how the individual steps are brought about, is quite another side of the question."1 This is in notable contrast with the previously quoted dictum of Professor Lankester, regarding an " ever-watchful natural selection " by which characters are " seized upon " and " raised to a high pitch of growth and function." INTERBREEDING AS AN EVOLUTIONARY FACTOR. In full accord with the idea that evolutionary change or motion is caused by selection or environmental influence, are the opin- ions, already emphasized, that isolation is necessary to preserve new characters, and that the sexual phenomena of interbreeding stand in the way of evolutionary progress by hindering the per- petuation of new characters. These corollaries of the selection hypothesis find no place in the kinetic theory. Interbreed- ing and other phenomena of sexuality have been reckoned in the present discussion as positive factors in evolutionary motion. Evolution, in the kinetic interpretation, represents the work- ings of no special force, principle or mechanism ; it is carried forward by the symbasic interbreeding of the diverse individuals of which species are composed. The final and ultimate expla- nation of evolution must await an understanding of the constitu- tion of living matter. We must learn why the prepotent genetic variations occur, and why the interbreeding is necessary. But having once appreciated the variations and the interbreeding as ever-present facts, evolution is no longer mysterious ; it follows as a natural and obvious consequence. THE KINETIC FIGURE OF EVOLUNTIONARY MOTION. It will be apparent from the preceding chapters that the evo- lutionary motion predicated under the kinetic theory differs from that of previous doctrines in important respects. In the first place, it is a highly complex or compound motion instead of a simple one, not to be typified by a push from the environ- ment, by a pull by natural selection, by an occasional mutative leap, nor even by the onward transportation of a determining "DeVries, H., 1905. Species and Varieties, p. 6. 324 COOK " hereditary mechanism." The figure of developmental progress under the kinetic theory is that of the advance of a huge and intricate network or trestle, built and supported by the inter- grafting of the lines of descent throughout the species. Envi- ronmental obstacles can compel the progressive advance of this specific structure to be accomplished by many lateral bendings, but these deviations and displacements need no longer be mis- taken for examples of normal evolutionary motion. That indi- vidual organisms can step aside, or even fall out of the ranks, proves, at the most, only that such transverse motions are pos- sible ; it does not show that they represent the method or the conditions by which the constructive evolutions of natural species go forward. The environmental reactions and mutations are made suddenly and can be readily demonstrated to our impa- tient eyes, but the coherent advance of the whole specific net- work has to be inferred from the relations of species as we find them in nature. Some are inclined to distrust the results of the cosmic labora tory and to prefer to explain evolution by the lateral diversions which can be demonstrated in their own experimental cages and gardens. After keeping Lamarck's evening primroses in his garden for eighteen years without detecting any change, Professor De Vries has concluded that the species is constant and stationary and that further evolution is accomplished only by mutative variations, like those which appeared during this interval. "There is neither a gradual modification nor a common change of all the individuals. On the contrary, the main group remains wholly unaffected by the production of new species. After eighteen years it is absolutely the same as at the beginning, and even the same as is found elsewhere in localities where no mutability has been observed. It neither disappears nor dies out, nor is it ever diminished or changed in the slightest degree. ..." My evening primrose, however, produces in the same locality, and at the same time, from the same group of plants, quite a number of new forms, diverging from their prototype in different directions. ASPECTS OF KINETIC EVOLUTION 325 "Thence we must conclude that new species are produced sideways by other forms, and that this change only affects the product, and not the producer. The same original form can in this way give birth to numerous others, and this single fact at once gives an explanation of all those cases in which species comprise numbers of subspecies, or genera large series of nearly allied forms."1 These inferences were made, of course, without reference to the kinetic conception of evolutionary motion as a specific struc- ture or network of descent. Nor is the possibility considered that a small group of individuals isolated and inbred in a foreign land might behave in an abnormal manner, or at least in a manner that would afford small indication of the normal mode of evolutionary motion. Other parallel cases observed in coffee, cotton, capsicum, tea and other plants, indicate that mutative variations like those of the evening primrose are the regular re- sults of the treatment to which the plants have been subjected in domestication. Instead of illustrating the method by which evolutionary advance is accomplished, mutations appear to represent a stage in the degeneration of organisms which have been removed from the vital fabric of specific descent ; they do not show how the evolutionary network is woven, but how the strands can be unraveled. Conditions of uniformity like those of inbred domesticated varieties are to be found in nature only exceptionally, in the relatively few degenerating types which have become regularly addicted to self-fertilization or to vege- tative propagation. Nor do we find under normal evolutionary conditions of symbasic interbreeding and individual diversity these violent mutative departures from the parental types. There is a vastly greater range and flexibility of characters and character-combinations. Nevertheless, it is very doubtful whether a species as a whole would make an appreciable evo- lutionary advance in eighteen years. In any event, the fact could hardly be determined from a few specimens in a foreign garden. All kinds of variations can be described as having been pro- 1 De Vries, H., 1905. The Evidence of Evolution. Smithsonian Report for 1904, p. 396. 326 COOK duced sideways. The doctrine of selection, like that of muta- tion, looks upon lateral or transverse displacements as the steps by which evolution is accomplished. From the kinetic stand- point it appears obvious that only those lateral movements really contribute to the evolution of the species which make a lasting addition to the internal diversity of the species and broaden and strengthen the structural network of descent. Mutations which arise under conditions of inbreeding do not serve this purpose. They are loose loups or free ends of the fabric of descent, torn out by the disarrangement of the tensions of the specific machinery of development. They do not affect the species, of course, if they remain isolated from it. On the other hand, mutations which are allowed to interbreed freely with the wild type, or even with each other, loose their distinctive peculiarities and are merged back toward the ancestral form, and [toward the more normal condition of promiscuous individual diversity. As evolutionary phenomena the mutations described by Pro- fessor De Vries have not less of interest and significance than the facts of adaptation and environmental adjustment which served as the basis of earlier theories of evolution. And like the data of the earlier theories, the facts of mutation are capable of being interpreted in a very different relation to the evolution- ary motion of specific groups of organisms. Since constructive evolution is accomplished, as far as we know, only in these large groups of freely interbreeding individuals, we may well be cautious in the acceptance of any doctrines which do not take into account the normal constitution of species, and the nature of the motion by which their evolutionary progress is accomplished. A species is not a merely arbitrary collection or aggregate of organisms ; it is itself an organization by which organic exist- ence is maintained and organic evolution is accomplished. It is customary to think of the higher types of organisms as hav- ing been made possible by the association of greater and greater numbers of cells, but this association and specialization of cells into tissues and organs has not been accomplished without the meeting of another evolutionary requirement, the association of the organisms into large interbreeding groups, or species. ASPECTS OF KINETIC EVOLUTION 327 Organic energy is primarily an integration of cellular energy, and the energy of cellular development has to be readjusted and renewed by conjugations between cells of diverse descent. The answer to the question why this is so must come from a new department of science, a general cellular biology which shall study the problems of cellular organization and associa- tion. It is here, if anywhere, that we must learn why organisms are normally diverse, why interbreeding is necessary and why evolution follows as a universal consequence. A species, viewed as a protoplasmic fabric of interwoven lines of descent, is different from any other object in nature, but its properties and potentialities are no less peculiar than its structure and its modes of motion. 5. THE HEREDITY CONCEPT MODIFIED BY HETERISM. Questions are debated with the most persistence and the least profit when diverse opinions are being expressed by means of the same words. The term heredity has figured largely in evo- lutionary discussions ever since the time of Darwin, and yet the ideas which it represents are by no means the same in the minds of the many investigators who use it. The meanings do not vary merely in the extent of their application to related ideas. They differ fundamentally in their standpoints, and in their conceptions of the nature of the causes of evolution. The traditional concept of heredity, the supposed production of like by like, also enters largely into the composition of the various philosophical systems of evolution, so largely, in fact, that evolution, descent and heredity are often treated as synony- mous terms. Indeed, the whole subject of evolution is often summarized and crystallized into heredity, so that no further thinking is possible which does not definitely adopt or as defi- nitely reject the heredity conceptions of the various schools of evolutionary study. The extreme views are very widely diver- gent, and perhaps equally remote from the truth. On the one side is the hypothesis of environmental causation, or a direct impression or moulding of characters by external conditions ; on the other side is the hypothesis of prefiguration or definite predetermination of characters by internal character- Proc. Wash. Acad. Sci., February, 1907. 328 COOK unit mechanisms of descent. Some regard heredity as a sum- mary of environmental influences, and some as the result of an intracellular mechanism of predetermination, having no relation to the environment. The environment does not form organisms, but neither can organisms be thought of correctly without bearing in mind their normal diversities and powers of individual accommodation to different external conditions, powers which are as incompatible with ideas of complete predetermination from within as they are with ideas of direct causation from without. Heredity, as signi- fying the succession of organisms in continuous lines of descent, is an actual fact, though as yet quite unexplained. Heredity, in the sense of a normal uniformity of organisms in species, does not exist. Instead of like producing like, the rule of hered- ity is that unlike produces unlike. To assist in an understand- ing of evolution and of the processes of descent the conception of heredity must be modified, and for some purposes entirely replaced, by a recognition of the facts of heterism, the normal inherent diversity shown by the individuals, castes and sexes of the same species. It is only when the members of a species are compared with the members of other species that they can be said to be alike. Compared with the members of their own species, all organisms are different. Heredity and variation are not uncommonly personified as two opposing agents or " forces," the one striving to make organ- isms alike, the other to make them different. The late Pro- fessor Hyatt and others have even gone so far as to definitely locate all the heredity inside the organism and all the variation outside, holding that the organisms would be identical in form and structure were it not for variable external influences. The conception of heredity as an ideal uniformity is more applicable to some species than to others, but is not completely true of any. Experiment has everywhere shown that the members of the species and varieties are alike — as far as they are alike — because they breed together, not because they live in the same environments or because their form is definitely predetermined by an internal mechanism. The network of descent is a part of the mechanism of heredity, quite as truly as any character- unit particles can be. ASPECTS OF KINETIC EVOLUTION 329 The character-unit hypothesis of heredity is one of the corol- laries of the environmental causation hypothesis of evolution. It seemed necessary to predicate 'something in addition to the observed methods and sequences of organic existence, in order to explain the evolutionary progress of species. How could the environment change the characters of organisms, and how could the changes of the characters be inherited and bring about the transformation of the characters of the species? These are the questions which Darwin sought to answer by his hypothesis of pangenesis, a migration of determinant particles from all parts of the body of the parent to the reproductive cells, so as to repeat in the offspring the modifications which the parent organ- ism had experienced. The doctrine of pangenesis never found any support or justification in fact, since it could not be as- certained that characters caused by the environment are in- herited by pangenesis or otherwise. Nevertheless, the doctrine of determinant character-unit particles has been kept alive by the speculations of Nageli, Weismann, and many other mathe- matically inclined students of evolutionary problems. The kinetic theory does not approach the problem from this standpoint, for it finds causes of evolution in the facts of sym- basic interbreeding and normal intraspeciric diversity. The first significant fact in the direction of an explanation of evolu- tion is the method of interweaving of the network of descent in which evolutionary progress is carried forward. In place of the assumption by static theories of a hypothetical mechanism of character-determination, with an equally hypothetical result of ideal uniformity, the kinetic theory presents for our study con- junctions of lines of diverse descent and results of continued diversity of offspring. HEREDITY IN CELL SPECIALIZATION. The fact that the germ-cells of the higher plants and animals are so different from those of which the various tissues and organs of the adult body are composed, has been taken to mean that they have some special function of heredity. A long series of exceedingly difficult and detailed investigations have been made in the hope of discovering these causes of development 330 COOK which were supposed to lie hidden inside the nuclei of the reproductive cells. If we trace back the organic series to their more simple repre- sentatives we not only find that the body cells become more like each other, but that the distinction between somatic or body cells and reproductive cells quite fades out. When the unicellular stage is reached, the problem of heredity seems largely eliminated, for here reproduction consists merely in the repeated division of cells into two equal parts, the close similarity of which appears in no way mysterious. The difference between the higher plants and animals and the lower lies in the fact that in the former the cells do not repeat indefinitely the same size, shape and structure, but are greatly diversified, though remaining joined together in colonies or compound individual organisms. Viewed in this manner it becomes apparent that there is no par- ticular point at which this mechanical idea of heredity becomes necessary, no definite stage where the similarity of parts of a divided cell ceases to explain the facts of organic structure. Reproduction and growth frequently figure merely as two names for the same process. Division of cells, which is repro- duction among the lowest organisms, means growth in the higher. The process of conjugation of cells commonly termed sexual reproduction, need not be allowed to complicate the question of heredity, since the same stages of gradual differ- entiation can be traced among double- or conjugate-celled organisms as among simple-celled. Organisms which have conjugated recently do not divide differently from those which have not, though they may not be able to continue to divide indefinitely without conjugation. Among the higher compound organisms, conjugation takes place only at the unicellular stage. All the cell divisions necessary to the building up of the plant or animal body must be carried on without any readjustments of conjugate relations. To this limitation is doubtless due the fact that as organisms increase in complexity and in special- ization of tissues, conjugation becomes a more and more indis- pensable preliminary to the reproduction of each new cell colony, or compound individual. If, for example, there could be one hundred divisions between each conjugation, this would ASPECTS OF KINETIC EVOLUTION 331 suffice for one hundred generations of unicellular organisms but might provide only one compound individual. Plants and lower animals can be grown from cuttings or will regenerate lost parts, but among the higher animals these powers of asexual reproduction gradually disappear. Divergence from the normal may occur at any stage in the development of the individual, which also varies continuously, and not merely in the germ-cell. If the life-history of a very simple animal or plant be considered, the concentration of in- terest on one point tends to disappear. The processes of growth and the preparation for spore-formation in such an organism as Spirogyra do not appear less interesting or less fundamental from the biological standpoint than conjugation and reproduc- tion. Moreover, we now know that adaptations arise inside of cells as well as outside. The chromosomes and centrosomes, no less than the larval stages of insects, may prove to be re- sultant phenomena of evolution, rather than causal or truly primitive. It is easy to understand how those who have approached evolution through the study of complex and specialized higher groups should be led to think of heredity as a mechanism, but if we take our standpoint at the other end of the organic crea- tion it becomes apparent that heredity is merely a name for the fact that cell divisions by which organisms are built up follow closely similar lines in each successive generation. Organisms are not different merely because they are built of different kinds of cells, nor merely by reason of different arrangements of the same kinds of cells. Both causes of difference are present together in all the higher groups. Both kinds of dif- ferentiation have gone forward simultaneously and it need not be thought more wonderful that the cells of the same compound individual are different than that different species should be found among unicellular organisms. Indeed, heredity is most perfect when the cells formed by successive divisions are all alike. It maybe deemed a departure from strict heredity when the)' become diversified, as in higher organisms. But whether the individual consists of a single cell or of a colony formed by many cell divisions, we are still dealing with the same 332 COOK fact of organic repetition, and have no more reason in the one case than in the other to view heredity as the function of any special organ. We may define heredity as the property of organisms with as much propriety as the chemist treats crystal- lization as a property of sugar. The cells know, as it were, how to arrange themselves repeatedly into similar colonies or compound individuals, just as the molecules of a chemical com- pound take repeatedly the same crystal form. The causes of crystallization and of heredity are equally unknown ; we can merely expect for the future that to which the past has accustomed us. We have no better reasons for expecting to find that the adult is definitely prefigured in the germ-cell that we have for supposing that the crystallographic forms or other properties of inorganic materials can be deter- mined by microscopical examinations of the substances in solu- tions or in amorphous states. The germ-cells with their chro- mosomes and other internal organs do indeed carry the organic sequence from one generation to another, but this fact gives us no warrant that they contain any parts or particles which will afford a general explanation of evolution. And even if the germ-cells do contain some feature of special bearing upon heredity, it does not alter the probability that the results of the agencies operating in the germ-cells are shown to best advantage in the completed organisms. Sperms and egg-cells are them- selves organisms, quite as truly as the elephants and whales, but their infinitesimal size, which kept them unknown and mys- terious so long, does not warrant us in ascribing to them any gratuitous mysteries, nor in failing to appreciate that evolution is a motion of the specific network of descent. Whatever the nature and functions of nuclear organs may be in different groups of animals and plants, we may expect that these organs and functions will find their primary explanation and relations in the evolutionary network of descent, rather than as affording an independent basis for theories of heredity. Neither the relations of individual organisms to environment, nor the possibility that germ-cells have predetermining relations to adults, will justify us in leaving out of account the network of descent in which the evolution of species goes forward. ASPECTS OF KINETIC EVOLUTION 333 HEREDITY AS A RESULT OF ENVIRONMENT. The strength of the predisposition toward theories of environ- mental causes of evolution finds many illustrations in the con- troversies which have raged about the Lamarckian doctrine of direct environmental influences. Thus Professor Lankester, even when opposing Lamarck, assumes environmental influ- ences of a character which the facts may not justify. It is shown that Lamarck was illogical in supposing that new environmental characters could be preserved by heredity and thus replace at once the effects of the " long-continued response to the earlier normal specific conditions," but it becomes evident, even while this excellent chronological distinction is being drawn, that it rests on a conception of heredity only slightly less objectionable than that of Lamarck himself. Though making no direct ref- erence to mechanical theories of heredity, these assumptions are such as to suggest and to justify such interpretations. " Normal conditions of environment have for many thousands of generations moulded the individuals of a given species of organism, and determined as each individual developed and grew ' responsive ' quantities in its parts (characters) ; yet, as Lamarck tells us, and as we know, there is in every individual born a potentiality which has not been extinguished. Change the normal conditions of the species in the case of a young indi- vidual taken to-day from the site where for thousands of gener- ations its ancestors have responded in a perfectly defined way to the normal and defined conditions of environment, reduce the daily or seasonal amount of solar radiation to which the indi- vidual is exposed ; or remove the aqueous vapor from the atmos- phere ; or alter the chemical composition of the pabulum access- ible ; or force the individual to previously unaccustomed muscular effort or to new pressures and strains ; and (as Lamarck bids us observe), in spite of all the long-continued response to the ear- lier normal specific conditions, the innate congenital potentiality shows itself. The individual under the new quantities of envir- oning agencies shows new responsive quantities in those parts of its structure concerned, new or acquired characters."1 lankester, E. Ray, 1906. Inaugural Address before the British Association for the Advancement of Science. Nature, 74 : 330. Science, N. S., 24 : 607. 334 cook If the environments controlled the character-units and thus moulded the characters of organisms we should expect to find that each environment would have its own organisms, or that all the individuals of the same species in the same environment would be alike, or at least more alike than individuals from different environments, but these results have not been attained. Sexual and other analogous differences which have been de- veloped among the members of the same species in the same environments are vastly greater than any of the diversities which differences of environments can cause or induce. More- over, there are nowhere in nature any constant environments which suppress or tend to extinguish the potential of adjustment. Vicissitudes are ever at hand, ready to make selections in direc- tions of adjustability. The highest types of organic life, those which have been able to travel farthest on the evolutionary road, are those which have responded most effectively to their oppor- tunities for learning the arts of adjustment. Neither are these responses mere passive mouldings ; the powers of individual ad- justment, no less than the general adaptive characters of the species have been attained by the putting forth of variations, the steps by which species travel. Heredity, the name we have given to the mysterious power of plants and animals to follow accurately the developmental pathway of the species, and even to repeat the individual pecu- liarities of the parents, is more similar to memory than to any other biological phenomenon. Professor Lankester's concep- tion of the facts implies that the hereditary memory is imposed from without, that it is stamped or moulded upon the species by the environment, and that its strength is, or should be, propor- tional to the time during which the environmental impression is continued. It is true that new or recent environmental reac- tions, or direct adaptations, are not inherited, and do not replace the older responsive characters of the species, but this fact lends no support to the doctrine of environmentally moulded heredity, for other character-modifications do appear suddenly, and do immediately and definitely replace the earlier type of the species, as shown in numerous and well established instances of genetic variation and mutation. These modifications of ASPECTS OF KINETIC EVOLUTION 335 heredity have no doubt adequate physiological causes resident in the species, but as far as the environment is concerned they seem to be thoroughly spontaneous and fortuitous. They ap- pear without notice and bring their own new and complete heredity with them ; their very appearance signifies and consists in an abrupt modification of heredity. The environment may reject the new character and extinguish all the individuals with the modified system of heredity ; it may limit heredity through selection, but it does not mould or modify heredity. Heredity has been defined, in accordance with Professor Lankester's view, as the sum of past environments, but this statement, as usually understood, is only partial and misleading. It is true only to the extent that it means that the heredity of a species is a summary of the variations which the environments have permitted it to retain. The idea, for example, that im- proved environments will change the inherent characters of backward races of mankind or of the deficient and criminal classes of our populations, as often stated by philanthropists, is founded on teleological inferences, and not on concrete observa- tions. New environments may permit new and desirable char- acters to be put forth which the selection of adverse conditions has forbidden hitherto, but humanitarians seldom have patience with such time-consuming methods of improvement. Moreover, if they were to view the subject from a biological standpoint they would soon appreciate the desirability of selecting the good stocks for further amelioration instead of wasting their efforts, relatively, at least, upon unworthy materials, in the vain hope of realizing an unnatural ideal of equality. Ethical considera- tions which concern only the relations of individuals and or- ganized social bodies are often applied to racial and other questions as purely biological as those of the relations of species and subspecies in any other department of nature. Our chief duty with reference to the really backward and deficient races is to keep them from bringing about the deterioration of our own, as almost inevitably occurs when a higher race comes in contact with a lower. The qualities and standards which con- duce to fitness in a higher civilization are of little or no signi- ficance in a lower, and rapidly deteriorate. This does not 336 COOK prove that the higher qualities are caused by the environment, but only that they require certain conditions in which to develop and maintain themselves. Environment is of the first importance to individual organ- isms, but the inference so widely drawn in scientific and general literature, that the environment causes and controls evolution, is essentially fallacious. It controls, in a measure, by limiting some of the avenues of advance, or by setting higher and higher requirements for continued progress, but life finds mil- lions of different ways to solve its environmental problems. Given a particular environment and a particular selection of individuals with their hereditary qualities and habits known, and we may with confidence expect a fairly definite reaction in line with previous experiments of the same kind. But this does not mean that evolution is an environmental cul de sac. Changes are not passive merely, but kinetic. The environmental possi- bilities are persistently tested by many variations. Species have retained in this way the power of ameboid motion, and have thus crept over the whole face of nature, and into all the crevices. The progress possible in a single life-time or generation may be small, but the lesson is plain. The largest, most practical, and most precious factors of amelioration for plants, animals and men, lie in the discovery and preservation of those indi- viduals which are in the line of evolutionary advancement for the breed — those possessing the qualities required by the en- vironment, and which at the same time strengthen the species and help to maintain the necessary vital motion in courses of beneficial change. THE PURITY OF GERM-CELLS AND CHROMOSOMES. In the search for causes of natural phenomena an important step appears to have been taken when definite quantitative re- lations have been established. It is not strange, therefore, that the discovery of Mendelian or "disjunctive" hybrids should have aroused much interest, and even a certain amount of excite- ment, among biologists. Mathematical considerations have been allowed to obscure biological facts, and Mendel's "prin- ciples of inheritance" have been declared to be as fundamental ASPECTS OF KINETIC EVOLUTION 337 and significant for biology as Dalton's law of definite propor- tions for chemistry. Deductions from Mendelism followed in rapid succession, such as the purity of germ-cells, inheritance by character-units, and the localization of these in chromosomes. Mendelism as a phenomonon is both interesting and sugges- tive, but it lacks warrant as a generalization, because the con- ditions imposed by the experiments are as likely to be the cause of the results as the general principles of heredity alleged to have been revealed. There are, in fact, many reasons for believing that the inbreeding which is deemed an essential pre- liminary to experiments in Mendelism, induces the "disjunc- tion " of the hybrids, instead of the purity of the germ-cells or the antagonism of " dominant " and " recessive " character- units. It is, perhaps, to be expected that Mendelism can be found whenever the conditions of the experiment can be met, but this does not prove that the phenomenon is a normal one. Still less has it been shown that Mendelism has been a con- tributing factor in evolution, since in Mendelian hybrids the more recently derived characters are held not to be dominant, but recessive, and would thus have the less chance of being preserved under natural conditions of unrestricted crossing. Some writers have claimed for Mendelism a practical utility as determining the methods of procedure in breeding, and many plants and animals are being bred to learn which characters are dominant and which recessive, it being taken for granted that such facts have a fixed and definite value for each species or variety, thus enabling the results of breeding combinations to be known in advance. The utility of such knowledge is, nevertheless, negative rather than positive ; it may keep the breeder from attempting the impossible, but it seldom gives him new leverage in attacking practical problems. The danger is rather that the acceptance of erroneous theories of heredity may delay his perception of facts and discourage his efforts. It seems to be agreed by several experimental evolution- ists that white fur or feathers is a recessive character ; but no attempt has been made to test the general basis of this assumption by comparing interbred white mice with inbred gray mice. Albinism is one of many mutations induced by 338 cook inbreeding, and this debilitating process has been continued with white mice ever since the original specimens were caged, while gray mice have mostly remained at liberty until needed for breeding experiments. To overlook these historical differ- ences is to neglect factors of known significance for those of purely hypothetical meaning. A second series of pertinent facts commonly ignored is the frequent and perhaps general dominance or prepotency of muta- tions when bred upon their own immediate blood-relations. Commercial white mice are a long standing breed, with no close and equally inbred gray relatives. To test prepotency fairly a new mutation would be required. There are numerous instances in literature, but experimenters naturally attach special importance to what happens in their own cages. For a third experiment which might afford conclusive evi- dence on the pure germ-cell theory, some of the more recently developed varieties of mice might serve. If two varieties of independent origin which had been crossed separately with mice of the ancestral type and found to mendelize, were then crossed with each other and found to revert to the parental type, experi- mentalists might admit that the doctrine of pure germ-cells had been definitely disproven. The mice which in the Mendel experiments had produced pure white, yellow or black germ- cells would later have produced gray germ-cells. And yet this possibility in crosses of selected domesticated varieties has been known since the time of Darwin's experiments with pigeons. The arrangement of the chromatin granules into chromo- somes, to which so much importance is ascribed, is a very tempo- rary phenomenon. The chromosomes do not appear to retain their separate identity either during sexual fusion (mitapsis) or during vegetative growth, when the activities of the cells are bringing to expression the qualities which have been transmitted through the gametes. The diversity in number of chromo- somes in closely allied species, or even in the same species, also tends to weaken our faith in the idea that chromosomes as such, or as character groups, play a very definite or determining part as governors of the form of the organic structure of the indi- vidual plant or animal. The chromosomes may prove, after ASPECTS OF KINETIC EVOLUTION 339 all, to be merely crowds of chromatin granules which are being assembled from the vegetative nucleus for mitapsis, and redis- tributed after mitapsis to resume the functions of control over vegetative growth. Adult organisms, with their various characters, do develop out of germ-cells, but until we know something more of the nature of protoplasm, there can be no certainty that the individual char- acters of the adult are in the germ-cell in any such form that we can look in and find them. As well might we undertake to find in human embryos or infants the mental and moral char- acters of adult persons. All that we can be sure of is that the potentialities are there, but the nature, form and residence of these potentialities can be discussed only by means of abstract inferences, and are not yet accessible to the concrete imagina- tion. This explains why the theories of hereditary mechanisms are merely philosophical or mathematical, not biological. Even if the conception were correct and it were possible to ascertain by some extension of microscopic vision that chromosomes or granules are prefigurations of adult organisms, the fact would still have little use as an explanation of heredity, or even as a working hypothesis, until we could learn, or at least imagine, how the models could build the structures. It is as though some barbarous tribe, on being visited for the first time by a modern man-of-war, should think to explain the structure by finding a small model of the ship in a glass case in the saloon. There would simply be two ships to explain, instead of one. Indeed, the discovery of the character-unit mechanism has been so long and so vividly anticipated that it is not altogether unjust to mention the fact that no very definite uses for such a con- trivance have been suggested. The studies of Boveri tend to show that in one group, at least, there is a definite necessity for the presence of one full series of chromosomes to make normal development possible, but this is still very far from showing that individual chromo- somes or granules correspond to different parts of the animal. A mutilation or disarrangement of the organs of the germ-cells might well interfere with their development into normal indi- viduals, even if the adult organism were not prefigured, pre- 340 COOK formed, or prefixed, inside the reproductive cell. It is highly important, of course, that the nature and extent of all determi- native relations be known, but until the nexus, the modus operandi of the process has been learned, predetermination by material particles has no special standing as a theory, especially where the resulting concept of heredity fails to accord with concrete, facts, such as the need of normal heterism and free interbreeding. To those who view the matter from the mathematical side only, it is still impossible to -prove that essential changes occur in mitapsis which make the chromomeres and chromosome aggregates different from what they were before the fusion took "place. Nevertheless, there are three facts of nature, universal and much accentuated among all the higher plants and animals, which these theories of construction of organisms by character-unit mechanisms leave entirely out of account, with- out physiological meaning or explanation, (i) the diversity of the individual members of species, (2) the elaborate adaptations for interbreeding, and (3) the conjugation of the granules in mitapsis. The different assortments of chromosomes or gran- ules might explain the diversity, but they show no use or reason in it. They may cause, too, the adaptive characters of inter- breeding, but still for no purpose. Finally, they perform the elaborate evolutions of mitapsis, but all without result, accord- ing to these hypotheses of purity of germ-cells or of chromosomes. For numerical purposes it may be that all these complexities of symbasis are useless and unnecessary. The diversity of genera and species, and of the individuals inside the species, could all be worked out arithmetically if we could be provided beforehand with the determinant mechanisms and a system of permutations for combining them. But from the biological standpoint it seems equally clear that this is not the way the organisms were developed in nature. The character-unit plan might have avoided all these unexplained and apparently un- necessary complications of heterism and symbasis. The diffi- culty is that, like its progenitor, the static theory of evolution by environmental causes, it seems not to be followed in the organic creation. Organisms are not naturally uniform and ASPECTS OF KINETIC EVOLUTION 341 they do not tend to stay uniform. Organisms are not naturally pure-bred, and their tendencies are ever to be mixed more and more. This is the overwhelming testimony of the facts of nature, which the inventors of character-unit mechanisms would do well to canvass before entering upon their labors. Chromosomes and granules as parts of cells are morpho- logical entities, in the sense that they exist and can be made visible by microscopical technique. It does not follow, how- ever, that they are biological or evolutionary entities, or that they can properly be thought of as having any general evolu- tionary significance, except as parts or organs of cells or of or- ganisms, which are the units of life. Moreover, as already in- dicated from other considerations, not even organisms can be considered units of evolution, which requires the coherent net- work of descent of a normally diverse, interbreeding species. CONTACTS BETWEEN LINES OF DESCENT. The fact that the lines of descent are joined only in repro- ductive cells should not be taken to mean that there is merely a single or casual contact between them, nor prevent our recognizing the possibility that the functions of the chromatin granules may be physiological rather than morphological. It is through them, evidently, that the reorganization of the proto- plasm of the cells is accomplished. They represent the citadels of life, the most vital points of the cell substance. The final stage and apparent purpose of the process of conjugation is to bring them into contact with other granules from other lines of descent. The nature of this contact, whether the granules exchange particles, or renew their vital energy by molecular or other adjustments, is still unknown. The most recent results of cytological investigation are in accord with the supposition that the ability of the higher plants and animals to lessen the number of conjugations and prolong the intervals of vegetative growth, has been attained by the development of more and more efficient methods of conjuga- tion. A few years ago the opinion was held that the proc- ess of synapsis involved only a fusion and reduction of the number of the chromosomes ; it now appears that the 342 COOK chromosomes are not the ultimate units of the nuclear structure, but are merely aggregates of granules of chromatin. In the final stage of conjugation (mitapsis) the chromosome aggregates no longer appear distinct, but are subdivided into small clusters of granules called chromomeres. The chromomeres are strung out like beads in single file along two slender, protoplasmic threads which finally lie parallel and close together, so that the individual chromomeres can be paired off and fused with each other. Instead, therefore, of thinking of conjugation as a simple bulk fusion of protoplasm or of nuclei, we must view it as involving a long line of many scores, hundreds, or even thousands, of contacts or combinations between the much smaller granule-groups or chromomeres. Chromomeres appear, there- fore, to have important physiological functions as specialized contact points in the fusion and reorganization of the protoplasm, and do not need to be thought of as bearers of hereditary char- acter-units. There remains one other stage of elaboration of mathematical hypotheses of heredity, to treat the chromomeres as permanent entities of descent and deduce the infinitely multifarious diver- sities of individuals in nature from the infinity of combinations and rearrangements of which the chromomeres may be capable. This theory is complete and unimpeachable mathematically, but is as indefensible biologically as its predecessors ; for like them it rests on the assumption that the bringing of the chro- matin granules into contact in mitapsis has no significance in descent. It takes for granted that nothing of importance oc- curs when the granules appear to fuse, and that they separate again without mixture, interpenetration, or combination, of the granular or fluid constituents of the protoplasm. The character-unit assumption requires us to imagine some way in which the particular granules could create or bring about the existence or the accentuation of the particular character, whereas the other interpretation, by lines of descent, does not needlessly destroy the unity of the problem of heredity. It avoids the necessity of elaborate and gratuitous hypotheses in a field which science is scarcely prepared to enter. As in the adjoining regions of instinct and memory, it is easy to ascribe the phe- ASPECTS OF KINETIC EVOLUTION 343 nomena to positional or other relations of molecules or atoms of the cerebral tissues, but impossible to imagine an adequate nexus of association with the concrete facts, actions or functions. The opinion has already been recorded in another place that truly mechanical solutions of this series of problems are likely to await the recognition of additional properties of matter, which physical researches are now revealing with such startling rapidity.1 As clearly perceived and definitely stated by Lord Kelvin, the current conceptions of physics are not adequate for the treatment of the problems of biological evolution. The wonderful and altogether unexpected results of studies of the internal structures of cells are but poorly appreciated by those whose hopes have dwelt on the discovery of mechanisms of heredity. From the morphological standpoint it may appear that little has been obtained except to open another chapter in the vast complexity of nature. The internal organs and proc- esses of cells have their multifarious similarities and diversities, like all other phases of organic existence. Reproduction is carried on by as many different methods as assimilation, res- piration or locomotion. The great and surprising result of cytological investigation is not in learning that such diversity exists, which might have been anticipated, but in ascertaining that the evolution of the large and complex bodies of the higher plants and animals has been made possible by the evolution of superior methods of reproduction. Mechanical theorists have been so intent on finding a mechanism of heredity that they have failed to recognize the physiological significance of an improved process of conjugation. The older idea was that reproduction, that is, the production of a new individual plant or animal, followed the conjugation or complete union of the parental germ-cells, but it has been found that this is not true of any of the higher types of life. What has been considered conjugation among the higher groups, that is, the process in which the characters of the new organism are determined — as far as they are determined in the germs — is not a complete conjugation of the germ-cells, but only the begin- ning of a conjugation which continues throughout the life of the new individual. ^ook, O. F., 1904. Evolution and Physics. Science, N. S., 20: S7. 344 cook This fact has bearing upon the conception of heredity, for it takes us another step away from the older idea of a mechanism in the cell, and shows us that the intracellular organs, which some look upon as the mechanisms of heredity, are capable of change and adaptation like other parts of organisms, and that the problem of evolution is not to be solved by the supposition that evolution is determined in advance by mechanisms of heredity. In the lower groups the union of the gametes is completed before vegetative growth is resumed, or before the new genera- tion begins. But in the remote ancestors of the higher groups this procedure was abandoned, and the completion of conjuga- tion was deferred. Vegetative growth began to be carried on while the cells were still in the double, conjugating condition. If the form of the adult were strictly predetermined by the inter- nal organs of the cell, the double-celled organisms could have existed only as monstrous doubles of the simple-celled organ- isms which are built up after conjugation is completed. But, as a matter of fact, the structures which were built up from these double, conjugating cells proved to be entirely different from those which had been built previously from simple cells. New evolutions began on entirely independent lines, without refer- ence to the character-units or other equipment of heredity resident in the cells of which the new structures were built. Moreover, the old form of heredity continued to be transmitted, even after new and higher types of organic structures had been intercalated into the life-history of the primitive organism. All the liverworts, mosses and ferns continue to build up the two different kinds of cellular structures, one during conjuga- tion and the other after or between conjugations. The two kinds of heredity, the conjugate and the post-conjugate, continue to run peaceably along the same lines of descent, like multiple telegraphic messages on the same wire. Such complications do not, of course, dismay the inventors of hereditary mechanisms. Difficulty only adds zest to their ingenuity. Having invented one set of determinants, it is easy to invent another and have them working by turns, as Weis- mann gravely proposed in explaining the alternative heredity of ASPECTS OF KINETIC EVOLUTION 345 sexes. For the bees and ants three kinds of mechanisms were provided, and for the termites four kinds, though in reality up- wards of a dozen sorts would be needed to account for the strange diversity of types found in some of the African species. And the most curious thing about the ants and termites is that the animals which exhibit the supposed results of these diverse kinds of mechanisms do not transmit them at all, but are de- scended independently in each generation from sexual insects. Here again it is apparent that new methods of development have been entered upon without requiring any change or dis- placement of the old. With the bees, at least, the heredity is not determined when the egg is laid, or even when it hatches. It is still possible for two or three days to induce the young larva to develop either into a queen or into a worker, by vary- ing the nature and amount of food. The environment deter- mines, evidently, which of the mechanisms shall continue in play and which retire into desuetude. There is no need, of course, to continue the discussion in this direction ; doubtless it is too long already. There are those who think only in relations of numbers and spaces ; and for these mechanical forms are a necessity. But for those who approach from the biological side, who are curious to understand nature, and yet not so impatient as to accept even scientific fic- tion at the expense of ascertainable fact, these character-unit mechanisms of heredity do not appear to help, but rather to hinder, clear perception and exposition. ALTERNATIVE OR POLARIZED HEREDITY. From the standpoint of the kinetic theory it appears possible to reconcile the proposed character-unit phenomena of Men- delism with other facts of alternative descent, without invoking the hypothesis of character-units and pure germ-cells. The phenomena of heterism and symbasis, that is, normal diversity and broad-breeding in specific groups, do not necessitate the character-block assumption. They only require us to suppose that diversity of descent affords a certain amount of molecular tension or attraction, a polarity, as it were, between proto- plasmic elements derived from the different lines of descent. 346 cook There also appears to be a complete series of stages of accentua- tion of this polarity of descent. The most primitive condition is that of indiscriminate or unspecialized heterism, in which a character shows all degrees of expression from the lowest minimum to the highest maximum, with a preponderance at some intermediate or optimum point. The physiological advantages of diversity of descent not only prevent the species from concentrating or stagnating on a cen- tral average or optimum point, but they often favor the develop- ment of two optima. The connecting series of character-stages may weaken, or it may entirely disappear, except for rare abnormalities, the normal form of the species being represented by the two separated extremes. The typical and most familiar instances of specialized heterism is to be found, of course, in the phenomena of sex. The primary sexual characters are now so intricately involved with the functions of reproduction that their significance as specializations of heterism is much obscured, but large numbers of secondary sexual characters are quite functionless for any purpose thus far detected, except this of increasing the diversity of descent inside the species. When once a species has reached the stage of sex-differen- tiation, and has thus established a polarity of descent, the ten- dency seems to be for other specializations of heterism to group themselves with sex. The result is to give each generation the benefit of full diversity of descent, instead of losing this advantage in cases where similar individuals might breed together. No doubt it is easier, too, for a new character to join with and accentuate an already established polarity than to establish a new one for itself. Even among the plants which have not attained differentiation into separate sexes there are definitely alternative characters, and sometimes there are not merely two alternatives, or two groups, but several, and in a variety of combinations, as in the genus Lythrum. In insects the phenomena of alternative descent reach their highest ac- centuation and complexity, for there they are superposed upon the sex-differentiation. There may be two distinct forms of one of the sexes, as among the bees. In some species of termites both sexes are capable of specialization in several dif- ASPECTS OF KINETIC EVOLUTION 347 ferent directions, so that more than a dozen different and dis- tinct types of individuals may be found in the same colony, and no intermediate forms. The equal sharing of the two sexes in these wonderful specializations of the termites is a reminder of the general fact of numerical equality between the sexes. Among the bees where the male sex is completely useless in the social economy and environmental relations of the colony, the reduction of the number of males has been accomplished only by the very re- markable specialization of the reproductive process. The sex is no longer determined by a polarity or other simple relation which would give equality of sexes, but by the queen herself, who has the power of laying at will either fertilized or unferti- lized eggs, the former developing into females, the latter into males. This arrangement appears peculiar because it consti- tutes so radical an exception to the general rule of equality in the choice by individuals of one or the other of the two routes of development possible in all sexually differentiated species. If these relations depended upon merely mechanical arrange- ments or upon the relative numbers of different kinds of pure germ-cells, we should expect the frequent occurrence of many definite deviations from equality of sexes. Experiments have shown that in some groups of animals and even in plants the sex-determination may be influenced by the conditions of existence, and particularly by nutrition and tem- perature. The changes are supposed, however, to occur in continuous series of gradations, as though brought about by general influences upon the constitution of the organism, rather than by the abrupt changes of adjustment which might be ex- pected to result from the action of character-unit devices. The phenomena of Mendelism constitute an extension of the facts of alternative descent ; for they show that this is not limited merely to secondary sexual characters and to the form differ- ences of polymorphic species, but that closely similar effects can be obtained in a somewhat artificial manner, by com- bining domesticated varieties with properly opposed characters. Instead of producing merely averages or miscellaneous grada- tions of intermediates, well established and contrasted differ- 348 cook ences are preserved separately, like alternative sexual differ- ences. Instead, therefore, of considering that Mendel's Laws explain sexuality, it seems more reasonable to assimilate the Mendelian phenomena with those of normal alternative descent as shown generally in sex-inheritance. If the principle of alternative or polar heredity applies to Mendelism, the earlier explanations by the special character- units, segregated in different germ-cells, will be superfluous. The phenomena would still be abnormal, as are the conditions under which they appear, but they would no longer need to be associated with the phenomena of incompatability of chromatin, described by Guyer in sterile hybrids between diverse species. " When germ-cells are to be matured, before the real reduc- tion, there is in most forms a so-called false reduction, in which the chromosomes fuse in pairs so that there appears to be only half the normal number present, though in reality each is double (bivalent) and equivalent to two of the simple (univalent) type. The doubling of chromosomes which normally occurs at such times is frequently incomplete, or lacking, in hybrids. This is especially true if the hybrids are from widely separated species. Instead of a normal spindle bearing the usual number of bivalent chromosomes, multipolar spindles, or two separate spindles may appear, thus apparently permitting the two kinds of parental chromatin to remain apart. In the most extreme cases a complete separation may occur subsequently, the entire chromatin of one parent occupying one cell, that of the other a different cell. Such visible separations, however, only occur extensively in sterile hybrids from markedly different parent species. Fertile hybrids from closely related forms, for the most part, display spindles normal in appearance. . . . " In the case of these milder fertile crosses, then, where rever- sions follow the Mendelian law, the germinal incompatibilities must be narrowed down to the qualities themselves rather than confined to the respective germ-plasms as a whole. These qualities must separate and each take up its abode in a different germ-cell irrespective of whether the other qualities of that par- ticular germ-cell are of a different parentage or not. The cases in which the entire plasmas are segregated are then prob- ASPECTS OF KINETIC EVOLUTION 349 ably but magnified images of what occurs among the specific qualities of the milder crosses. The interesting possibility arises that if fertile hybrids can be secured from widely different species the plasmas of which must be more incompatible than those of nearly related forms, such hybrids will give rise to offspring in which there is reversion, not only of one character, but of many or all characters in the same individual, due to a more thorough segregation of the parental germ-plasm as a whole. In other words, the farther apart the parent species are, the more complete will be the return in any given offspring which shows reversion." l Instead of representing germinal incompatibility, the Men- delian phenomena may prove to be merely examples of the preservation of welcome and desirable contrasts. Nor is it unreasonable to suppose that the polarity or other form of alter- native reaction is rendered more definite and intense by the process of inbreeding which is considered a necessary prelimin- ary for the exhibition of the Mendelian phenomena. Con- trary to Dr. Guyer's supposition, the " disjunction " of characters does not appear to depend upon the extent of diversity, but upon conditions of inbreeding. Experiments with Mendelism seem to succeed only with closely inbred domesticated varieties, not with wild species. Indeed, it is only among narrow-bred do- mesticated varieties that materials for such experiments can be found, that is, definitely contrasted pairs or small groups of uniform characters. SEXUALITY OF CONJUGATE ORGANISMS. The sexual differentiation of the higher plants and animals affords another fairly definite indication that sexual and other alternative characters are determined by some such general principle as polarity, rather than by specialized character-unit mechanisms of the reproductive cells. It is now known that the bodies of higher plants and animals are not the result of a com- pleted conjugation of the parental sex-cells, but are formed be- 1 Guyer, M. F., 1903. The Germ Cells and the Results of Mendel. Cincinnati Lancet-Clinic, May 9. 350 COOK fore the conjugation is completed, and are thus a joint or conju- gate product of the two germ-cells. The sexuality of the higher plants, known to the ancients, and to the aborigines of tropical America, reasserted by Bacon, re- discovered by Sprengel and substantiated by Muller and Darwin, has been denied on technical grounds by recent botanical writers, as a result of the prevalence of certain morphological theories of alternation of generations. This doctrine has led to the inference that the bodies of our higher flowering plants represent an "asexual generation," and it is held to be absurd to ascribe to such organisms the qualities and specializations of sexuality. Some botanists accordingly refuse to call the stamens and pistils sexual structures, or the staminate and pistillate plants male and female, because they do not represent the same kind or stage of sexual differentiation as that shown in male and female moss-plants or male and female fern-prothallia. The fact remains, however, that the sexuality of such a plant as the date palm is completely analogous to the sexuality of the higher animals and of man himself. In other words, it has been proposed to deny sexuality to exactly that form of sex- differentiation to which the word was originally applied. The significant fact is that the sexual differentiation of organisms should have taken place on the two different planes of structural organization, both in the simple-celled lower types and in the conjugate-celled higher types. Indeed, there are three grades or stages of development where sexual diversifica- tion has taken place. i. Sexual differences of the single gametic cells, as of the sperms and ova, or the pollen-grains and the egg-cells. 2. Sexual differences of simple-celled gamete-bearing struc- tures, as of the male and female thalli of liverworts, the male and female plants of mosses, and the male and female pro- thallia of ferns, Isoetes, Selaginella and Equisetum. 3. Sexual differences of double-celled or conjugate struc- tures, as of the male and female individuals of the higher plants and animals. Nor does the reckoning end here, for the separation and ASPECTS OF KINETIC EVOLUTION 35 I diversification of the sexes has not taken place twice only among the plants, but probably hundreds of times, independ- ently, and in different and unrelated natural groups, the ances- tors of which were bisexual. Separate sexes, though well-nigh universal among the higher animals, both arthropods and verte- brates, show, nevertheless, numberless independent specializa- tions. In short, no tendency of evolution has been so definite and so general as that leading toward the accentuation of sexual differences. This can hardly mean anything less than that diversity of descent, to which sexuality ministers, has a general physiological importance and is not merely incidental to fortuitous collocations of character-units. No doubt it will be found that the details of sex-determination differ much in the different groups of animals and plants, but this will not diminish the general significance of the phenomenon. Sex-determination by purely mechanical means might still serve the purposes of symbasic interbreeding, but the heredity which might be due to the existence and operations of such mechanisms would not afford the basis of a complete theory of evolution. It would still be in need of an evolutionary explanation. VEGETATIVE MODIFICATIONS OF HEREDITY. Further reasons for preferring this idea of polar or positional relations of the ancestral hereditary elements to that of charac- ter units or determinants, is to be found in the fact that the hereditary attributes of form and structure are apparently ca- pable of change at any time in the life-history of the organism, and not merely at the time of conjugation when under the more mechanical theory the nature of the individual should be deter- mined, once for all. As a matter of fact, plants do make extensive and permanent alterations of their characters during the vegetative period. Such cases, though relatively rare, are numerous in the aggre- gate. The best known instances are those of bud varia- tions or "sports/' as the gardeners call them, where^a single bud produces a branch as different from the others as seed- grown individuals, or more so. A bud mutation of coffee found 352 COOK in Guatemala in 1904 showed characters often approached by- seedling mutations, but somewhat more accentuated than any of the similar mutations which have been raised from seedlings. Fasciation is, perhaps, to be looked upon as a form of bud variation, but it must rise in some instances, at least, through a derangement of the apical cells, rather than as a mutating adven- titious bud. This has been observed very frequently in fascia- tions of asexually propagated plants like Dioscorea and Ipomcea. A normally round stem broadens gradually to several times its normal width, but retains its original thickness or even becomes thinner than before. Another instance in which heredity, in the usual sense of the word, is suspended or set aside during vegetative growth, may be found in the familiar phenomenon of galls, where the presence of the insect parasite or the substances secreted by it, is able to cause the formation of complicated and highly specialized structures, as though new ingredients of heredity had been added. The mutations which often occur in the first generation of plants when grown in new regions are also to be reckoned as post-reproductive changes of the hereditary type, for while we could not be certain in any individual case, that the mutation could not have occurred if the seed had not been transferred, the very great difference in the percentage and the range of mutations which can be secured from the same stock of seed will prove that the new conditions have been an inducing cause, able to act after the planting of the seed and long after the nuclear elements have been arranged on a basis which would normally have persisted throughout the life of the individual. The fourth type of interference with heredity during the vegetative period is that of graft hybridism. The extent to which this takes place with normal plants has not been ascer- tained, but the power of communicating diseased conditions has been well established in a variety of instances ranging from peach -yellows, peach-rosette, and the mosaic disease of tobacco, to the only slightly abnormal variegations. Mr. Luther Bur- bank relates also an instance in which a graft of a red-foliaged variety of Primus influenced the foliage and the progeny of the stock. ASPECTS OF KINETIC EVOLUTION 3 53 RELATION OF HEREDITY TO IIETERISM. The recognition of normal diversity inside the species neces- sitates a modification of the older view of heredity which predi- cated an exact likeness among the members of a species. The uniformity which the older authors had chiefly in mind was that of the members of one species compared with those of another species. This is indeed a wonderful phenomenon, and it is not surprising that mechanical explanations were suggested. It was also quite to be expected that when the idea of internal "mechanisms of heredity" had arisen it should have seemed necessary to predicate a complete uniformity of individuals as the normal result of the workings of such a device. The mechanical inference was carried even to the extent of suggesting that the diagnostic characters like those enumerated in system- atic manuals are each represented by one of the chromosomes or minute masses of infinitesimal granules found in the nuclei of reproductive cells. As a matter of fact, natural species do not differ merely by six or seven formally expressed characters. They are different throughout, and the diversity does not end with the distinctions between the species, but extends to the individuals of each of the groups. Appreciating the necessity of greater flexibility for the mechanisms of descent, Mr. Walter T. Swingle suggested several years ago that the expression of characters might not depend directly or entirely upon the chromosomes or granules themselves, but upon their positional relations. This sugges- tion avoids all occasion of resorting to the character-unit hypoth- esis, and may afford a clue to a cytological explanation of the phenomena of heterism.1 It is not necessary to think that the granules determine the characters as such ; they need be considered only as representing the characteristics of the ancestral lines of descent. It is then 1 Mr. Swingle also calls my attention to the very pertinent fact that the nar- rowly mechanical character-unit hypotheses, to which objection is taken in the present paper, have not been proposed or defended by those who have made the truly important contributions to the science of cytology. Indeed, it is exactly these investigators with first-hand knowledge of the anatomy of cells who appre- ciate most keenly the wholly hypothetical nature of the character-unit specula- tions. 354 COOK possible to suppose that if the granules derived from a given ancestor secure a favorable position the characters of that ances- tor will predominate in the new individual. In this way the characters of different ancestors might assert themselves in end- lessly varied degrees, even in the offspring of the same parents, as they often do. This theory has the advantage of affording a thinkable connection between facts which otherwise appear completely mysterious. Two collateral circumstances increase the warrant for applying the suggestion to the phenomena of heterism. It has been indicated by several observers, but most directly by Prowazek l that the granules of chromatin, which compose the chromosomes at the period of the conjugation, migrate, dur- ing vegetative growth, to positions at the knots of the nuclear network, as though to direct the processes of assimilation and growth. It was found by Maupas in his experiments with infusoria that continual inbreeding causes the gradual deterior- ation and diminution of the nucleus, as though diversity of descent were necessary to maintain the nuclear network, either by keeping up the number of granules or by enabling them to stay at the right distance apart. Such a relation would explain the known facts, to the extent of indicating a reason for heterism and a means for bringing it about.2 It is also easier to conceive of the possibility of bud-variations under the supposition that the influences exerted by the chrom- atin depend upon position, rather than upon the origination of new units or upon the making of different combinations. Modi- fications of hereditary forms and methods of growth do occur during the vegetative period, as already stated, and may be quite as pronounced as the mutations obtained from seed. Changes capable of accounting for bud-variations would also be adequate for the explanation of mutative variations. Those who begin with the assumption that evolutionary prog- ress is actuated by external causes are compelled to argue that the diversities of individual organisms arise through varied 1 Prowazek, J., 1904. Keimveranderungen in Myxomycetenplasmodium. Oes- terreich. Bot. Zeitsch., 54: 27S. 2 Cook, O. F. and Swingle, W. T., 1905. Evolution of Cellular Structures. Bui. 8i, Bureau of Plant Industry, U. S. Dept. of Agriculture. ASPECTS OF KINETIC EVOLUTION 355 environmental experiences, but the inadequacy of this con- jecture is made plain by the fact that the greatest of these intra- specific divergencies, those of sexes, castes and alternating generations are obviously not subject to such an explanation. Protoplasmic arrangement, and the specializations of the organs and processes of reproductive cells, were not, of themselves, effective for the problems of advancing organization. There had to be differences, vital tensions, as it were, between the protoplasms, if organic progress were to be maintained, and con- jugation were to become adequate for the building up of large, complex and long-lived organisms. As fission suffices for the reproduction of only the simplest types, and haplogamy, apaulogamy and finally paragamy, have proved necessary to continue the propagation of organisms of successively higher degrees of complexity, so, for the very highest, sexual diversity and continuously maintained symbasis are requisite. The effect of prolonging the process of con- jugation is to double in each organism the threads of the vital network. The separation of a species into sexes is a still more advanced category of specialized descent, since it doubles the whole specific network, permits accumulation of two sets of variations, and insures that each individual be descended from two diverse parents. But even this provision of interbreeding does not suffice to maintain the perfection of organic excellence found in man himself, where the requirement of diverse descent is so acute as to forbid, on pain of degenerate offspring, the union of indi- viduals separated by less than four or five generations, or by two or three strains of alien blood. Human descent is so difficult and precarious a fabric that the double network cannot be held in place merely by the joining of adjacent knots. The structure is likely to totter or fall if the lines of descent which join in the building of each new individual are not well braced by meeting each other at broad angles. Neighboring parallel or only slightly divergent lines do not afford the neces- sary stability of contrast, the vital tension which enables the con- jugate cells to build a well-knit body. The intricacies of rela- tionships which fascinate the genealogist are not gratuitous or 356 cook accidental, but are a biological necessity in the elaboration of the framework of symbasic descent which sustains the organic vigor of the species. In cytology, no less than in the more general fields of study, it is the physiological values which need first to be ascertained? before the morphological considerations can be correctly appre- ciated. Germ-cells can indeed be viewed as mechanisms of descent, but speculations regarding them should not be made the basis of evolutionary thought nor the test of orthodoxy, to the exclusion of more definite and concrete indications of the nature of evolutionary processes. The kinetic theory finds significance and confirmation in the now rapidly accumulating indications of an extensive series of fusions between the individual granules of chromatin, which previous cytological interpretations, based on static views of evolution, have denied. From the kinetic point of view the fusions of the chromatin are an important and altogether ac- cordant part of the whole system of evolution ; they are the ac- tual knots and junctions of the fabric of descent. Static theories of cellular determinants, on the other hand, can see in these evidences of fusion only an elaborate deception, an unnecessary complexity of the process of reproduction, just as it was for- merly held that sexual reproduction itself stood in the way of evolution, because it interfered with the subdivision of species and the isolation of new variations. The traditional concept of heredity, the ideal of uniformity in descent, has furnished the basis of all preceding doctrines of evolution. Conditions of isolation or of restricted descent have accordingly been considered typical for evolution, because it was only in narrow bred groups that the ideal of uniformity could be approximated in nature. The kinetic theory breaks with all these traditions, and seeks to substitute for the abstract concep- tion of a uniform, definite or mechanical heredity, a recognition of the concrete fact of normal diversity, inside the species. 6. THE CONSTITUTION OF SPECIES. Astronomy is reckoned as queen among the sciences because it has demonstrated that definite and orderly relations exist ASPECTS OF KINETIC EVOLUTION 357 amidst the apparently hopeless disorder of the stars. The ancients, grouped the stars into constellations, but modern science shows us systems ruled by laws of mathematical preci- sion. Biology has remained longer in the constellation stage. Spe- cies are still discussed, even by evolutionists, as though they were mere chance aggregates of organisms, at once too familiar and too diverse to be formally defined. It may well be that no coherent definition can be made for species as mere aggregations or constellations of organisms ; the idea itself is vague and essentially unscientific. The pri- mary error was that of treating the species as a morphological group, whereas the true evolutionary species is a physiological system. Like a stellar system, it may contain a large number of different individual members, and even different kinds of members. The unity of the species does not depend upon the organisms being all alike. It is necessary only that they remain within range of mutual influence through interbreeding, which is the biological analogue of gravitation. A species, that is, a normal, natural, evolutionary species, is a large, coherent group of freely interbreeding organisms. But with species, as with stars, all systems are not alike. There are suns, satellites, planets, asteroids, nebulae, variable stars, doubles and comets, in vast diversity of sizes and combina- tions. In biology, as in astronomy, the most familiar things have proved very deceptive. The sun, moon and stars appear alike to revolve around the earth, from east to west. It was at first an extremely heterodox idea that the earth revolves around the sun. Moreover, neither of the apparent motions gave any inti- mation of the third order of motion, that of the system as a whole. In a similar way we have taken it for granted that the evolution of species could be explained by the motions we have been able to detect among our domesticated plants and animals. We are now learning that these types of life are not reliable examples of evolutionary systems, that their motions are often retrograde or degenerative instead of progressive and construc- tive. Nor are abnormal evolutionary conditions entirely con- 358 cook fined to domesticated organisms. Among the millions of biolog- ical systems many have wandered from the path of progressive evolution and are on the way to extinction. As with the mo- tions of the heavenly bodies, nature herself has deceived us, or rather she has given us new riddles to read. The motion of species is not like that of the stars, in simple geometrical figures. The evolutionary progress of species is accomplished by the weaving of an intricate fabric of lines of descent through the free interbreeding of the component organ- isms. The simple, normal and typical constitution of a species may be thought of as a huge but simple network of uniform texture. All the organisms are diverse, but the diversity is merely individual and indiscriminate, so that the network has a uniform texture. THE SPECIFIC CONSTITUTION OF LIVING MATTER. Inorganic matter exists in a variety of conditions or physical states, gaseous, liquid, colloidal, crystalline, granular or amor- phous. The properties of matter depend upon these conditions or states quite as much or more than upon the chemical com- position or ultimate nature of the materials of which they are composed. There are laws of gases, liquids and crystals be- cause the different substances behave very much alike in the same physical states. Indeed, the same physical states of dif- ferent substances are generally very much more alike than the different physical states of the same substance. In a similar manner the qualities of living matter are to be associated and described with reference to its various states or conditions. Chemically it is a mixture of water and of small quantities of numerous substances and compounds. Physically it is a jelly or colloid. Biologically it manifests such powers as growth, digestion, motion and reproduction. Morphologically it consists of cells or protoplasmic units with a more or less dif- ferentiated internal structure, and a power to combine or asso- ciate into organisms. For evolutionary purposes the chemical, physical and organic points of view do not suffice. It is necessary to recognize that living matter shows still another unique property, another kind ASPECTS OF KINETIC EVOLUTION 359 of constitution, the specific. A species is quite as concrete a phenomenon as a crystal. Both are collections or aggregates of smaller units, and the units have in both cases definite and necessary relations to each other on which the existence and further development of the crystal or the species depend. It is true that many valuable evolutionary data have been secured from captive or domesticated plants and animals, but the results of this whole class of experiments indicate very definitely that evolutionary phenomena under these conditions are degenerative and not constructive. We are driven back to study the constitution of species in nature, to gain a clear under- standing of the organic conditions which make possible genuine developmental progress, a true organic evolution. No theory or evolutionary interpretation can hope for per- manence which leaves out of account this primary fact that organisms normally exist in large groups of freely interbreeding individuals, the groups commonly called species. Domesticated varieties of plants exist without interbreeding and a few species in nature are supposed to propagate only by vegetative methods, by parthenogenesis or by self-fertilization, but no genus, family or order appears ever to have developed without the association of the individual organisms into interbreeding groups or species. The only exceptions, if any, are among the bacteria and other extremely simple forms of life which have failed to develop either a specialized nuclear structure in the cells themselves or an ability to associate and differentiate to form compound cellu- lar organisms. The reigning popularity of laboratory methods of research may permit small welcome for the suggestion of a method of evolution which requires the extensive equipment of nature and can not be demonstrated in cages or gardens, except by negative results, like those already well known. This disappointment need not continue, however, any longer than may be necessary to perceive that while experiments with domesticated species lose in apparent general significance under the new interpreta- tion, they gain greatly in definiteness. If they do not show us how the fabric of normal evolutionary descent is woven, they at least teach us how it may be unravelled. This knowledge is of 360 COOK great value, not only to help breeders in the making of useful domestic types, but also to students of the general problem. Domesticated plants and animals furnished the most effective arguments for the theory of organic evolution, for although the ancestral wild types of many cultural species are still unknown, and may have become extinct, there can be no doubt that thou- sands of their varieties have originated in domestication, and that similar varieties continue to arise under the eyes of the cultivator and breeder. Domesticated plants and animals have supplied, too, nearly all the materials for evolutionary experi- ments, and it is also with them that evolutionary theories must find, ultimately, their practical application. A false or inadequate theory, though avowedly based on studies of domesticated species, may be quite as injurious to agricultural progress as another drawn from facts ascertained from useless wild species. Any idea worthy of general credence will bear the test of application to both classes of phenomena. A theory is merely a way of thinking about things, and is useful if it enables us to see, or even to suspect, causal connection between facts previously unassociated. One theory is better than another if it brings important facts into relation, and is considered established as a law or doctrine when it accomodates all the facts of the field it was designed to cover. The dis- tinction frequently attempted between " theoretical " and " prac- tical " investigations of evolution is quite fictitious, as in other fields of knowledge. By a curious perversity of language the designation "pure science" is often applied to accumulations of knowledge not yet refined enough to be useful for practical purposes. The talk of discrepancies between theory and practice amounts to a kind of fiction, a euphemistic way of saying that an inadequate theory may not be wholly worthless as an indication of relations not yet adequately understood. For establishing the general fact of variation and thus dem- onstrating the possibility of an evolutionary and continuous creation, the variations which have arisen under domestication afforded the most pertinent and convincing testimony. No biologist now doubts that evolution has taken place and still ASPECTS OF KINETIC EVOLUTION 36 1 continues, but there is, nevertheless, a very wide and very practical divergence of opinion regarding the nature and causes of the evolutionary process. In the study of this question it becomes important to realize that the evolutionary condition of cultural species differs from that of wild types because of the much greater degree of inbreeding to which the former are commonly subjected. The constitution of species has a practical bearing upon agri- culture, not because the domesticated plants and animals have not been studied from an evolutionary standpoint, but for the very opposite reason, that they have been considered too exclu- sively, so that the important differences existing between them and wild species have been overlooked. Ideas drawn from domesticated varieties have been projected into nature at large, and this made it only the more impossible to appreciate the fact that grave differences exist between wild and domesticated groups of organisms. Evolutionary science has gained much from the study of do- mesticated plants and animals, and may gain still more in the future. The objection is only to the use of such studies and results as an exclusive basis of interpretation of the facts of nature. All that happens in domestication may also happen in nature, for domestication is, after all, only a department of nature. It does not follow, however, that nature is fully mir- rored in domestication; the mirror is too small. It shows us only the conditions in which constructive evolution does not take place, even in nature. The recognition of the fact that evolution is a phenomenon depending upon the specific constitution of living matter has been delayed, no doubt, by the difficulties which have been en- countered in the field of taxonomy. In the recent decades nat- uralists have faltered in the task of nomenclature set by Lin- naeus. To merely describe and give names to the millions of evolutionary unit groups of organisms which occupy the sur- face of our planet is a work much too vast for the present re- sources of science. The temptation of weariness has been to shorten it by passing over the apparently useless redundancy of slightly different groups, or by declaring that all is vanity of 362 COOK merely abstract conception, that species do not exist, and can not be defined.1 Those who have not persevered beyond this stage of skepticism and satisfied themselves of the existence of species in nature, can have little use for an interpretation based on the recognition of species as definite entities, consisting not merely of aggre- gates of individual organisms, but also of fabrics of interwoven lines of descent. The difficulty in defining species is the lack of clear percep- tions, not only of the nature and constitution of species, but also of the fact that several diverse types of phenomena are being covered by the word. Under such circumstances a general definition of species, however framed, could afford only a ficti- tious unification of expression, the ideas and implications cov- ered by the term remaining essentially diverse and often quite contradictory. This confusion affords, however, no justifica- tion of a failure to use the term in one or another of the explicit senses of which it is capable, nor of a refusal to define the usage of the term in any particular connection. The difficulty of defining the term species has arisen mostly from the fact that the phenomenon is a physiological one, whereas the general supposition has been that it is morpho- logical. The idea that species are " founded on identity of form and structure," as the dictionaries say, is still widely prevalent, and is one of the tenets of evolutionary belief upon which Professor De Vries especially insists. The impracticability of a morphological definition of species arises from the fact that it is impossible to set definite limits to the extent of the variability or diversity which is to be permitted in the species. Identity of form and structure makes an excellent definition ; the objection to it is that no such species seem to exist in nature, or as Professor De Vries says, " * * * purely uniform species seem to be relatively rare." 2 In some groups 1 Thus a recent defender of the mutation theory of De Vries has declared : " If it is really true that De Vries does not know what constitutes a species, then, indeed, we find our faith in his work thereby increased. Who, indeed, except the makers of dictionaries, does ' know what constitutes a species ' ? " This method of reasoning was very popular in mediaeval times and was then, reduced to the neatly pious formula: " Credo quia absurdum." 2De Vries, H., 1905. Species and Varieties, 64. ASPECTS OF KINETIC EVOLUTION 363 all the members of the species are closely similar, but in others they may be extremely unlike, as when the specializations of sex and polymorphism have been developed. There is no need, however, that we define species as a morphological term, since species are not caused nor constituted by the likeness or unlike- ness of the component organisms. Indeed, it is unlikeness rather than likeness that conduces to the prosperity of the species. The species in nature is constituted by the fact that the com- ponent individuals breed together. For evolutionary purposes a species is a group of interbreeding organisms ; nothing more is required, nothing less will suffice. Species are units of organic evolution ; organisms continue to exist and to make evo- lutionary progress only in large groups of freely interbreeding individuals. Groups of organisms which do not interbreed are no longer species ; they no longer have the typical and essential evolutionary constitution of living matter. Whether the individuals are alike or different does not in the least affect the specific unity of a group if the organisms are associated in nature on a basis of free interbreeding. If the groups have ceased to interbreed, Avhether by reason of geo- graphical barriers, or of structural or instinctive incompatibility, they are no longer a unit of evolution, no matter how close the external similarity may appear. Natural species are not the only groups of organisms to which the name is applied, but since all other so-called species are mere parts or fragments of natural species, a recognition of natural species must precede a true appreciation of the more or less artificial subdivisions of species. These evolutionary facts are quite independent of the old taxonomic idea that the limits of species could be determined by ascertaming whether the animals or plants can interbreed. The evolutionary question is whether they do interbreed. Groups able to interbreed perfectly will still follow divergent courses of evolution, if kept apart. On the other hand, the failure of the extreme members of the same species to inter- breed would not destroy the unity and coherence of the group.1 1 Cook, O. F., 1905. The Evolutionary Significance of Species. Smith- sonian Report for 1904. 364 COOK The exclusion of the domesticated plants and animals from use as illustrations of the true methods of evolution may appear to withdraw the subject from the consideration of all who do not have intimate acquaintance with' species in nature. There remains, however, an excellent and very familiar example of evolutionary conditions, that of man himself. The genus Homo has achieved in a relatively brief period a wide divergence from its simian relatives. This progress in development has been coincident with the achievement of a world-wide distribu- tion and with free interbreeding throughout the area of distribu- tion, except as hindered by geographical barriers. Moreover, a further close analogy is to be found in the development of the human individual personality by a complex network of contacts with other members of a social group. Without such social contacts the intellectual development was limited to automatic instincts ; with socialization new lines of evolution became pos- sible, just as conjugation opened the road to the development of compound organisms, and the further various stages of advance in prolonged conjugation made possible higher and higher types of cellular structures. LONGITUDINAL AND TRANSVERSE SECTIONS OF SPECIES. Longitudinal sections of species show differences along lines of descent. They include what are commonly called life-his- tories, based on studies of the progressive changes of form and of methods of existence by which individual organisms follow each other in lines of descent. Transverse sections of species show differences and relations between lines of descent, that is, the internal bionomy of the species. The objects of study are not the methods of develop- ment or the physiology of individuals as such, but the nature and relations of the different kinds of individuals which exist in the species. The individuals of a species which are alive at any one time may be thought of as affording a cross-section or end view of the network of descent. Some of the facts of the constitution of species can be under- stood best from longitudinal sections, some from cross-sections, and many can be best thought of by keeping both aspects of the network in mind. ASPECTS OF KINETIC EVOLUTION 365 DIVERSITY IN LENGTHS OF CONJUGATE PERIODS. The patterns of longitudinal sections of the networks of de- scent of different species are determined by the longevity of the individual organisms. In popular language it might be said that the generations of some species overlap while those of other species do not. Many species, both of animals and of plants, are strictly annual. All of the adults die in the fall, and the species exists in the winter only in the form of eggs, spores or seeds. These hatch or germinate in the spring and all the new individuals grow to a simultaneous sexual maturity, interbreed, reproduce and die. All the members of the species are in nearly the same condition at the same time and the figure of descent is simple and regular. A few species, such as the bamboos among the plants, pre- serve this complete simultaneity, although living through a con- siderable series of years. Flowers and fruits may be produced only at rare intervals of two or three decades. All the plants of the species reproduce at the same time and then die. But in nearly all groups the lengthening of the life of the individual organism means the overlapping of the generations and the simultaneous existence of many different forms or stages of the species. Such a statement is not adequate, however, for a scientific description of the complexities of overlapping descent ; for the word generation has been used with a great diversity of mean- ings. In the lowest unicellular organisms each independent cell-individual is a generation. In the next stage, where the cells are joined into simple and relatively undifferentiated struc- tures, the word generation may well denote the interval between two successive conjugations, or rather the structure which is built up between the ending of one conjugation and the ending of the next. But even this definition fails us as we go higher in the scale of existence and find plants and animals which build two or more organic structures between successive conjugations. In some cases there is a succession of two kinds of cellular structures, one structure being built up before the formation of the sex-cells, before conjugation commences, and another structure after conjugation has commenced. The former is 366 COOK built of simple nonconjugate cells, the latter of double or con- jugate cells. The nonconjugate structure corresponds to the " generation" of the simpler types of organization. The con- jugate structure is a new feature intercalated into the previous life-cycle, which it often completely overshadows. The con- jugation period of many organisms, and especially of the highest groups, both of animals and of plants, is now very much longer than the part of their life history which corresponds to a whole generation in the lower groups. For tracing homol- ogies between the higher and the lower groups it is still pos- sible to talk of the period between conjugations as a gener- ation, but most of the generation is now occupied by the conjugation period, the life-time of the double-celled phase of organization. This corresponds merely to the fertilized egg-cell or oospore of the lower algae which do not build up any struc- tures of conjugate cells. In other cases, which are properly to be called alternation of generations, the diversity of the two interconjugational forms has been brought about by vegetative propagation, which replaces or supplements the sexual reproduction of the species. Alter- nation of generations, that is, of two forms of organic individuals in the same species, may take place either in the conjugate or in the simple or nonconjugate period of the "generation." Thus in the mosses and liverworts vegetative propagation is fre- quent in the simple-celled phase, while in the ferns and flower- ing plants it appears in the conjugate period. Vegetative pro- pagation is often described as a purely asexual process, but this is not true of the higher plants, since the conjugate phase is wholly a sexual phenomenon, a part of the sexual process of conjugation. It may therefore be held that the term generation, as popularly used with reference to the higher plants and animals, does not correspond to what is meant by generations among the lower groups. The period of the life-history which constitutes a gen- eration among the more primitive types of life is so brief as to remain practically unnoticed among the highest. Conversely, the conjugate period which is so short and unimportant as not to complicate the question of generations in the lower groups is ASPECTS OF KINETIC EVOLUTION 367 lengthened to cover nearly all the activities of the species in higher types of life. Among the lower groups the overlapping of the generations appears to be a mere coincidence and serves no important evo- lutionary purpose, but among the higher types it is a condition of the utmost significance, since it has permitted the develop- ment of parental instincts and of the numberless devices and habits by which the eggs or seeds or the young individuals are protected and nourished through periods of helplessness. The lengthening of the embryonic and juvenile periods has been necessary to permit the development of large and highly special- ized organisms. The overlapping of the generations is also a prerequisite for the development of social habits and instincts, and especially in the transmission of the postnatal inheritance on which the development of human culture and civilization depends. Civilization has been developed and has persisted only among those races in which the family unit of social organ- ization was maintained, so that the children secured the advan- tage of long and intimate contact with their parents and were thus able to acquire, transmit and accumulate in the race the collective experience and progress of the component individuals and families. Thus the aborigines of tropical America who live mostly in separate and isolated families have built up numerous primitive civilizations, while the natives of tropical Africa who live only in villages have never developed civiliza- tions. Indian children are the constant associates and helpers of their parents while the children of an African village are herded among themselves in little troops or squads like the street waifs of our slums. Even our highly developed systems of formal education have this serious defect and danger, that they tend to disconnect the generations, and to throw the young into premature and reactionary forms of social organization instead of permitting them to grow gradually into their normal places in the general fabric of the community. DIFFERENT TYPES OF CELLULAR ORGANIZATION. The complexity of the constitution of species can not be fully appreciated unless it be kept in mind that each individual of all 368 COOK the higher types of life is itself a compact system or colony of cellular organisms, and that these compound units are not only different as to the aggregate cell-individuals, but there are dif- ferent kinds of cellular organizations. Not only does endless diversity exist among the unicellular or single-celled types of life ; there are also different manners and degrees of cell-asso- ciation to make up the multicellular types. If the cells of the colony-individuals are alike, the organism is called isocytic, if unlike heterocytic. If the cells which associate have no separating cell-walls the organism may be described as plasmodial, as in the Myxomy- cetes and in such alga? as Caulerfia and Acetabularia. If the cells have the form of long slender filaments the organism is described as hyphal, as in the fungi ; if built of definite cell blocks it is called cellular, in the strict sense. The fourth or highest type, found in the animals, combines the other three. Some cells remain quite free and unattached, like the red and white blood corpuscles ; some tissues are still plasmodial, others hyphal, while still others, and these in the majority, have definite cellular structure. Finally, the colony-individuals differ in being built of cells which are not conjugating (agamic cell-structures) or of those which are in conjugation (conjugate cell-structures). Of the latter there are two types, the first is that shown by the higher fungi which build colony-individuals of binucleate cells, formed before the nuclei have fused in conjugation (apaulogamic cell- structures). The second type of conjugate structure is that of the higher plants and animals whose bodies are built up of cells with the nuclei fused, but with a double number of chromosomes (paragamic cell-structures). These facts are capable of a very definite graphic represen- tation in our ideal longitudinal sections of specific networks of descent. Double-celled structures are the conjugate product of two lines of descent and their existence is to be shown in our diagram by double, closely parallel lines. The network which represents the method of descent of intermediate groups, such as thearchegoniate plants (liverworts, mosses and ferns), may show single and double lines in almost equal proportions. Primitive ASPECTS OF KINETIC EVOLUTION 369 groups may show only single lines, higher groups only double lines, except at the actual points of junction where conjugation takes place.1 In alternation of generation and metamorphosis the organism changes its external form without altering the figure of descent. Alternation of generations, like the differentiation of separate sexes, exists in simple-celled as well as in double-celled organ- isms. The phenomena are of an entirely different and minor order of significance compared with the diversities of the dif- ferent types of cellular structure. Wonderful as the changes are, they are still of a merely morphological and adaptive character and do not indicate new evolutionary departures of the scope of the double-celled structures. SPECIFIC CONSTITUTIONS MODIFIED BY SPECIALIZED HETERISM. There are two principal groups or kinds of specific constitu- tions which can be studied or thought of as cross-sections of the networks of descent. These two series of special types of species arise through two forms of specialization of methods of descent. Instead of remaining uniform or homogeneous throughout, the network of descent becomes variously subdivided or separated into subspecific strands. The first form of subspecific differentiation consists in special- izations of heterism, that is, the establishment within the species of definite forms of diversity of descent, so that individuals are not merely different individually, but fall into two or more groups regularly distinguishable by definite characters. These groups are not formed by isolation, and their existence does not interfere with interbreeding, but usually has the contrary effect of encouraging or compelling interbreeding, since the members of the same group may be unable to interbreed with each other, but are specially adapted for interbreeding with the members of the other group or groups of which the species is composed. SPECIES WITHOUT SPECIALIZATION OF HETERISM (ARROPIC). The diversity of normal symbasic descent remains miscel- laneous and unspecialized. The individuals may be more or less 1 Diagrams of networks of descent in the various types of double-celled struc- tures have been given in another place. Bulletin Si, Bureau of Plant Industry, U. S. Department of Agriculture. 370 cook obviously different, but the differences are fluctuating or com- pletely intergraded, so that no definite alternatives of descent appear, and no distinct subspecific groups are indicated. Individuals are all similar, equivalent and bisexual or her- maphrodite. None of the vertebrate or arthropod animals show this condition, but it appears to be very common among the lower animals and among plants. Species in which there are no specializations of heterism, no differentiated paths of alterna- tive descent, may be called arropic species. The arropic condition is not merely synonymous with herma- phroditism, through all arropic species are bisexual. The her- maphroditism of the lower groups of animals and of plants is a normal condition incidental to their more primitive organization. Among the higher groups which have attained sexual differ- entiation hermaphroditism has reference more definitely to ab- normal cases of bisexuality. The arropic condition is also more definite and restricted than bisexuality, since organisms may be bisexual and still manifest some of the following forms of alter- native heterism. SPECIES WITH SPECIALIZATIONS OF HETERISM (ROPIC). Specializations of heterism exist, and definitely alternative routes of descent are followed by different individuals. The individual members of species fall into distinct groups, but not as the result of segregation or of differences of environmental conditions. The group differences are usually such as to facili- tate or to compel interbreeding between the groups. The attainment of the ropic condition marks an important stage in the evolution of a species, very favorable, apparently, to its further development and to the greater and greater exten- sion of the heteric specializations. The distinction is entirely concrete and practical, but there seems to be no suitable and convenient English word by which to designate it. The expres- sions alternation and alternative have been used too widely al- ready, and would increase the confusion now existing as the result of identifying alternation of generations with phenomena of entirely distinct nature, such as the different kinds of cellular structures. ASPECTS OF KINETIC EVOLUTION 371 Subsexual Species. — A species consisting of bisexual organ- isms divided into subsexes, that is, into groups differing in one or more characters, but not showing special adaptations to secure cross-fertilization. The first stage of specialized heterism is represented by spe- cies which include two or more types or forms, merely for the sake of the diversity, as it were, and with no sexual diversifi- cation, that is, no adaptations, for securing cross-fertilization between the two forms. The differences appear to be of the same nature and to have the same symbasic utility as secondary sexual characters, but the utilization of them is still left to chance. Examples of subsexes are probably to be found in such species as Verbascum blatlaria, Viola hicolor, and others in which plants of different castes live together indiscriminately. Antidromous or right-and-left-handed plants like cotton and Casltlla, might also be recognized as affording instances of subsexual differentiation. It often happens in zoology that the sexes of the same animals are at first described and named as two distinct species, but after their true relations have been ascertained one of the sup- posed species is, of course, rejected, no matter how diverse the sexes may be. Similarly, these subsexual forms need to be taken into account by the taxonomist. The criteria commonly applied to determine specific distinctness are not adequate, since it is possible for constant differences unconnected with sexual diversity, to exist inside the same species without in any way justifying the taxonomic subdivision of the group on the usual basis. There is, however, no reason why any established type of diversity like these subsexes should not be named and de- scribed separately, just as the sexes are treated separately when their characters are different. Botanists are acquainted with numerous instances of diversity among the members of species which may prove to be subsexes ; though it is also possible that the differences may belong to species which closer study may distinguish. Thus there are species of Actcea which have the berries either waxy white or crimson, and in about equal quantities. Numerous species of Delphinium have the flowers either pink or blue. In species 372 COOK of Aconitum purple and creamy or greenish white flowers are described. Pink flowers also appear occasionally as definite variants of white-flowered species of Achillcea. Semisexual Species. — A species consisting of bisexual organ- isms divided into semisexes, that is, into groups differing in characters which conduce to interbreeding between the groups. This is the condition reached by many species in which the individuals are all bisexual, but differ among themselves in char- acters which insure, or at least facilitate, cross-fertilization. In the well known instance of Lythrum there are three castes of plants with short, medium, and long styles and filaments, and three different kinds of pollen grains and stigmatic papillae. A long-styled plant produces only short and medium stamens, and must be fertilized by pollen from long stamens, to be found only on other plants. The semisexes of the primrose were described by Darwin. Similar conditions are known in Oxalis, Houstonia, and many other genera. Among plants, at least, it might appear that semisexual con- ditions are more advantageous than the next stage of completely differentiated sexes. Cross-fertilization is secured, but at the same time all individuals may produce seed, and not merely half of them. That complete sexual differentiation has been attained notwithstanding, and in so many different groups, affords an intimation of the importance of symbasic heterism in the structural economy of organisms. The fact loses none of its significance if we reflect that the complete separation of the sexes in plants reduces by half the facilities of the species for producing seeds. All individuals being stationary, the males can contribute to the welfare of species by none of the accessory habits which have been so richly developed among the animals. Indeed, it is by no means unlikely that the tendency of selective influence on many plants has been to keep them in the semi- sexual condition, sexually differentiated only far enough to secure cross-fertilization, but not far enough to preclude the production of seeds by all individuals. Sexual Species. — A species consisting of unisexual organ- isms, or divided into two sexes, male and female, so that inter- breeding between the sexes is necessary to reproduction. ASPECTS OF KINETIC EVOLUTION 373 The complete separation of species into two sexes is the con- dition obtaining in all the higher animals, both vertebrates and arthropods, as well as in many of the lower animals, and in numerous plants. It has been found recently that even among the moulds and other lower fungi the plant body, or mycelium, is of two kinds, and that spores are produced only when these are brought together. Secondary sexual characters are of two kinds, or may be so considered : (i) Those which are accessory to reproductive processes, or assist in caring for the seeds, eggs, or young, such as the mammas of the higher animals ; (2) those which are merely the result of accumulation of differences which add to the heterism or internal diversity of the species, such as the manes, beards, tail-feathers or sexual differences of color or form which are of no use in reproduction or in the environ- mental relations of the species. The environmental uselessness of many sexual differences is an obvious and well known fact. Not only do the two sexes generally occupy exactly the same environment with equal suc- cess, but the presence or absence of many sexual character- istics may have no practical significance for the individual. Some varieties of mankind are beardless ; some have beards only late in life, and some have beards in early manhood, but cut them off without appreciable detriment. The uselessness of such characters is shown even more strikingly in certain species of beetles. Some of the males are scarcely distin- guishable externally from the females, while others have the head or thorax fantastically modified by the growth of long, heavy, antler-like processes. It is easy to understand that for all the males to be thus encumbered might be a serious handi- cap to the species. It may be that selection will help to explain why such fea- tures commonly pertain to the male sex. Great diversity among the females would interfere with recognition by males unless their instincts were modified in a corresponding manner. More- over, variation is the more practicable in the male sex because the extent of the coordination necessary among the bodily or- gans is not so great. Variation, which in the females might 374 COOK have occasioned serious functional derangements or might have too greatly increased the difficulties of existence, can be toler- ated by the males without injury to the species. That secondary sexual characters are often so completely without function, in the ordinary sense of the word, does not mean that they are of no value to the organism. With refer- ence to the environment they are often worse than useless, but in the physiology of descent they may have an important func- tion. The existence of two sexes doubles, as it were, the sym- basic effect of cross-fertilization, by permitting the accumulation of two sets of variations, a second reason for the more rapid progress made by sexually diversified organisms. What has been called organic evolution has been thought of too exclusively from the environmental side. Evolution has an internal as well as an external function ; it has a bearing upon the quality of organisms, as well as upon quantity. Species are advantaged not only by characters which give them a wide range and permit the propagation of large numbers, but it is of equal importance that the vitality of the species be maintained through the provision of adequate diversity of descent, as as- sured by sexual specialization and by the access of new varia- tions. The doctrine of sexual selection was invented by Darwin to explain the so-called secondary characters, differences admit- tedly useless from the environmental standpoint, the two sexes of a species being subject, generally, to identical external con- ditions. And yet there is everywhere manifest a tendency to the further accentuation of sexual diversities, which are by no means confined to man, or to the higher animals in which esthetic instincts have been attained. Viewed as specializations of heterism, secondary sexual char- acters have an obvious and general utility, though of an internal nature. A species with two separated sexes is the stronger because it can accumulate two lines of variations. Symbasic interbreeding becomes, as it were, doubly effective, and the stimulus of diversity can be utilized for a much longer period than if the character were to spread to all the members of the species. If the present interpretation of the facts be correct, we have ASPECTS OF KINETIC EVOLUTION 375 in the familiar phenomenon of sex an example of a fundamental evolutionary principle which has thus far escaped formal recog- nition. Heterism is a concrete property or requirement for con- structive evolution, though left quite out of account in theories which have thought to explain organic development by external influences of environment, or by internal "mechanisms of heredity." Sex specialization in species corresponds to paragamy in cells ; the sustained diversity of the associated sexes is curiously analogous to the prolonged separation of the parental chromo- somes. Sexuality supplements paragamy, and both serve the same purpose of increasing the vitality of the individual organ- isms and the coherence of the specific networks of descent. Superscxual Species. — A species consisting of organisms of two sexes, but with one or both sexes again subdivided into two or more kinds of individuals. That the uses of the diversities of the sexes are not limited merely to the reproductive functions, is well shown by the fact that specializations of heterism are sometimes carried beyond the stage of definite sexuality. Thus there are, among the sexually differentiated higher animals and birds, numerous instances of the existence of two color-forms, indifferently intermingled, but not intergraded. It has been found, for example, that there are in eastern North America two kinds of screech-owls, red and gray, which are not separated geographically or in breeding. The following reference to the occurrence of leopards of two colors in the Malay region may serve as a sample of many similar observations among the mammals. " Man}" of the hunters I have met, and some of the authors I have read, appear to consider the black leopard a distinct species, but it is simply a freak of the ordinary spotted leopard, just as the silver and the black fox are freaks from the common red. In a litter from a red vixen I have seen a silver among red pups ; and I met a man in the jungle where lower Siam meets the Malay Peninsula who had found a black among the spotted leopard's cubs, upon which, however, the spots, of course, are not very clearly defined until they become older." ..." I noticed after I got its pelt off, that in the sun it had 376 cook a kind of watered silk appearance, as a result of the deeper black of the spots, which, though invisible, were really there just the same." l In a similar case of supersexual dichromatism in a chrysomelid beetle experiments showed that the two color-forms could be separated and established as uniform varieties by selective breeding.2 The mating of black individuals produced only black offspring in the first generation, while matings of spotted individuals continued to give a proportion of black offspring until the third generation. SPECIFIC CONSTITUTIONS MODIFIED BY RESTRICTED DESCENT. This is the second form of diversity of constitutions revealed by cross-sections of networks of descent. Unlike the specializa- tions of heterism, the members of groups formed by restricted descent do not, of course, breed together, for it is in this that the restriction of descent consists. The specializations of heterism are in accord with the evolutionary advancement of the species, but the groups formed by restricted descent are removed from the conditions of free interbreeding and of normal evolu- tionary progress. They represent, instead, the different stages of a process of deterioration. Symbasic Species. — Species with descent unrestricted, con- sisting of large numbers of diverse individuals freely inter- breeding in a broad, continuous and regular network of descent. A species is not merely an aggregation of organisms, whether alike or different ; the organisms are connected by a completely interwoven fabric of lines of descent. Such plants as Portulaca oleracea, Poa pratensis and Ceratodon purpureus, may serve as examples of very widely distributed symbasic species. Porric Species. — Species made up of partially segregated subspecies. The cross-section of the network of descent, instead of showing a rounded or regular form, is irregular, or partially subdivided into arms or branches. Widely distributed species, but locally diversified, like the 1 Whitney, Caspar, 1904. Outing for April, p. 14. 2McCracken, I., 1905. A study of the Inheritance of Dichromatism in Lina Lapponica. Journal of Experimental Zoology, 2 : 117. ASPECTS OF KINETIC EVOLUTION m European Helix hortensis, afford the best examples of this type of intraspecific diversity. The quail, or Virginia partridge, a non- migratory bird widely distributed through eastern North America from New England to Guatamala, shows many local subspecies connected by series of imperceptible gradations. The sugar maple of eastern North America has several geographical sub- species. Stenic Species. — Species consisting of stens, that is, of nar- rowly segregated subspecies, domesticated varieties, or breeds, propagated by sexual reproduction. As a result of propagation by narrow breeding, the individual members of a sten are much more nearly uniform than those of normal symbasic species, or even than those of geographical subspecies. As purely stenic species may be mentioned those which do not exist any longer in the wild state, but are made up of many local domesticated varieties. The domesticated animals fall here, except as they may represent hybrids of dif- ferent wild species. Of domesticated plants the Indian corn or maize is the best example, since it has retained a complete system of cross-fertilization, which many domesticated plants have lost. Very small, closely localized natural species, like the remark- able Hawaiian land-snails upon which Gulick has based his theory of evolution by isolation, represent essentially the same condition of restricted descent as domesticated stenic varieties. Linic Species. — Species composed of separate, parallel or slightly diverging lines of descent, propagated by autogamy or parthenogenesis, and not united into a network. Wheat and barley are perhaps the most conspicuous examples of linic species among domesticated plants, though many other species are autogamous, with more or less consistencv- Strict line breeding is not possible, of course, among the sexually differentiated higher animals, but is sometimes approached by what is called in-and-in breeding of closely related individuals. Line-bred organisms are extremely uniform, even more so than stens. Self-fertilization involves only the combination of gametes of the same origin and probably of very nearly identical nuclear configuration ; at least there is even less varia- tion. Linic species occur in nature as in the well-known in- 378 cook stances of Hieracium upon which Nageli based his theory of evolution in a definite direction. The persistence by partheno- genesis of the individual differences of transplanted specimens was accepted as proving that variation held to definite directions. Likewise De Vries has made use of linic autogamous species of Draba to illustrate his conception of elementary species. The uniformity and stability of the line-bred plants has been taken to represent the normal condition of species, and the in- ference has been made that the species recognized in nature by taxonomists are generally composed of similar independent units, the effect of the method of propagation, to resolve the spe- cies into separate lines of descent, being left out of consideration. Clonic Species. — Species consisting of separate lines of de- scent continued by vegetative propagation alone. Clones, like lines, are propagated from single individuals, but by vegetative processes only, so that variation is almost completely avoided. Nevertheless, even vegetatively propa- gated plants are not completely uniform. Clonic groups of the same origin often show fine gradations of diversity, and occa- sional mutative variations are known. Clones do not exist, of course, among the higher animals, but they areexceedingly numerous among plants. Several domes- ticated species now exist, as far as known, only in this form. The horse-raddish, sweet-potato, banana, arracacha, yautia and taro may be mentioned as seedless plants, but large numbers of others are nearly seedless or have varieties which are seedless. THEORIES OF EVOLUTION BY RESTRICTED DESCENT. It is a noteworthy fact that the earlier theories of evolution, including those of Darwin, Nageli, Gulick and De Vries, have been based upon one or another condition of restricted descent. The kinetic theory is the only suggestion of a method of evolu- tion applicable to conditions of unrestricted descent. The pre- disposition to see in restricted descent ideal conditions of evolu- tion has been strengthened, if it has not been wholly supported, by the fact that it is only in restricted descent that the traditional ideal of heredity can be applied. Only narrow-bred organisms afford even an approximate identity of form and structure. ASPECTS OF KINETIC EVOLUTION 379 De Vries, Gulick and Nageli have given their chief attention to extreme forms of restriction, like those of Draba, Achatinclla and Hieracium. Darwin kept much nearer to the consideration of natural conditions, though his doctrine of selection implies that evolutionary progress depends entirely upon the plan of causing species to change by restricting the descent of the com- ponent individuals. In the kinetic theory, it need scarcely be repeated, the result of selective restriction is not evolution, but specialization. The evolutionary motion would still take place if the selective restrictions of descent were not imposed. COMBINED FORMS OF SUBSPECIFIC DIVERSITY. Modifications of the constitution of species by specializations of heterism do not interfere with the attainment of the other form of diversity by restricted descent. Thus a sexual species may be partially segregated into geographical subspecies or may be narrowed still further into the stenic condition of domesticated varieties and breeds. Linic and clonic subdivisions of sexually differentiated species do not occur, of course, among the higher animals, being limited to the lower groups and to plants which have the power of sexual propagation or of parthenogenetic de- velopment. But even among the cultivated plants it does not appear that any sexually differentiated species has been resolved completely into the clonic condition. There are large numbers of clonic female varieties of figs and date-palms, but the male trees are usually recruited from chance seedlings, so that the network of descent is not entirely destroyed. The female half of the species is represented by vegetatively propagated clones, but on the male side miscellaneous individual diversity remains. The existence of restricted subspecific groups may not inter- fere in the least with the maintenance of a normal specific net- work of descent. A widely distributed symbasic species may have a few porric subspecies as a result of the partial isolation of particular localities. Special conditions, such as an alpine climate, might restrict a part of a species to linic or clonic propagation while the remainder retained fully symbasic condi- tions of descent. Through the fabric of broadly diversified descent there may run narrowly compact strands composed of 380 COOK linic or clonic individuals, which no longer share the symbasic interbreeding of the group and afford no true criterion of the conditions under which evolution goes forward. Just as most planets are attended by satellites, so species are sometimes found to be supplemented by small subspecific adjuncts, little species-like groups of organisms which some have taken for new or incipient species, but which stand in a permanently sub- ordinate or retrograde relation to the evolutionary part of the species. LIMITATIONS OF CLONIC PROPAGATION. Vegetative propagation, whether in nature or in domestication, appears to conduce always to seedlessness. Some have thought to explain this fact by reference to the superiority of the asexual over the sexual propagation. This reasoning is scarcely ade- quate, in view of the fact that much larger numbers of species have retained their capacity of producing seeds, though regu- larly supplementing the sexual by the vegetative propagation. The greater probability is that the decline of sexual fertility in vegetatively propagated types is a symptom of deterioration, just as sterility is a frequent characteristic of abnormal vari- ations or of hybrids. The formation of the sex-cells, as we now know, is a highly specialized and complicated process, and it is easy to understand why it should be the first of the physiological functions to become deranged and inefficient. It is known also, from the behavior of hybrids and mutations, that vegetative vigor has no direct relation or apparent connection with reproductive vigor. Indeed, sterile hybrids and mutations often show great and notably superior strength and longevity, due, we may suppose, to the stimulation which attends new variations. This con- sideration may also explain why clonic and linic species usually appear to consist of definite groups of closely similar individuals. These groups may have originated by individual mutative vari- ations of notable vegetative vigor, which have on this account survived or crowded out the weakening survivors of the original symbasic species or other variations less recent or less vigorous. The disastrous effects of inbreeding among the higher ani- mals have been known for centuries, and are taken into account ASPECTS OF KINETIC EVOLUTION 38 1 by all breeders. That the same principles apply to plants, has remained in doubt for two reasons : (1) The much less com- plex organization and less specialized tissues of plants render many of them less acutely dependent upon cross-fertilization. (2) The plants which have been longest under cultivation are not grown for their seeds and are propagated asexually, so that their decline in reproductive fertility has not diminished their economic value. No plant valued for its seeds has been propagated other than from seeds for any considerable period.1 Numerous tropical root-crops and fruits, such as the sweet-po- tato, yam, agave, sugar-cane, banana, pine-apple, and bread- fruit have been grown for thousands of years from cuttings, prob- ably without the interposition of a single seedling generation. In a sexually propagated species inbreeding would have led long since to extinction, but these clonic varieties are still ex- tremely vigorous. Nevertheless, such species do not form a real exception to the rule of deterioration under inbreeding, since a very large proportion of them, belonging to many and very diverse families, have shown this tendency towards seedlessness. The reduction or elimination of the reproductive parts has been ascribed by some to selection, and by others to a supposed biological law of paucity which causes useless parts to disap- pear. No basis of fact has been shown, however, for either of these explanations ; unassisted nature supplies us with instances like Sphagnum and Lunularia to which neither would logic- ally apply, but which would be well accommodated in the view that continued asexual propagation, like other forms of isolation, weakens the reproductive powers. This law would also explain why the absence of sexual reproduction ap- pears only as the character of aberrant species or genera, and has not been able to persist for a period long enough to permit the differentiation of organic groups of higher systematic rank. Botanists seem not to have ascertained the existence of any wild phanerogamous plant which is always and everywhere seedless. 'Apparent exceptions to this rule appear only among trees, such as the almond and the pistache, where the normal long life of the individual may be thought of as lessening the period of vegetative propagation, if counted by generations. 382 COOK The opinion has long existed among horticulturists that varie- ties of fruit trees tend to deteriorate, but a biological explana- tion has been lacking thus far. The most prominent horticul- tural writer to defend such a view is Burbidge, who holds that budding and grafting are artificial and unnatural processes, for which propagation by rooted cuttings should be substituted. The analogy of the seedless tropical root-crops indicates that the use of cuttings would afford no protection against the grad- ual reduction of fertility, though the suppression of seeds in fruit trees may not be an undesirable symptom, except when it is accompanied by a deterioradon in quality. Only a few hor- ticultural varieties have been propagated as clones for more than a century, but the advance of sterility has already become ap- preciable to nurserymen, who are careful to plant seeds from seedling trees, in the belief that these germinate better and pro- duce more vigorous stocks than the fruit of grafted clonic varieties. That superior varieties are commonly deficient in vigor is thus explainable without reference to any special perversity of nature ; such varieties may owe their reproductive debility to the fact that they have been more carefully and persistently propagated without crossing. Some varieties of peaches, for example, yield a very small percentage of viable seed. In France many attempts to secure seedlings of the "Alexander" have failed. This variety and the very similar " Amsden " appeared about the same time and are supposed to be seedlings of " Hale's Early," a variety also notably deficient in reproductive fertility, since only about ten per cent, of the seeds germinate. The seedlings of " Hale's Early" are also, as a general rule, very diverse, without close resemblance to the parent or to each other. The variety called " Hill's Chili " affords an instructive contrast, in that practically all the seeds germinate and about ninety per cent, of the seedlings come true to the parental type, leaving about ten per cent, of variations.1 Obviously, the evolutionary status of these two varieties is very different ; one is entering upon the stage of mutative aber- 'For these interesting facts I am indebted to Mr. William A. Taylor, of the United States Department of Agriculture. ASPECTS OF KINETIC EVOLUTION 383 ration, while the other is approaching that of complete sterility. Horticulturists have not uncommonly believed that the longer the succession of " grafted generations " of tree fruits the greater the likelihood of deviations from the type of the original seedling, but this idea seems not to have received scientific consideration or support, perhaps because it appeared to contradict the opinion of Darwin1 and many other evolutionary writers who have held that characters can be permanently " fixed " by inbreeding, or close selective segregation, of which propagation by cuttings may be taken to be the extreme form. The kinetic theory of evolution permits us to understand, however, that the "fixity" to be secured either by inbreeding or by asexual propagation is only relative, and that its result in both cases is to predispose the organism to abrupt variations and reproductive debility. ORIGIN OF LINIC AND CLONIC CONDITIONS. The occurrence of self-fertilization , parthenogenesis, and vege- tative propagation in nature has undoubtedly caused many writers to suppose that these methods of descent represent truly normal evolutionary conditions. Indeed, no abnormality need be charged in the many cases where the species maintains at the same time the normal network of descent by sexual repro- duction with free interbreeding. The abnormal condition super- venes when the species loses its network of symbasic descent and is resolved into disconnected lines. Such a condition may result whenever the normally sexual and symbasic reproduction becomes less effective than autogamous or purely vegetative methods of propagation. Thus, in such little plants as Draba and Viola, which have to avoid the competition of larger neigh- bors by blossoming early in the spring, the non-symbasic methods of propagation take on great importance, for insects are scarce and the weather often so inclement as to completely prevent the transfer of pollen. Similarly, in alpine and arctic conditions, vegetative propaga- tion is much safer, and usually much more successful than sex- ual reproduction. The short and treacherous seasons often pre- vent the ripening of seed. The formation of apogamic bulblets 'The Effects of Cross and Self-Fertilization in the Vegetable Kingdom, p. 27. 384 COOK instead of flowers is frequent among the saxifrages and other Arctic plants, though many similar instances are known in natives of temperate and tropical regions. Wheat and barley, and to a less degree several other domes- ticated plants, have been unconsciously selected towards autog- amy in a similar manner, by being cultivated far to the north of their original habitats. In unfavorable seasons only the autogamously fertilized seeds would ripen. The wild relatives of all these plants, so far as known, have facilities for cross- fertilization. That autogamy and other forms of restricted descent conduce to the breaking up of species into small subspecific groups, is well shown among the cereals. The rye plant has retained and even accentuated its provisions for cross-fertilization, and has kept its position as a relatively normal coherent species, instead of falling apart into distinct varieties. Cross-fertilization has also been fully maintained in the corn plant, but here the large size of the seeds and their compact grouping on the ears greatly facili- tate selection, and have favored the establishment of many local varieties. RELATION OF LINIC TO CLONIC PROPAGATION. The fact that reproductive fertility deteriorates more rapidly than vegetative vigor, when organisms are placed under condi- tions of restricted descent, is to be correlated with another phe- nomenon, discovered by Darwin, that autogamous fertilization is sometimes superior to more miscellaneous methods of narrow inbreeding. This fact has been generally accepted to mean that autogamy and heterogamy are both normal evolutionary conditions. In the kinetic interpretation it does not appear that autogamy is a truly normal and progressive state. The superiority of strict autogamy over more miscellaneous inbreed- ing appears explainable by analogy with parthenogenesis and vegetative propagation. All three processes can be viewed as methods of postponing deterioration from restricted descent, by omitting the nuclear readjustments which are required in normal sexual reproduction. When diversity of descent is no longer sufficient for normal readjustments, degeneration begins, in the form of mutative variations. These usually fall below the ASPECTS OK KINETIC EVOLUTION 385 parental standards, or.at least diverge from them so seriously as to injure the commercial value of the crop, as strikingly shown in the tobacco varieties studied by Mr. A. D. Shamel.1 Seed produced by autogamous fertilization yields plants of very much greater uniformity, and it is in this fact that their superiority lies. The plants were not better, as individuals, than some of those produced by the more miscellaneous breeding, but the tendency to degenerate variation had been avoided, or at least postponed. Such facts do not appear to warrant any general contrast between cross-fertilization and self-fertilization, but only between narrow breeding and line breeding, and of these the line breed- ing appears to be superior because it constitutes an approxima- tion to vegetative propagation and avoids the need of nuclear readjustments with inadequate diversity of descent. The union of two nuclei which are the autogamous progeny of the same individual organism, can hardly require any new adjustments to be made. The formalities of sexual reproduction are ob- served, but diversity of descent, which gives physiological value and evolutionary significance to the process, has been eliminated. Self-fertility and parthenogenesis, like vegetative propagation, have value only as means of avoiding, for a time, the normal results of restriction of descent, not because they represent normal evolutionary methods of organic succession. DIVERSITY REACTIONS IN RESTRICTED DESCENT. Efforts toward the selective improvement of domesticated plants and animals have been accompanied everywhere by the narrowing of the lines of descent, and often by close inbreed- ing. How far this abnormal condition is responsible for the results of experiments with domesticated species, and how far these results are of general evolutionary significance, remains to be considered. Most of our important food-plants were domesticated long before the period covered by human history or tradition, so that the general claim of selective improve- ment through thousands of years could not be denied, and has 'Shamel, A. D., 1906. The Effect of Inbreeding in Plants. Yearbook of U. S. Department Agriculture for 1905, p. 3S6. 386 COOK continued to be accepted as a sufficient cause of the extensive modifications which have taken place. The question has been debated at length on theoretical grounds, but without decisive results, since it appeared to lie outside the range of experimental determination, owing to the vast periods of time which have figured in the calculation. Fortunately, all plant cultures are not the same in method or in history, and the so-called Arabian coffee furnishes an instructive contrast with other domesticated species. Coffee has prob- ably not been in cultivation much more than a thousand years, and has existed but a few centuries, or often only a few decades, in its present centers of production. It is not an annual, but a shrub, or small tree, the selective improvement of which would require more years than planters generally expect to give to the business. Plantations are generally large, and experiments with individual trees are difficult and time-consuming, so that it is only within recent years that the securing of improved varie- ties of coffee has received serious attention. The evolutionary factors of selection and of long periods of local influences of soils and climates are thus alike absent, and yet there is no lack of coffee varieties with abundant diversity in form, habit and color. Their general similarity consists only in being inferior in fertility to the parent type. So much has been written upon the improvement of plants by domestication and selection that this inferiority of coffee varie- ties may seem exceptional, but the apparent anomaly disappears if we reflect that fruit trees and other horticultural plants sup- posed to have been greatly improved in domestication are not grown for the seeds, and hence complete fertility in the sexually reproductive sense has been a minor consideration or even a positive disadvantage ; indeed, with many plants it has been one of the direct objects of selection to reduce the number of seeds or to eliminate them completely. More or less seedless abnormalities are valuable, for example, among the grapes, plums, and oranges. If coffee were cultivated as an edible fruit the new sorts would be of use, since thicker pulp and smaller seeds are frequent characteristics of the berries ; indeed, a coffee which did not produce any normally developed seeds ASPECTS OF KINETIC EVOLUTION 387 was found in 1903 in Costa Rica. As ornamentals, some variations offer new colors and greater abundance of flowers, and the foliage and habit of the trees sometimes deviate strik- ingly from the normal or parent form. Unfortunately, the planters would find an advantage only in the direction of increas- ing the number, size, or weight of the seeds themselves, and they accordingly pronounce the new varieties worthless. Similar abrupt variations of many cultivated plants and animals were studied and described by Darwin as "sports," but it was also known to him that such variations are relatively infertile and do not persist in the presence of the normal or less closely inbred types, so that it has remained for Professor De Vries to base upon such variations a general theory of evolution. The variations, or sports, chiefly studied by Professor De Vries are those of an evening primrose native in North America and escaped from cultivation in Holland, and thus accidentally seg- regated from the wild stock of its species. It belongs, like the coffee, to a family in which there are specialized provisions to assist cross-fertilization, so that the early manifestation of ihe effects of inbreeding might be expected. The variations of (Enothera described by Professor De Vries seem to be closely parallel to those of coffee ; most of them are conspicuously deficient in reproductive fertility, and some are quite sterile. This relative or complete sterility of sports, or variations secured by inbreeding, warns us that evolutionary inferences founded on this class of facts must be carefully revised, since it is obvious that organisms notably deficient in the power of reproduction can not be expected to have played a large role in the process of organic evolution. Nature, like the coffee-plantevs, requires seeds ; reproductive efficiency is the first requisite of survival. A general evolutionary significance of the phenomena of muta- tions becomes apparent when the facts are interpreted from the standpoint of normal heterism, that is, as reactions from the abnormal uniformity which is the first result of restricted descent. The diversity of mutations is greater than the diver- sity of normal heterism, but this is in entire accord with what we know of other physiological reactions of organisms. Muta- 388 COOK tions are at once degenerative and reconstructive, just as the high temperature which attends many diseases of the human organ- ism is at once an evidence of illness and an indication of con- structive systemic reaction. Indiscriminate crossing of muta- tive varieties tends to restore the wild type of the species. Mongrel dogs are wolfish ; mongrel pigeons, even of white ancestry, are blue ; mongrel roosters become red in approxi- mating the primitive game breeds ; mongrel flowers are single and small. Stronger evidence could scarcely be demanded for proving that the interbreeding of the members of a species is a measure of organic stability, not a stationary or uniform stability, but a stability of coherent symbasic motion. EXAGGERATED HETERISM OF CLONIC HYBRIDS. Further evidence that mutations are reactions from abnormally restricted descent may be drawn from the results of sexual re- production among clonic varieties. The sexual offspring of plants which have been subjected to considerable periods of vegetative propagation always show a very large amount of in- dividual diversity. This has caused them to be reckoned as hybrids, though in reality they represent a very distinct type of evolutionary phenomena. Each clonic variety is, after all, only an individual member of its species, and as such varieties have not been selected or bred to uniformity, in the sense of coming true to seed, they and their offspring might be expected to retain the original amount of heterism or normal individual diversity of the wild type of the species. As a matter of fact the sexual offspring of clones have an individual diversity of the order of mutations. The only difference appears to be that all the individuals may be mutants, instead of the relatively small percentages usually appearing in species which have been subjected to courses of selective inbreeding for the elimination of heterism. DIVERSITY RELATIONS BETWEEN SUBSPECIES WITH RESTRICTED DESCENT. As long as the diversity of the members of species appears either as the merely accidental or arbitrary result of environ- ASPECTS OF KINETIC EVOLUTION 389 mental influence or of mechanisms of heredity, both the theory and practice of evolution remain mysterious and contradictory. It is only after the physiological value of diversity in the con- stitution of species has been recognized that we begin to gain a definite appreciation of the practical bearings of evolutionary facts. With nature wrongly interpreted, the results of domesti- cation and breeding were likewise obscured and distorted. As long as our reckoning was based on the false ideal of unifor- mity and stability of species, it was not possible to gain an orderly concept of even the simplest of evolutionary relations, or to escape from the confusion and contraditions which have left even the most concrete investigators in hopeless disaccord. Among breeders of plants there exists the greatest possible diversity of opinion regarding the value of hybridizing as a means of securing new organic forms of superior agricultural utility. Some breeders have secured very valuable hybrids, while others have found hybrids of no use at all as a means of increasing the desirable characters of the species which they were seeking to ameliorate. To explain and reconcile this apparent contradiction is not only a matter of scientific interest in its bearing upon the general subject of evolution ; it is also of much practical importance to be able to distinguish between the different kinds and combinations of subspecific groups and to avoid a waste of efforts upon methods and materials which do not promise useful results. The time has not yet come for the establishment of absolute standards and criteria, if indeed such a time is ever to come. There are unforseen accidents, not only in the best regulated families, but in nature as well. It is the rarely unusual cir- cumstance, the exception to all known rules, which may have great interest and potential value. The sterility of mules is one of the most invariable of the phenomena of hybridization, and yet fertile mules are not altogether unknown, nor is it certain that such an animal might not be a means of securing new and desirable variations of our equine stocks. Hybrids between the different species of bovine animals are generally fertile and readily made, but the establishment of a breed combining the blood of the buffalo and the domestic cow has proved difficult. 390 cook For the practical breeder, as for the scientific investigator, nothing should be taken for granted until verified by actual ex- periment, but it is, nevertheless, useful to have, if possible, a system of interpretation by which results once attained can be understood, and proper discrimination made between the rela- tive prosoects of alternative fields of investigation. Selections, mutations, crosses and hybrids, have entirely different impor- tance in different groups, depending upon the nature of the characters which it is desired to secure, and upon the adapta- bility of the species to different methods of propagation. In the amelioration of coffee, for example, mutations promise little be- cause of their smaller production of seeds, but if the flowers or pulp of the berries were the valuable part, mutations would be as valuable as among other horticultural species. Selection and hybridization have been thought of as two alter- native methods by which evolution might be brought about, and the debate has continued as to which is the better. The question could never be answered in this form, for the assumption on which it is asked is a false one. The normal species, the unit of evolution, is neither stationary nor uniform. It not only makes a slow and gradual advance, as a whole, but it manifests all the time a vast diversity among the different individuals. Some of this diversity is induced by the environment, but much of it is quite spontaneous and continues to appear even in a uniform environment. The value of selection does not lie in any power to cause these inherent differences ; it can only preserve them and pre- vent, as it were, the swinging back of the pendulum of normal diversity. The alert breeder seeks to catch it at its highest and to hold it steadily there. It cannot be held forever, as is now generally recognized. Sooner or later the selected type deterio- rates, and shows itself inferior to some more recent selection which has lost less of the normal vigor of the species. To hybridize selected varieties may serve merely to release the pendulum and allow it to swing back along the curve of normal diversity. The vast majority of the progeny are likely to be inferior to the parents in the special qualities which have made them valuable. Some of them may approach the standard, ASPECTS OF KINETIC EVOLUTION 39I but they seldom or never surpass it. The breeder concludes that hybridizing is a mistake and finds that much more can be accomplished by selection. This conclusion is quite correct if he is dealing only with long-domesticated strains of plants and animals, and if he wishes to obtain from them the greater ac- centuation of some character already specialized by selection. If the varieties are not too unlike, or too long selected, the result of crossing will be to restore the more normal but less desirable diversity. If the varieties crossed are somewhat more remote, the diversities may balance each other into a somewhat uniform intermediate average. Still longer selection may establish the specialized characters as definitely alternative, in the Mendelian sense, so that they do not combine again into a single hereditary pattern, but separate regularly into the two original components, as in the pea hybrids studied by Mendel, and the many other instances discovered by more recent investigators. In none of these three cases or types of hybrids is there any reason to expect an increase of characters beyond the range of accentuation to be reached by selection ; they all involve, instead,' a lessening of the amplitude of diversity obtainable through selection. If the selective specialization of characters of a va- riety were a true step in the evolution of the species, these kinds of hybrids could be called reversions or retrogressions, since they appear to go backward and undo the results of selection. To call them reversions is very misleading, however, from the evolutionary standpoint, since the closely selected type, however useful, represents only a temporary and abnormal phenomenon, a holding of the pendulum of variation to one side, instead of permitting it to describe its normal vibrations, or to change its general position and point of support. The simple analogy of the pendulum proves entirely in- adequate as a means of illustrating the normal conditions and requirements of true evolutionary advances of specific groups, for we are not dealing then with vibrations of single characters, but with a complicated network, a veritable fabric of descent and of character-combinations. The pendulum analogy is ap- propriate only for the single lines or narrow strands of descent which selection separates from the web of the species, and Proc. Wash. Acad. Sci., February, 1907. 392 COOK holds for a time at a point of high expression a character which averages much lower in the species at large. MUTATIVE VARIATION OF SELECTED VARIETIES. The only way in which the accentuation of such a narrowly selected character can be still further increased, beyond the range of normal variation of the species, is by abnormal varia- tion ; that is, by mutation. The narrow selection may be said to induce the mutations because it weakens and unbalances the hereditary tendencies of the variety, but the mutations are by no means limited to the character or quality for which the variety has been selected ; they are likely to take any or all directions. Some of them are generally found to carry the breeder along the lines he desires to follow. Are hybrids between selected varieties of the same plant or animal of no practical breeding utility? Yes, if it is desired to preserve or strengthen the vitality of the organism or to secure in- termediate characters, or new combinations of characters already existing. The general answer must be negative, if the purpose is to obtain new characters, or higher degrees for accentuation of characters already specialized by selection. Instead of securing a larger range of diversity, the contrary results are much more likely to be reached. It may even happen, if the varieties have been subjected to narrow selection, that the hybrid offspring, instead of being more variable than their parents, will actually be more uniform, the hybridization bringing them back, as it were, to the hereditary road from which they were beginning to wander towards mutative degeneration. The mutations are as abnormal, of course, in the strictly evo- lutionary sense, as the narrow descent which induces them, but for agricultural purposes they may be very valuable, and often the abrupt change of form seems to lend them a remarkable vegeta- tive vigor which greatly increases their productive capacity. This is notably the case among plants, and especially among those cultivated for their vegetative parts instead of for their seeds.1 'Cook, O. F., 1904. The Vegetative Vigor of Hybrids and Mutations. Proc. Biological Society of Washington, 17 : 83. ASPECTS OF KINETIC EVOLUTION 393 The facility with which many plants can be propagated from cuttings or by grafting often permits sterile mutations and crosses to be preserved and utilized for long periods of time. Among animals, on the other hand, mutations are of relatively small value. The higher organization of animals renders them liable to earlier and more serious deterioration from inbreeding, though there is great difference in the susceptibility of different kinds of animals. BEHAVIOR OF DISCRIMINATE MUTATIONS. When mutations are crossed with other members of their own immediate group of related individuals they are generally pre- potent. They do not tend to average away and disappear, but are repeated, or even accentuated, in a considerable proportion of each successive generation, and sometimes in all of them. Plant mutations which can be propagated by self-fertilization are often constant from the first, and have been thought by some to represent the formation of genuine new species. When mutations are bred outside of their own group, and especially when they are crossed with the wild type of the species or with the variety which has not been long or closely selected, they are not prepotent, but recessive. The new muta- tive characters appear weaker than the others and may fade out and disappear entirely. The same result may be reached by indiscriminate interbreeding among the representative of two or more mutations or selective varieties. The ancestral characters of the wild type of the species reassert themselves, and may even reappear in crosses between varieties from which they have long been lost. All these and other similar phenomena can be understood, or at least brought into rational relations, if we keep in mind the fact that crosses between the narrowly selected varieties or mutations of the same species tend to restore the original and normal conditions of free interbreeding. They tend, in other words, to repair and reconstruct the normal fabric of symbasic descent, and to reduce the strains and deteriorations caused by too close segregation, too little diversity, and too much inbreeding. Instead of being monstrous or unnatural, these crosses are 394 COOK more normal, more vigorous, and more fertile, than their parents. Why, then, are they called hybrids? Because we have been led astray by the theory of normally uniform and stationary species, in which it was made to appear that anything which interfered with identity of form and structure was essentially unnatural, like a cross between members of species which do not normally breed together, and which produce, when so bred, abnormal progeny. There are many groups in nature which are reckoned as species, but which are no farther apart than some of the varieties of cultivated plants, and which can breed together without difficulty or abnormality. For systematic purposes it is desirable to recognize each separate natural group of organisms as a species, and this can also be justified from evolutionary standpoints, for segregated groups are able to make evolutionary progress on distinct lines, and eventually to become different from other groups of common origin. It often happens, however, that evolutionary progress is not consistent in the vegetative and reproductive parts of the organ- isms. Species which appear very distinct externally may, when brought together, breed freely and normally, while others whose bodily differences are difficult to detect may refuse to mingle or may produce only sterile or otherwise abnormal hybrids. While it is thus difficult or, it may be, impossible, to draw an absolute line of definition, or to restore the old distinction be- tween hybrids and crosses, this does not justify us in ignoring the very wide and very practical differences between the ex- treme conditions of this series of phenomena. ANALOGIES OF HYBRIDS AND MUTATIONS. The phenomena which have the nearest and most genuine relations with hybrids are not crosses, but mutations. Hybrids and mutations can both be described in the same words, as aberrations from normal heredity. Both are due to the same cause, inadequate fertilization, which unbalances the organic equilibrium and gives rise to abrupt variation, usually in many directions at once. Mutations and hybrids show also a general deficiency of fertility. This is carried, very often, to the ex- treme of complete sterility, though there may be present at the ASPECTS OF KINETIC EVOLUTION 395 same time unusual vegetative vigor, analogous, in all probability, to the stimulation of energy of growth which appears in normal crosses and in prepotent new variations. Though no experi- ments are known to have been made with the idea of such a test directly in mind, the indications are that results of mutation and hybridization might prove in the same species almost identical, for many so-called false hybrids do not appear to be the results of a genuine and effective interbreeding, but seem rather to involve an approach to the phenomenon of artificial partheno- genesis, somewhat similar to the parthenogenetic development through chemical and mechanical stimuli, described by Loeb and others. The two nuclei of the supposed parents of the false hybrid do not appear to have united and combined the parental qualities, since the progeny shows no definite indication of the traits of one of the supposed parents, either in the first or in subsequent generations. The facts discovered by Guyer in sterile hybrid pigeons, that the parental chromatin elements remain separate and do not undergo a normal mitapsis, illus- trates the possibility of false hybrids, especially in plants and in lower types of animals where parthenogenesis can take place. Such an abnormal and inadequate method of fertilization would explain extensive variations of the progeny, which well deserve to be called false hybrids. Nor is it unlikely that the same explanation may be found to apply to variable hybrids, even when they share the characters of the parents. The indications are that in different cases there are all possible gradations in the extent and efficiency of the combination of the parental ele- ments, from that which affords mere stimulation to that which gives a fully intermediate result. It does not follow, however, that the combination is normal or complete when the first generation is intermediate. The first generation may be intermediate under two nearly opposite con- ditions, as already noted. Crosses are intermediate when the parental elements are thoroughly congruous. Their combina- tion merely restores a normal condition of symbasis, that is, provides a normal amount of diversity of descent. The first generation of hybrids is also intermediate when the parental elements are very diverse and antagonistic. Hybrids which 396 COOK appear quite uniformly intermediate in the first generation may- prove, nevertheless, to be completely sterile, as in the mule, whereas intermediate crosses between narrow varieties are always completely fertile, more so, it may be, than their more inbred parents. No distinction is to be drawn between crosses and hybrids which are uniformly intermediate and at the same time fertile, but there is a wide range of phenomena between an inter- mediate, fertile cross between narrow varieties and an inter- mediate sterile hybrid between diverse species. Next to the hybrids which are intermediate, but sterile, are those which are intermediate and fertile, but show diversity and partial sterility in the second generation, proving that the parental elements did not combine in a manner to afford a stable equilibrium of hered- ity. In another stage of hybridity, with less diversity of parents, the first generation is variable, which may be taken to mean that the parental elements are sufficiently similar to influence each other, instead of exerting a uniform degree of repulsion. Nevertheless, they do not combine readily, but form uncertain and extremely varied combinations. The purpose of this enumeration is to show that with hybrids, as with crosses, there is a series of phenomena which can be described and interpreted in terms of diversity, using as a stand- ard the normal diversity of the individuals of species in nature. In this way it is possible to avoid the ambiguities which have attended the use of the false and artificial standard of uniformity. From normal diversity there may be departures on either side, on the one to abnormal uniformity, on the other to abnormal diversity, and both of these can be reached, as we have seen, in several ways. Uniformity appears : 1. In closely selected varieties (stens). 2. In varieties or individuals propagated from cuttings or by other asexual methods (clones). 3. In the progeny of inbred saltatory variations (mutations). 4. In crosses between moderately inbred stenic varieties. 5. In first generation hybrids between species so remote as to combine with difficulty. Likewise diversity greater than the normal may appear : 1. Among mutations from narrowly inbred varieties. ASPECTS OF KINETIC EVOLUTION 2>9l 2. Among crosses between individual clonic types, long sub- jected to vegetative propagation. 3. In a species or variety which has been placed in new and unwonted conditions (neotopic mutations). 4. Among crosses between narrowly inbred varieties (Mende- lian hybrids). 5. Among hybrids between species not too remote to combine at all, but not sufficiently related to combine in a regular and uniform manner. THE NATURE OF STERILE HYBRIDS. A further distinction of fundamental significance remains to be added to the preceding, before the full range of the phenom- ena of interbreeding can be made apparent. The general im- pression has been that the development of a new individual represented the result of a combination of the two parental sex- cells, but this is only partially true, especially among the higher plants and animals. The fusion of the parental sex-cells is carried through only two of the three stages of conjugation. Fertilization unites the outer, unspecialized protoplasms (plas- mapsis) and also the nuclei (karyapsis), but the chromatin, the most highly specialized cell-substance, the citadel, as it were, of the life of the cells, remains distinct until after the new individual has developed, so that the body is not composed of simple, post-conjugational cells, but of double cells in a condi- tion of prolonged conjugation. The fusion of the chromatin granules, or ultimate sex-ele- ments (mitapsis), may not take place until the new individual is mature and about to form new sex-cells of its own. The other cells of the body never reach mitapsis. The sterility of hybrids arises, it is now believed, from the inability of the sex-elements to pass this third and final stage of conjugation. It was always mysterious that hybrid combinations which could be made for one generation could not continue for a second or a third generation. This new appreciation of the nature of the process of conjugation makes it apparent, however, that hybrids are sterile because the parental elements do not make even one complete conjugation. There is thus a definite difference 398 COOK between a sterile hybrid and a fertile combination, one which might have restricted the use of the term hybrid to the former. Sterile hybrids, like false hybrids, are scarcely to be reckoned as forms of conjugation. They are rather to be looked upon as more nearly allied to parthenogenesis, a development through stimulation merely, but without the possibility of forming new relations of heredity or of making new combinations of charac- ters. Sometimes there is not even enough cooperation between the mismated partners of the cell-units to carry the organism through even the normal cycle of individual existence. Hybrids often refuse to grow up, or they may die suddenly and without apparent external cause. The building up of each cellular organism involves a contin- ued cooperation between the parental sex-elements, which may be thought of as persisting in all the cells of which the body is composed. Whenever this cooperation breaks down, or proves inadequate, the further development of the conjugate organism becomes impossible. PAPERS RELATING TO KINETIC EVOLUTION. i 895. An Arrangement of the Geophilidae, a Family of Chilopoda. Proc. U. S. Nat. Museum, 18: 63. 1896. Note on the Classification of Diplopoda. American Naturalist, 30: 681. i8gg. Four Categories of Species. American Naturalist, 33 : 287. 1901. Duoporus, a New Diplopod from Mexico. Proc. Ent. Soc. of Washing- ton, 4 : 402. 1901. A Kinetic Theory of Evolution. Science, N. S., 13 : 969. 1902. Evolutionary Inferences from the Diplopoda. Proc. Entomological Soc. of Washington, 5 : 14. 1902. The Earwig's Forceps and the Phylogeny of Insects. Proc. Ent. Soc. of Washington, 5 : 84. 1902. Kinetic Evolution in Man. Science, N. S., 15 : 927. 1902. A Deciduous Tropical Tree. Plant World, 5 : 171. 1903. Stages of Vital Motion. Popular Science Monthly, 63 : 14. 1903. Evolution, Cytology and Mendel's Laws. Pop. Sci. Mon., 63 : 219. 1904. Evolution not the Origin of Species. Pop. Sci. Mon., 64: 445. 1904. Professor Metcalf's Evolution Catechism. Science, N. S., 19: 312. 1904. Natural Selection in Kinetic Evolution. Science, N. S., 19: 594. 1904. The Vegetative Vigor of Hybrids and Mutations. Proc. Biological Soc. of Washington, 17 : 83. 1904. Evolution and Physics. Science, N. S., 20: 87. 1904. The Biological Evolution of Language. The Monist, 14: 4S1. 1904. Evolution of Weevil-Resistance in Cotton. Science, N. S., 20: 666. 1905. The Social Organization and Breeding Habits of the Cotton-Protecting Kelep of Guatemala. Bull. 10, Technical Series, Bureau of Entomology, U. S. Department of Agriculture. 1905. Evolution of Cellular Structures. Bull. 81, Bureau of Plant Industry, U. S. Department of Agriculture. (W. T. Swingle, joint author.) 1905. The Evolutionary Significance of Species. Smithsonian Report for 1904. P- 397- igo6. Weevil-Resisting Adaptations of the Cotton Plant. Bull. 8S, Bureau of Plant Industry, U. S. Department of Agriculture. 1906. The Vital Fabric of Descent. Proc. Washington Academy of Sciences, 7: 301. 1906. Factors of Species-Formation. Science, N. S., 23: 506. 1906. The Nature of Evolution. Science, N. S., 24: 303. 399 INDEX. acclimatization 263 accommodation differences 202, 235, 236 Achillea 372 Aconitum 372 acquired characters 222, 319 Actcza 371 adaptation 211, 276, 283 defined 199, 278 adaptations, symbasie 220 adaptive fitness 222 versatility 200 adjustment of locomotion 207 characters 205 African diplopods 269, 312 agamic cell-structures 368 Agave, heterism of 247 agents of evolution 314 agricultural instincts 251 agriculture, primitive 251 albinism 337 alternation of generations 240, 366 alternative adjustment characters 205 heredity 345 anthropoids 217 antidromous plants 371 apaulogamic cell-structures 368 apogamic bulblets 383 Arctic plants, apogamous 384 plover, migrations of 211 Aristotle's categories 282 arropic species 369 artism 235, 250 astronomy and biology 356 autogamy 377, 384 barley, linic species 377 bees, sex-determination of 347 biology, compared to astronomy 356 human 218 bionomy of species 364 bovine hybrids 389 branch dimorphism 242 bud mutations 351 variations 354 Burbank on Prunus 352 cacao, dimorphic branches of 242 Castillo., dimorphic branches of 242 categories of causation 282 Cattell, quoted 282 cell differentiation 239, 329 cellular organization 367 structures, three types 238 Ceratodon 376 cerebral development 217 change of seed 262 character-unit assumption 339, 342, 353 chromomeres 342 chromosome purity 337 chromosomes 336 positional relations of 353 temporary 338 chromatin of hybrids 348 chrysomelid beetles, dichromatism of 376 civilizations suicidal 217 clones, definition of 378 clonic conditions 383 hybrids 388 propagation 380 species 378 varieties, limitations of 382 Cockayne, reference to 259 coffee, accommodations 210 amelioration of 390 dimorphic branches of 242 mutations 253, 271, 275, 325, 386 colors of desert animals 213 combined forms of diversity 379 conjugate cell-structures 368 heredity 344 organisms 330, 349 periods 365 conjugation, evolution of 330 nature of 343 conscious selection 278 conspicuous colors in forests 214 constant of variation 315 constitution of species 356 continuity of evolution 309 corn, Indian 264 correlation of variations 221 cotton acclimatization 201, 263 dimorphic branches 242 variations 201 Coues, on uniformity 291 cross-fertilizing adaptations 220 crystallization compared to heredity 332 Darwin, G. H., on natural selection 292 Darwin, Charles, on variation 229 on substitution 281 Darwinia, N. formulae 284 Darwinism 223, 230, 320 degeneration 255, 273 Delphinium 371 dendritic conception of descent 197 descent differences 235 desert colors 213 plants 213 deterioration of varieties 382 under inbreeding 381 determinant theories 300, 316 defined 306 DeVries, elementary species 378 on mutations 314, 324 on selection 322 on uniform species 362 theory of 387 dichromatism 375 dimorphic branches 242 diplopods, African 269, 312 Discaria experiment 258 discontinuous motion 309 variations 300 400 ASPECTS OF KINETIC EVOLUTION 401 discriminate mutations 393 disjunction 337 diversity, conditions of 396 of hybrids 388 reactions 385 domesticated species 359 domestication of food plants 385 dominant characters 337 double-celled organisms 344 Draba 378, 383 dynamic causes 304 educational danger 367 elementary species 378 elimination 281 elk, antlers burdensome 217 Engler, on mountain plants 267 environment, definitions 223 environmental fortuity 215 influence 335 reactions 213 ethics of race 335 Eucalyptus, metamorphosis 241 evening-primrose mutations 387 evolution a process 289 by restricted descent 378 defined 277 theories compared 307 evolutionary species 210 exaggerated heterism 388 explanations of evolution 288 expression problem 294 false hybrids 395 fasciation 352 Ficus 220 fig insect 219 fish with protective color 214 fitness by correlation 221 origin of 222 problem 198 forces of evolution 328 formulae of evolution 285 fortuity 215 of environment 218 frog with protective color 214 galls, heredity of 352 genetic variations 236 germinal incompatibility 348 selection 301 Gomphodesmidae 312 graft-hybridism 352 growth defined 330 stages 235, 237 Gulick isolation theory 314, 318, 377 Guyer on hybrids 348 Hawaiian snails 377 Helix 377 heredity, alternative or polar 345 and crystallization 332 and environment 333 and heterism 353 concept 327 in cell-specialization 329 hermaphroditism 370 heterism 244, 279, 327 and heredity ,353 and sex 374 heterism defined 235 functions of 248, 346 of clonic hybrids 388 specialization of 247, 369 hetercecism 241 heterogamy 384 Hieracium, linic species 378 Houslonia 372 human descent 355 evolution 363 Huxley, quoted 286 Hyatt's evolutionary forces 328 hybrids, diversity of 388 of clones 388 like mutations 394 sterile 397 various kinds 395 hybridization, limits of 394 versus selection 390 inbreeding, effects of 382 inconspicuous colors 213 infusoria, nuclei of 354 integral theory 197 intellect over-developed 217 interbreeding as evolutionary factor 323 intermittent evolution 309 intraspecific differences 226, 235 figure of descent 197 isolation defined 278 theory 314 Jordan, on selection 260 Juniperus, metamorphosis 241 karyapsis 397 Kelvin, opinion of 343 kinetic figure of evolution 323 theory defined 295, 302, 306 Knowlton, on bird migration 211 Lamarckian adaptations 230 L,amarekian theory 314, 333 Lankester, on heredity 333 on selection 323 on useless differences 314 laws and processes 289 leopard, black 375 Liberian fish 214 limitations of clonic propagation 380 line-bred organisms 377 lines, definition of 377 linic conditions 383 species 377 living matter specific 358 lizard with protective habits 214 Lydekker, on sheep 260 Ly thrum, heterism of 346, 372 maize varieties, 377, 384 mathematical heredity 339 Maupas, on nuclei of infusoria 354 mechanical theories 319 Mendelisni and sex 348 Mendelian heredity 336 Merocheta 312 metamorphosis 240 metagenesis 240 Metcalf, on plasticitity 204, 206 mice experiments 337 402 COOK millipeds 270, 312 mitapsis 338, 397 _ _ Mivart. on abrupt variations 231 on natural selection 283 modes of evolutionary motion 286 mongrel reversions 388 monkeys 217 mules sometimes fertile 385 mutation theory 308, 313 mutations 274 degenerative 309, 310 discriminate 393 diversity of 387 of tomato 265 like hybrids 394 parallel 221 post-reproductive 352 prepotency of 393 teratic neisms 236 versus species 310 mutative variation 392 myxomycetes, accommodation in 208 chromatin of 354 Naegeli's theory 256, 300, 316, 378 natural selection 227, 232 selection negative 321 neism 236, 269 neotopism 236, 261 network motion 323 new characters prepotent 319 place effects 236 variations 269 nuclear deterioration 354 (Edogonium 239 olfactory cones of millipeds 312 organic elasticity 200 utility 215 overlapping of generations 367 Oxalis 372 Oxydesmidse 270 paint-root 257 pangenesis 316, 329 panmixia 256 paragamic cell-structures 368 parasitic fungi 241 tendencies 217 parthenogenesis 398 particularization 289 pendulum analogy 390 pheasants, plumage over-developed 217 philosophical systems 296 physiological species 210 physiology of cells 356 of evolution 304 of species 362 pigeon experiment 337 plasmapsis 397 plasticity in evolution 203 Poa 376 polar heredity 345, 348 politism 242 porric species 376 porrism 2^6, 266 Portulaca 376 positional relations of chromosomes 353 post-conjugate heredity 344 predetermination hypothesis 327 prefiguration hypothesis 327 premature socialization 367 prepotency 231, 271 of variations 319 preservation of characters 319 protective colors 213 proterandry in coffee 275 proterogyny in coffee 275 Prowazek, on chromatin 354 Prunus, graft-hybrid 352 Ptolemaic astronomers 293 pure science 360 purity of germ-cells 336 quail, subspecies of 267, 377 race evolution 335 rapidity of evolutionary motion 308 recessive characters 337 reproduction defined 330 restricted descent 376, 385, 388 descent, theories of 378 reticular descent 197 reversions 388, 391 root-crops, tropical 381 ropic species 370 Russian thistle 261 rust fungi 241 rye, a coherent species 384 saltatory evolution 299, 305, 309 screech-owls, supersexes of 375 secondary sexual characters 346 sections of species 364 seedless plants 273, 378 species unknown 381 segregation 278 selection defined 278 function of 389 inadequate 198 induces mutation 392 in mutation theory 310 preserves variations 390 versus hybridization 390 selective perfection of adaptations 212 restriction of descent 379 self-fertilization 377 semisexes, definition of 372 semisexual species 372 sex and Mendelism 348 -determination 347, 351 -differentiation 350, 355 sexual characters 373 selection 374 species 372 sexuality of conjugate organisms 349 of plants 350 Shamel, on tobacco 385 sheep in tropics 260 social organization 217, 242 of cells 238 socialization, premature 367 speciation 205, 276, 279 defined 278 theories of 279 species and subspecies 268 constitution of 356, 369, 376 in motion 294, 306 meaning of 359, 362 physiology 362 specific organization 327 ASPECTS OF KINETIC EVOLUTION 403 spiny plants 258 Spirogyra 331 spring-blossoming plants 383 Standfuss, experiments of 253 static theories defined 233, 298, 305 stenic species 377 stens, definition of 377 sterile hybrids 348, 397 structure of species 357 subsexes, definition of 371 subsexual species 371 subspecifie diversity 379 substitution 281 supersexes, definition of 375 supersexual species 375 Swingle, on positional heredity 353 symbasic adaptations 220 evolution 302 species 311, 376 symbasis, function of 323 symbasis defined 277, 317 synthetic theory 197 tables comparing theories 307 taxonomy inadequate 361 temperature range of plants and animals 211 teratic neisms 236 teratism 236, 272 termite organization 243 termites, heredity of 345 tobacco experiments 385 tomato mutations 265 topism 236, 257 unconscious selection 278 uniformity, conditions of 396 uniformity by autogamy 385 unisexual coffee mutations 275 use and disuse phenomena 254 utility, environmental and organic 215 of new characters 318 of sex characters 373 variation, discovery of 229 variations under domestication 360 vegetative propagation 366, 381 variations 351 vigor 380 Verbascum 249, 371 versatility of organisms 200 Viola 371, 383 Virginia partridge 267 vital tension 303, 355 network 355 Wallace, on natural selection 292 Washington palm 212 wealth and deterioration 218 Weismann on heredity 256, 300, 316 wheat, linic species 377 White on tomatoes 265 PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 405-406. February 13, 1907. AGE OF THE PRE-VOLCANIC AURIFEROUS GRAVELS IN CALIFORNIA. By J. S. Diller. GENERAL STATEMENT. The age of the auriferous gravels of the Sierra Nevada in California is generally given as late Miocene or Pliocene and is based chiefly on fossil plants and a few animal forms. The auriferous gravel period in all probability was a long one and no considerable part of its flora has yet been connected directly with its contemporaneous marine fauna of the same region. On physiographic and stratigraphic grounds and the general relations of the Sierra Nevada to sedimentation, it has long been supposed by some geologists that the oldest auriferous gravels, the deep gravels of Lindgren, are probably Eocene, but the evidence assigned is problematic rather then positive. EOCENE FLORA OF SOUTHWEST OREGON While studying the Eocene deposits of the Roseburg, Coos Bay, and Riddles quadrangles in Oregon, fossil leaves were found in the same strata with marine shells, thus affording an opportunity definitely to connect the land flora with its contem- poraneous marine fauna. The following list of ten species embraces the Eocene plants identified by Dr. F. H. Knovvlton with more or less certainty from a number of localities within the area noted above : Magnolia lanceolata Lesq. Magnolia californica ? Lesq. Laurus californica ? Lesq. Sabalites calif ornicus ? Lesq. Aralia whitneyi Lesq. Proc. Wash. Acad. Sci., February, 1906. ( 405 ) 406 DILLER Pofiulus zaddachi Heer. Aralia angustiloba ? Lesq. Juglans califomica P Lesq. Ulmus califomica Lesq. Ficus tilicBfolia ? Al Branner. Among the shells found with or very near the fossil leaves, Dr. Wm. H. Dall has recognized over 20 genera, and remarks : "The fossils are Eocene. They contain a number of inter- esting things, particularly the Orbitolites, which is usually char- acteristic of the Oligocene on the Atlantic coast and is now for the first time recognized from the Pacific coast." The fossil leaves were found near the southeast border of the Eocene where shells are not abundant, but a short distance far- ther northeast they become very abundant locally with such characteristic forms as Venericardia planicosta and Turritella nvasana, and there is no doubt concerning the Eocene age of the strata containing the fossil leaves. Of the 10 species of plants identified seven are somewhat in doubt, but three, Magnolia lanceolata, Aralia zvhitneyi, and Populus zaddachi, are completely satisfactory. They all occur in the auriferous gravels of Independence Hill, on the western slope of the Sierra Nevada, as well as on the summit of the northern end of the range, 7^ miles southwest of Susanville. The last species occurs at many other localities among which may be mentioned the lone formation of Kosk Creek and Little Cow Creek of Shasta County, Cal., and the auriferous gravels of Moonlight, Chalk Bluff, and Volcanic Hill. Eight of the 10 species reported from the Eocene of Oregon, occur, according to Mr. Lindgren, in the "bench gravels" of Independence Hill, in California. It seems probable therefore that not only the " deep gravels " but also the " bench gravels," both of which belong to the pre-volcanic gravels, may be of Eocene age. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 407-448. pls. IX-XX March 4, 1907. AERIAL LOCOMOTION. With a Fe, No. 12, December, pp. 270-274. 1894 Die Flugapparate, Berlin, Sonderabdruck aus Nr. 6 der Zeitschrift fiir Luftechiffahrt und Physik der Atmosphare. Berlin, pp. 3-15. 1895 Les Experiences de M. Lilienthal par M. P. Lauriol. Revue de L'Aero- nautique, 8 Annee, ire Livraison, pp. 1-10. i8g6 Practical Experiments for the Development of Human Flight. The Aeronautical Annual, No. 2, Boston, pp. 7-22. 1897 At Rhinow. The Aeronautical Annual, No. 3, Boston, pp. 92-94. 1897 The Best Shapes for Wings. The Aeronautical Annual, Boston, No. 3, PP- 95-97- 1897 Der Kunstrlug. In : Taschenbuch f. Flugtechniker 2. 1894 Aurl., Berlin (313-321). Hargrave, Lawrence 1889 Flying Machine Memoranda. Journal and Proceedings of the Royal Society of New South Wales, Sydney, vol. XXIII, part 1, pages 70-74. 1890 On a Compressed-air Flying-machine. Journal and Proceedings of the Royal Society of New South Wales, Sydney, vol. XXIV, part 1, pages 52-57- 1892 Flying-Machine Work and the 1/6 I. H. P. Steam Motor Weighing 2>lA lbs. (Reprint). Journal and Proceedings of the Royal Society of New South Wales, vol. XXVI, pages 170-175. 1892 Flying-Machine Work and the 1/6 I. H. P. Steam Motor Weighing 3% lbs. Journal and Proceedings of the Royal Society of New South Wales, Sydney, vol. XXVI, pages 170-175. 1896 On the Cellular Kite. (Reprint.) Journal and Proceedings of the Royal Society of New South Wales, vol. XXX, pages 1-4. 1898 "Aeronautics." (Reprint.) Journal and Proceedings of the Royal Society of New South Wales, vol. XXXII, pages 55-65. 1903 Hargrave's Versuche, 111. aeron. Mitt., Strassburg, 7, (366-370). Herring, A. M. 1896 Dynamic Flight. Aeronautical Annual, Boston, No. 2, pp. 89-101. 1897 Recent Advances Toward a Solution of the Problem of the Century. Aeronautical Annual, Boston, No. 3, pp. 54-74. 1899 Die Regulirung von Flugmaschinen. Zeitschrift fiir Luftschiftahrt und Physik der Atmosphare. Berlin, XVIII, Heft 9, pp. 205-211. 1899 Einige sehr leichte Benzin- und Dampfmotoren. Zeitschrift fiir Luft- schiffahrt und Physik der Atmosphare. Berlin, XIX. Heft 1, pp. 1-4. 44» BELL List of Articles Relating to Aeronautics Published by the Smithsonian Institution. No. Author. Arago, Francis... 789 8oi Glaisher, James... Wenham, F. H. .. Langley, S. P. ... 884 Langley, S. P. ... 938 Lilienthal.Otto... "34 "35 Huffaker, E. C... 1 149 1 197 1248 Bacon, John M ... 1267 1268 Janssen, J 1269 1270 1352 Curtis,Thomas E. Lyle, E. P., Jr.... 1358 1379 Baden-Powell, Maj. B. F. S. 1380 H43 Wright, Wilbur... Pettigrew, Jas. Bell 1494 M95 1496 1597 Baden-Powell, Maj. B. Langley, S. P ,,, 1598 von Lendenfeld, R Title. Aeronautic Voyages performed with a view to the advancement of science. An Account of Balloon Ascensions. On Aerial Locomotion Experiments in Aerodynamics The Internal Work of the Wind Where Published. The Problem of Flying and Prac- tical Experiments in Soaring. Story of Experiments in Mechan- ical Flight On Soaring Flight Letters from the Andr^e Party , Scientific Ballooning Count Von Zeppelin's Dirigible Air Ship , The Progress of Aeronautics Lord Rayleigh on Flight , The Langley Aerodrome (Note pre- pared for the conversazione of the j Amer. Inst, of Elec. Engineers, New York City, April 12, 1901). The Zeppelin Air Ship Santos-Dumont Circling the Eiffel Tower in an Air Ship The Greatest Flying Creature Recent Aeronautical Progress, and Deductions to be drawn therefrom regarding the Future of Aerial Navigation. Some Aeronautical Experiments On the Various Modes of Flight in Relation to Aeronautics Progress with Air Ships Aerial Navigation Graham Bell's Tetrahedral Kites Experiments with the Langley Aero- drome Relation of Wing Surface to Weight. Report, 1904 Report, 1863. Report, 1863. Report, 1889. Cont. to knowl- edge, Vol. 27. Cont. to knowl- edge, Vol. 27. Report, 1893. Report, 1897. Report, 1897. Report, 1897. Report, 1898. Report, 1899. Report, 1900. Report, 1900. Report, 1900. Report, 1900. Report, 1901. Report, 1 901. Report, 1902 Report, 1902 Report, 1867 Report, 1903 Report, 1903 Report, 1903 Report, 1904 Proc. Wash. Acad. Sci.. Vol. VIII Plate IX. I.ilienthal Gliding Machine as reproduced in America for Chanute by Herring. Gliding through the air on Chanute's Multiple-winged Glider. Proc. Wash. Acad. Sci., Vol. VIII. Plate X. Langley's Aerodrome No. 5 in flight, May 6, 1896. From instantaneous photograph by Alexander Graham Bell. Proc. Wash. Acad. Sci., Vol. VIII. Plate XI. * 5? » 3 ft fl* < O 5'c 5-i f r 3- (0 8 t B ?3 =2. ° s> n> 3-3* ^. O J U) ^ n > * 2 rt: Proc. Wash. Acad. Sci., Vol. VIII. PlatejXII. o kLf „ i^^^ i '^i*000* M. A V 1 Si ^1 • i^ii It Proc. Wash. Acad. Sci., Vol. VIII. Plate XlH. n W 2. crq 5 K r» ** Proc. Wash. Acad. Sci., Vol. VIII. Plate XIV. Proc. Wash. Acad. Sci., Vol. VIM Plate XV. The Frost King in the air, flying in a ten-mile breeze, and supporting a man on the flying rope. During the experiment the rope straightened under the pull of the kite, and the man was raised to a height nfM ™- &&£s^^S^SSS^&Sff. brought doWD safely- »«££ to •O c 3-1 ° 2 — 2. O He ° 3 "> Proc. Wash. Acad. Sci., Vol. VIII. Plate XVIII. A Floating Kite, adapted to be towed out of the water. Kite consistsof a bridge, ortruss, of tetrahedral celN with wings of Japanese waterproof piper upon two floats of light framework covered with oilcloth. A stint towing pole extends laterally across the lower part of the wing- piece at the front. Photograph by Douglas McCurdy. Illustration from the National Geographic Society. Proc. Wash. Acad. Sci., Vol. VIII. Plate XIX. 1 The French Military Dirigible, " Patrie," in flight. The latest French airship. " La Patrie," is ,i,v, feet in diameter by 196 feet long, and has a capacity ot 111,195 cubic feet. Driven by a 70-horsepower motor and two propellers, this dirigible has recently made about 30 miles an hour. Its lifting capacity is 2,777 pounds. Illustration from the Scientific American. The New Deutsch Airship, " Ville de Paris," the latest dirigible balloon. The peculiar arrangement of twin, hydrogen-filled cylinders forms a sort of balancing tail. This airship has a length of 60 meters (196.85 feet) and a diameter of 10. S meters (35.43 feet) while its capacity is 3,000 cubic meters (105,943 cubic feet). Its propellers are placed on either side of the body framework, or " nacelle," and at about the center of the latter, which is boat-shaped. The weight which can be carried, outside of the equipment and the fuel sufficient for a ten hours' run, is about 1,100 pounds. A 70-horsepower Panhard motor is used. Illustration from the Scientific A merican. Proc. Wash. Acad. Sci.. Vol. VIII. Plate XX. Count Von Zeppelin's Airship— the largest and fastest thus far constructed — coming out of its shed and performing various evolutions above Lake Constance. {.This airship, which is 38 feet in diameter by 410 feet in length and which lias a capacity of 367,120 cubic feet, held itself ., stationary against a 33'2-mile-an-hour wind in January last, by means ol two 35-horsepower gasoline motors driv- ing four propellers. The airship can lift three tons additional to its own weight, which gives it a radius of 3,0:0 miles at 31 miles an hour. On October 11, 1906, Count Zeppelin maneuvered this dirigible balloon above Lake Geneva, ascending to a height of 2.500 feet and steering the huge cigar-shaped ai'-rostat very nicelv. The airship is mounted on floats, so that it works equally well on the water. During one flight it remained in the air an hour _^ and twenty minutes, although the steering-gear was caught in the skeleton framework and became partly unman- i J ageable. The attempts proved also that the airship was dirigible in spite of its great size, as several complete t .. circles were made while in the air. Illustrations from the Scientific American. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 449-458. Plates XXI-XXIII March 4, 1907. ON A COLLECTION OF FISHES FROM BUENOS AIRES.1 By Carl H. Eigenmann. The present paper is a report on a collection of fishes obtained near Buenos Aires, Argentina, by Prof. W. B. Scott, of Prince- ton University. The collection adds several species to the La Plata fauna. These are marked*. Four of these species are new. The types are in the Museum of Princeton University, and a series of cotypes and duplicates is in the Museum of Indiana University. The fresh-water fish fauna of Buenos Aires is essentially Amazonian and in striking contrast to the fresh-water fauna of North America of corresponding latitude and equally remote from the mouth of the Amazon which lies on the equator. None of the Amazon genera has passed much beyond the borders of the United States. Most of them do not reach beyond Panama. The Paraguay, whose sources are in contact with those of the Tapajos and Madeira, southern tributaries of the Amazon, has provided an easy and open road for the Amazon fauna to the Lower Parana and La Plata. But few Amazon types extend south of Buenos Aires. silurid^:. Luciopimelodus pati Valenciennes. One specimen. Pseudaplatystoma coruscans Agassiz. One specimen. * Contributions from the Zoological Laboratory of Indiana University, No. 80. Proc. Wash. Acad. Sci., March, 1907. 449 450 EIGENMANN Rhamdia quelen Qiioy & Gaimard. One specimen. Pimelodus clarias macrospila Giinther. Two specimens, each with 3 series of large spots. Pimelodus albicans Valenciennes. One specimen. Pimelodus valenciennis Kroyer. Four specimens. Iheringichthys labrosus (Kroyer). Several specimens. Doras granulosus Valenciennes. A single specimen, 470 mm. long. Lateral line 22, the hooks of the lateral plates beginning under the end of the dorsal. LORICARIID^ Plecostomus commersoni Cuvier & Valenciennes. Four specimens. * Plecostomus laplatae Eigenmann, new species. (Plate XXI.) Depth 5 in length; head 3.4 (3.28 in cotype) ; D. 1, 7 (not counting the fulcrum); A. 1, 4 ; scutes 31 -f 1 caudal scute; depth of head 1.75 (1.66) ; width of head 1.2 in its length (1 + ) ; length of snout equaling depth of head (1.5 in head); inter- orbital 2.8 in head (2.66); length of mandibular ramus 3 in interorbital (2 + ) ; barbel more than half length of eye; snout spatulate, rounded ; supraorbital margin not raised ; supraoccip- ital ridge very feeble, temporal plates not carinate ; scutes of sides little keeled, spinulose, 7 between dorsal and adipose, 14 to 16 between anal and caudal ; supraoccipital bordered by a median and two or three lateral scutes. Lower surface of head and belly entirely granulose in the type, partly naked between the base of pectoral and ventral. First dorsal ray about equal to length of head, last ray .66 (.5) length of head ; base of dor- sal equal to its distance from end of second scute beyond tip of adipose spine ; pectoral extending to second sixth of the ventrals ; caudal distinctly emarginate ; caudal peduncle a little more than 3 times as long as deep. COLLECTION OF FISHES FROM BUENOS AIRES 45 1 Color of type : Sides, ventral surface and head profusely spotted, the spots largest on the belly, minute on the head ; lightish streaks along the lateral keels ; dorsal dusky with one or two rows of spots between every two rays ; caudal unspotted, the lower part dusky ; anal dark, unspotted ; ventrals and pec- torals dusky, the former with large spots, the basal two thirds of the latter with very numerous minute spots similar to those of head. Color of cotype : Ventral surface plain ; sides with obscure large spots, the light streaks along the keels much more evi- dent ; head profusely covered with spots much larger than those in the type ; dorsal with a series of large spots on the posterior half of each interradial membrane ; caudal sooty, anal obscurely spotted ; entire upper surfaces of ventrals and pectorals spotted, the spots of the pectoral more numerous and smaller, but not as small as those of the head. Apparently related to Plecostomus carinatus vaillanti and tietensis. Type in Mus. Princeton Univ., a specimen 410 mm. long, from Buenos Aires; coll. Prof. W. B. Scott. Cotype, no. 11351, Mus. Ind. Univ., a specimen 214 mm. long, from same place. Loricaria vetula Cuvier & Valenciennes. (Plate XXII.) One specimen. Loricaria anus Cuvier & Valenciennes. Six specimens. These specimens have the lateral keels separate to the last 3 or 4 scutes ; the dorsal without spots but with the second half of the membrane dark. CHARACID^. Curimatus platanus Giinther. One specimen. Curimatus gilberti Quoy & Gaimard. Two specimens. Prochilodus lineatus (Valenciennes). Six specimens, the largest 430 mm. 45 2 EIGENMANN Leporinus obtusidens (Valenciennes). One specimen. Depth 3.5; head 4.33; interorbital equals snout ; snout conical ; teeth short, truncate ; lateral spots ob- scure, vertical, the caudal spot most prominent; anal concave, the second and third ray reaching much beyond the tip of the last, nearly to caudal. Astyanax rutilus (Jenyns). Five specimens. D. 11 ; A. 28 in one, 30 in the others; scales 6 or 7-37 to 39-5 to 7. * Acestrorhamphus brachycephalus (Cope). One specimen. D. 10; A. 26 ; head 3.75 ; depth 3.33 ; eye 4 in head; scales 1 1-55-9. Acestrorhamphus hepsetus (Cuvier). One specimen. * Acestrorhamphus ferox (Giinther). One specimen. Salminus maxillosus (Cuvier & Valenciennes). Three specimens. In the older ones the dark lateral lines are much more con- spicuous than in the younger. Serrasalmo marginatus Valenciennes. Two specimens. Hoplias malabaricus (Bloch). Two specimens. clupeid^:. Pomolobus ? melanostomus Eigenmann, new species. (Plate XXIII, Fig. 6.) I am not sure of the identification of this species. It differs from the other American relatives of Clufea in having the dorsal inserted behind the ventrals. D. 13 to 16 ; A. 17 to 20 ; head 4.5 to 5 ; depth 3.33 to 3.66 ; ventral serrae strong, beginning near posterior margin of pre- opercle, 26-29. -^ye a ntt^e longer than snout, 3 to 3.5 in head ; mouth oblique, the lower jaw included ; maxillary extending a little beyond front of eye ; gillrakers about two thirds as long as eye ; no teeth on vomer ; alimentary canal short, peritoneum COLLECTION OF FISHES FROM BUENOS AIRES 453 white ; dorsal short, its origin over some part of the last third of the ventrals, a little nearer caudal than tip of snout. Scales caducous, crenulate. A dark band along the entire back, median predorsal line free from pigment ; a faint dusky streak along the upper part of the side to the middle of caudal ; no humeral spot ; upper lip black, tip of snout and lower jaw dusky ; sides of head and body without pigment cells. The reproductive organs indicate that the larger specimens are mature. Type in Mus. Princeton Univ., a specimen 85 mm. long, from Buenos Aires; coll. Prof. W. B. Scott. Cotypes in the collections of Princeton and Indiana Universities (No. 11364, Mus. Ind. Univ.), 14 specimens 58 to 85 mm. long, from same place. STOLEPHORID^). Ilisha flavipinnis (Valenciennes). Two specimens. Stolephorus olidus Gtinther. Seven specimens. Upper margin of silvery band well denned, the lower margin not, the silvery area in the adult covering the entire sides. Anal about 26; depth about 5.5 (4.5 in the types). MUGILID^. Mugil platanus Giinther. Five specimens. These agree with Giinther's description, except that in the three better preserved specimens and the smallest the upper half of the base of the pectoral is black, the rest of the fin uniform. ATHERINID^. Atherinichthys bonariensis Cuvier & Valenciennes. Four specimens. Atherinichthys argentinensis Cuvier & Valenciennes. Origin of spinous dorsal behind anus. A. 1, 15 ; scales 50, 8 between dorsal and anal ; depth 6.5 to base of caudal ; head 4.33 ; scales rounded behind; pectorals equal head less mouth ; lateral band one sixth depth of body. 454 EIGENMANN sci^nid^:. Pachyurus bonariensis Steindachner. Many specimens. cichlid^:. Heros autochthon Giinther. Two specimens. Geophagus australe Eigenmann, new species. (Plate XXIII, Fig. 7-) Closely related to G. duodecimspinosum = balzanii, from the Paraguay. It differs from that species in the more pointed snout, less steep profile, more rapidly descending dorsal slope, longer, more slender caudal peduncle, narrower interorbital, etc. It differs from its next nearest relative, G. gymdogenys, in the scales of the cheek and in the color. Head 3 to 3.16; depth 2 to 2.4; D. xn to xiv, 10 or 11; A. in, 8 ; lateral line 28 to 30 (16 to 18 + 10 to 12) ; 25 to 27 scales along the middle of the side. Subrhomboidal ; dorsal outline unequally arched, the highest point at the origin of the dorsal. In G. balzanii the dorsal profile is much more regularly arched from the tip of snout to end of dorsal ; anterior profile convex in front of dorsal, nearly stra'ght on head ; caudal peduncle rather long and slender, its depth 1 to 1.33 in its length ; interorbital very convex, the bony portion 3.5 in the head (2.5 in balzanii) ; cheeks with 3 series of scales on their upper part, the lower portion naked (about 7 series in balzanii) ; 7 or 8 tubercular gillrakers on lower half of arch ; a single complete series of scales on the subopercle with a few scales forming an imperfect second series below them. Eye 4 to 4.5 in head ; nares half way between tip of snout and eye (distance of nares from tip of snout 1.6 in their distance from eye in balzanii). Ventrals reaching the anal papilla or slightly beyond origin of anal ; pectoral reaching to first anal spine or first anal ray ; soft dorsal and anal high, reaching considerably beyond base of caudal ; caudal lunate or but slightly emarginate, its base much less densely scaled than in G. balzanii ; bases of dorsal and anal with few scales ; fold of the lower lip not continuous. A dark area across back in front of the dorsal ; bases of some COLLECTION OF FISHES FROM BUENOS AIRES 455 of the scales of the back frequently very dark brown ; side with about 6 cross-bands, each of those on middle of side composed of double dark lines with a band of light of equal width between them ; no dark spot on side ; pectoral light ; ventrals blue- black ; dorsal dusky, with ascending light stripes which are largely replaced by light spots on the soft dorsal ; caudal dusky, with round hyaline spots on the rays similar to those on soft dorsal ; anal with similar but smaller and less distinct spots ; no spot or ocellus on the caudal. Type in Mus. Princeton Univ., a specimen 155 mm. long, from Buenos Aires ; coll. Prof. W. B. Scott. Cotypes in Princeton and Indiana Universities (no. 11352, Mus. Ind. Univ.), 6 specimens 100 to 150 mm. long, from same locality. Batrachops scottii Eigenmann, new species. (Plate XXIII, Fig. 8). ? Crenicichla semifasciata Pellegrin (not Heckel) Cichlides, 339, 1904 (Buenos Aires; Montevideo). This species is closely related to semifasciata of Heckel, from which it differs conspicuously in color. B. semifasciatus was described from specimens collected in the Paraguay River at Caigara in Matto Grosso. No other specimens have been found unless those recorded by Pellegrin belong to semifasciatus. The two species may be distinguished as follows : a. D. xxii, 10; A. in, 7 ; lateral line 25+ 12; scales 56 or 57; greatest thickness 1.25 in greatest height which is 5 in the total length ; depth of caudal peduncle equals five eights of the greatest depth ; eye 1.5 diameters behind tip of lower jaw, 5.5 in head ; suborbital one third the diameter of eye ; peroper- cular margin turned forward ; a dark band from eye to opercle, 7 or S dark lines from base of dorsal to middle of side, darkest below lateral line and fading out below; a dark ocellus on base of caudal ; each scale of the side yellow, with a dark brown margin ; fins without spots, semifasciatus. aa. D. xxi or xxn, 13; A. in, S or 9; lateral line 25 + 14; scales 57; head 3.4 to 3.5 ; depth 4 to 4.5; greatest thickness 1.5 in greatest depth ; depth of caudal peduncle 2 in greatest depth; eye 2.5 diameters behind tip of lower jaw, 5.5 to 7 in the head ; preorbital 1 (in adult) to 2 (in youngest) in the eye ; peropercular margin slanting obliquely backward ; Proc. Wash. Acad. Sci., March, 1907. 456 E-IGENMANN tips of dorsal and anal reaching caudal ; a dusky shade from eye to edge of opercle continued faintly in the young to the caudal ; very conspicuous markings extending from eye down and ' back ; they consist first of a black blotch followed by two or four parallel black lines, these followed after an interval by one to 5 similar ones and these again in some specimens by other similar ones ; back to the lateral line in the young with very obscure cross shades ; side, and in the adult the back also, with light stripes along the middle of the scales and prominent zigzag dark stripes between each two rows of scales ; entire dorsal and base of anal spotted ; caudal ob- scurely spotted ; pectorals and ventrals plain. The black markings below the eye are so unique and con- spicuous that they attract the attention at once and give the impression of India ink pen strokes. I take great pleasure in dedicating this species to the collector, Prof. W. B. Scott, of Princeton University. Type in Mus. Princeton Univ., a specimen 280 mm. long, from Buenos Aires ; coll. Prof. W. B. Scott. Cotypes in Princeton and Indiana Universities (No. 11420, Mus. Ind. Univ.), 145 to 165 mm. long, from same place. PLEURONECTID^. Achirus lineatus (Linnaeus). Two specimens. 458 COLLECTION OF FISHES FROM BUENOS AIRES EXPLANATION OF FIGURES. 1-3. Plecostomns la f lata Eigenmann, type. 4-5. Loricaria vetula Cuvier & Valenciennes. 6. Pomolobus 7nelanostomus Eigenmann, type. 7. Geophagus australe Eigenmann, type. S. Batrachofs scotti Eigenmann, type. Proc. Wash. Acad. Sci., Vol. VIII. Plate XXI FIGS. 1-3. PLACOSTOMUS LAPLAT/E EIGENMANN, NEW SPECIES. Proc. Wash. Acad. Sci., Vol. VIII. Plate XXII. FIGS. 4 & 5. LORICARIA VETULA CUVIER & VALENCIENNES. Proc. Wash. Acad. Sci.. Vol. VIM. Plate XXI FIG 6. POMOLOBUS MELANOSTOMUS EIGENMANN, NEW SPECIES. W*^"^^^ w cms , fi&iS^r -^*»> _grf ax^^r 1£1- KhK^M^i FIG. 7. GEOPHAGUS AUSTRALE EIGENMANN, NEW SPECIES. FIG. 8. BATRACHOPS SCOTTII EIGENMANN, NEW SPECIES. PROCEEDINGS OF THE WASHINGTON ACADEMY OF SCIENCES Vol. VIII, pp. 459-486. pls. xxiv-xxviii March 6, 1907. HISTOLOGY AND DEVELOPMENT OF THE DIVIDED EYES OF CERTAIN INSECTS. By George Daniel Shafer. Exner, 1891, Zimmer, 1897, and Kellogg, 1898, 1900, and 1903, have discussed the divided-eye condition of certain crus- taceans and insects. It is the purpose of the following paper: 1. To describe the histological structure of the divided com- pound eyes of Sympetriim corrupta, Anax Junius, Dibio hirtus, two species of Blepharoceridaj and two species of CaHibcetis. 2. To describe the development of the large-facetted area of the eye in CaHibcetis and Sympctrum corrupta. 3. To refer briefly to the significance of the divided-eye con- dition in these eyes. This investigation was made in the Entomological Laboratory of Stanford University, under the direction of Prof. V. L. Kellogg. I wish here to thank Professor Kellogg, Mr. Doan and Miss McCracken for help in the laboratory ; also Professor Aldrich, Dr. Needham and Mr. Grinnell for identifying some of the material used. SYMPETRUM CORRUPTA Hagen. The compound eyes of Sympctrum corrupta, as shown in Fig. 1, Plate XXIV, are divided by a curved line into almost equal upper and lower parts. The lower half of the eye is dark and a good hand lens shows it to be made up of very small facets. The upper half is lighter in color and made up Proc. Wash. Acad. Sci., March, 1907. 459 46O SHAFER of larger facets. Longitudinal sections of the ommatidia of both these parts of the eye may be obtained by making vertical cross-sections, or by making longitudinal sagittal sections of the head. Fig. 2 shows a vertical section passing through both the upper and the lower portions of the eye. Most of the eye elements are cut longitudinally. A few in the region a, of the upper part of the eye are represented in diagonal cross-section. A glance at the figure makes clear the deeply pigmented condi- tion of the narrow eye elements of the lower half as contrasted with the less pigmented larger elements of the upper half of the eye. There is no gradual transition in the pigmentation or in the size of the eye elements. The line of division is as sharp within the eye as it appears in the outside facet view. No septum marks the division ; but with the first larger orama- tidial element, passing toward the upper part of the eye, the deep black iris pigment stops and a brownish less dense iris pigment begins. This is true also of the deeper seated pig- ments, but these are a little darker in color in the large element half of the eye than in the iris pigment in the same part. Figs. 3 and 4 show some of the details of structure of the upper and lower parts of the same eye. The corneal region is made up of hexagonal lens-like segments each of which maybe called a corneal lens. In vertical section each lens is seen to consist of a thin cuticular portion and a thicker stratified layer just beneath. The cuticular portion takes and retains nuclear stains well. The under portion takes stains readily enough but gives them up easily. No hypodermal cells or nuclei have been observed in the eye, but the bases of the pseudocones lie close to the under portion of the lens. The cells which compose these pseudocones have lost their identity entirely in the lower portions, and nearly so in the upper, outer, larger portion of the cones. However, in the extreme upper ends, the cone cells have each secreted a denser curved plate-like body within itself, and this stains deeply. Four of these may be found in each pseudocone. Two are shown in the longitudinal sections at en. Each plate appears to surround a cell nucleus. In the case of the pseudocones of the small ommatidial elements, cross-sections made just below the little plates mentioned show four cells as represented in DIVIDED EYES OF CERTAIN INSECTS 46 1 Fig. 3, B. Two of these cells are always larger than the other two. Two of the plates of the pseudocones are always larger when four are seen — sometimes only 2 can be found. The pseudocones of the large ommatidia are wider, longer and farther apart than those of the small ommatidia. Both have relatively the same shape. The inner portion of each pseudo- cone tapers nearly but not quite to a point. Each inner end is really truncate and appears to have a funnel-like opening. Extending along the line of the longitudinal axis of the pseudo- cone and beginning immediately beneath the truncate cone tip is the retinula. This has a darker rhabdome portion along the axis from the tip of the pseudocone to the basement membrane. The axis itself, however, is occupied by a very narrow light band. Often, if the sections are jammed a little in the cutting, the rhabdome portion takes a wavy form as shown in the frag- ment at iv (Fig. 4, A). The retinulae of the large ommatidia are wider, but no longer than those of the small ommatidia. Immediately beneath the basement membrane, in all parts of the eye is a network of tracheal vessels, 2 of which are shown in cross-section at tr (Figs. 3, A, and 4, A). Under the tracheal network is a narrow layer of retinular-like bodies rb (Figs. 3 and 4, A). These bodies have their long axes parallel with each other, but not always exactly parallel to the retinular axes above them. Some sections show a definite fibrous or continu- ous cell connection between the ends of the retinula at the base- ment membrane bm, and the upper outer ends of these retinular- like bodies. These connecting strands are always narrower than either the retinula or the retinular-like bodies, and they curve around the tracheae, often, in order to make the connec- tion. It seemed impossible to demonstrate the presence of retinular nuclei satisfactorily in old adult eyes used, but they were easily shown at rn (Fig. 4, A), in the eye of a young insect dissected from an old nymph case when the adult was just ready to issue. Here and there along the upper part of some cells of the retinular-like bodies large nuclei have been found («, Figs. 3 and 4, A). These nuclei appear larger than the ordinary pig- ment cell nuclei. Whether they have any special significance 462 SHAFER has not been determined. Cross-sections of the retinular-like bodies under the large ommatidia are shown in Fig. 4, B. Regularly, they appear as shown, with 4 cells — one large, 2 smaller and 1 very small cell. Cross-sections of the corre- sponding retinula above show that the separate cells there have almost lost their identity in the adult eyes ; but in the very young teneral adult 4 nucleated cells may be seen (Fig. 4, C) in cross-section. From the lower part of the retinular-like bodies extend branching tree-like nerve fibers which break up into brushes of fibrils at their inner ends. The pigment of the region of the small ommatidia may be described under 4 heads : 1. That grouped in dense black masses around the pseudo- cones and already named the iris pigment. It is contained in 2 kinds of cells called by Grenacher, 1879, primary and secondary pigment cells. The secondary cells are long, narrow and closely packed around and among the pseudocones — their axes lying parallel with the cone axes. Around cross-sections of the upper parts of the cones 20 to 22 of these pigment cells may be counted in a circle touching the outer boundary of the cone (Fig. 3, B, sip). In the sections near the inner tapering tip of the cone as few as 14 pigment cells have been counted touching the cone. Below that the separate cells could not be counted, but they are packed all the way between the different pseudo- cones, being densest on the middle plane of the cone. There are 2 chief pigment cells for each eye element. They are short and thin and the 2 encircle the cone tip (Figs. 3 and 4, A). 2. Pigment occupies the retinula and the cells between the retinula from the apex of the cones to the basement membrane. Beginning near the distal ends of the retinula this pigment becomes denser and denser toward the basement membrane until a plane (ee, Fig. 3, A), is reached a little below the mid- dle of the retinula. From this plane to the basement membrane the pigment is again less dense. 3. A band of dense black pigment lines the basement mem- brane and on the inner side of this membrane, extends down to the distal ends of the retinular-like bodies. It is densest immedi- ately beneath the basement membrane, around the trachea and DIVIDED EYES OF CERTAIN INSECTS 463 in a thin band, /, which marks its lower boundary along the dis- tal ends of the retinular-like bodies. 4. A black pigment similar to that along the retinula sur- rounds the retinular-like bodies, and ends at the proximal ends of these bodies in a narrow densely black band of pigment, gp (Figs. 3 and 4, A). This in Sicyonia sculpa, has been named the pigment or tapetum sheath of the optic ganglion by Exner, 1891. The same description of pigment holds for the large omma- tidial part of the eye except that the iris pigment and retinular pigment in this case are brownish yellow and everywhere in this part of the eye the pigment is very much less dense than in the small ommatidial region. ANAX JUNIUS Drury. The facets of the compound eyes of the male of Anax Junius are not all of the same size. Facets may be found that differ as much in size as those of the different areas on the eye of Sympetriim, but no line divides the eye of Anax into 2 regions. In this case the larger facets are found on the upper and inner surfaces of the eyes, and the smaller facets on the outer lower margins. The 2 sizes grade into each other. It was not until sec- tions were made of the eye that this condition was noticed. Fig. 12 was made from a cross-section of the head of a male Anax, cut in a plane passing through the ocellus and perpendicular to the facet area of the compound eye. The figure shows clearly this gradation of the large facets on the upper inner part of the eye into the smaller ones at the outer margin. As is shown also, along with this gradation in the size of facets, the elements of the ommatidia pass through a like gradation in size and length. Moreover, a similar but reverse condition holds for the pigmen- tation in this eye. Around the smaller shorter elements at the outer margin of the eye the pigment is densest and occupies the whole length of the retinula?. Passing toward the inner part of the eye, the pigment becomes less and less dense around the proximal ends of the retinula; until in the region of the largest ommatidia almost no pigment is present except the iris pigment. Other than this difference in size and pigmentation, the large and small ommatidia are very similar as may be seen in Figs. 464 SHAFER 13, A, and 14, A. Beneath the corneal lenses and lying above the distal ends of the pseudocones is a distinct hypodermal layer. In longitudinal section, two apparent nuclei are present above each pseudocone, sn (Figs. 13 and 14, A). The pseudo- cone itself has a structure similar to that of Sympetrium, its upper part showing still the boundaries of 4 cells which may be seen in cross-section (Fig. 13, C). Each retinula is made up of 4 retinular cells which enclose a single rod-like rhabdome, rb (Figs. 13, A and B, and Figs. 14, A and B). The retinular cells of the ommatidia from the 2 extreme parts of the eye described vary, somewhat in shape (as seen in Figs. 13, B, and 14, B) but there are always the 4 cells present, each with its nucleus (Fig. 13, B). Extending up be- tween the different retinulas and lying parallel with them are many open spaces or lumina (Fig. 13, A, I). The smaller ends of these extend even between the distal parts of the pseudocones and their surrounding pigment cells (Fig. 13, C, I). The iris pigment of this eye occupies cells of 2 types called by Grenacher and others the primary or chief pigment cells and the secondary pigment cells. Two primary pigment cells surround the small proximal end of each pseudocone (Figs. 13 and 14, A, cifi). These cells are shown as they appear in cross-section in Fig. 13, D, cfi. The nuclei of these cells have not been satisfactorily seen although the nuclei of the retinular cells and secondary pig- ment cells in the same sections were deeply stained and easily seen. Eight to 10 pigment cells have been counted around each pseudocone. They are longer and more slender than the primary cells around which they lie, and they extend down a little between the distal ends of the retinulas (Figs. 13 and 14 A, nsp). As has already been said, the pigmentation of the smaller outer elements of the eye occupies the whole length of the retinulge. This pigment lies in the retinular cells themselves, and it is densest always in the distal half of the cells. BIBIO HIRTUS Goef. The compound eyes of the male Bibio are much larger than those of the female. They nearly touch along the narrow front and occupy almost the entire head. The whole facet area is DIVIDED EYES OF CERTAIN INSECTS 465 thickly covered with slender hairs ' and the remarkable double character of the eyes may be easily overlooked. Indeed, it is only upon careful observation that the densely black, small, facetted area is seen at all. If the head of the fly is tilted back by lifting up the proboscis, a hand lens will show the narrow black small facetted area on the extreme ventral surface of the compound eye. This area is scarcely one sixth that of the entire eye and is separated from the large facetted upper surface by a narrow groove or offset. Fig. 11 shows the position of the small facetted part of the eye. Fig. 8, perhaps, shows better the relative extent of the 2 kinds of elements as seen in longitudinal sagittal section. As shown in this Fig. 8, the elements beneath the small facetted region are little more than half the length of those under the large facets. Moreover, the part occupied with small elements is densely pigmented. The rest of the eye has but little pigment. The elements of a large ommatidia consist of a thin cuticular hexagonal facet, a pseudocone, a retinula, and iris pigment cells surrounding the pseudocone. The cells of a pseudocone cannot be distinguished from each other in the outer large part of the cone. The lower truncate or slightly rounded apex of the cone is a little denser than its upper part and this denser portion stains more readily. Here the 4 cells making up the cone can be dis- tinguished, each having its nucleus (Figs. 9 and 10, c«, and Fig. 9, B). Cross-sections of the distal ends of 3 neighbor- ing retinula? are shown in Fig. 9, C. Each retinula is made up of 6 cells arranged in a circle around a seventh cell in the center. The inner borders of each of the 6 cells has a rounded deeply stained rhabdomere (as this part of the eye was named by Grenacher, 1879). The rhabdomere of the seventh cell oc- cupies the axis of the retinula. At their distal ends the 6 retin- ular cells overlap entirely the rounded denser apex of the pseu- docone, d (Figs. 9, A, and 10). The seventh cell, together with its rhabdomere and those of the other 6 cells, stop snugly against the inner end of the pseudocone. Near the middle part 1 Whether these apparent tactile hairs, which cover the eve of Bibio so densely and are found on the eye of Blephorocera less abundantly, are really supplied with tactile sense organs has not been determined bv me. 466 SHAFER of the retinula this seventh cell, which is entirely surrounded at its distal end, is found squeezed out between the other 6 retinular cells and is not here completely surrounded by them (Fig. 9, £). This condition holds for the retinula for its entire proximal half. It is true also that this seventh cell crops out in every case on the same side of the retinula, namely, on that side of the re- tinula turned toward the inner ventral angle of the eye. Fig. 9, D, shows 3 adjacent retinulae in cross-section in the region of the nuclei. These nuclei are long-elliptical in shape (Fig. 9, A, rn), and in cross-section they are not all the same size, since some are cut near the middle and some near their ends. In the cross-section of every retinula, however, the nucleus of the narrow seventh cell may be found near its outer margin (Fig. 9, Z>, 7«). The rhabdomeres are all smaller at the prox- imal end of the retinula, but they are always 7 in number, the odd one occupying the axial position at the inner part of the narrow seventh cell. These facts, taken with that of the con- stant presence of the seventh nucleus, make it certain that this peculiar seventh structure is truly a retinular cell whose distal end is entirely surrounded by the corresponding ends of its 6 companions. The proximal ends of the retinulae are bounded by a very thin basement membrane, bm (Figs. 9, A, and 10). A little beneath this membrane spreads a somewhat thicker granular tapetum, tp (Figs. 9 and 10), and immediately under this is a network of tracheae, tr. Leading from the inner prox- imal end of each retinula through the basement membrane, the tapetum, and between the tracheae is a narrow bundle of nerve fibers, which are soon lost in a fine granular layer, gr (Figs. 9, A, and 10), just within the trachial network. The iris pigment of the large element part of the eye is com- paratively slight. It is contained in narrow pigment cells, nsp (Figs. 9 and 10), which surround the pseudocones and extend a little way down between the retinulae. Fig. 9, C, sip shows the arrangement of these cells between the retinulae. The proximal three fourths of the retinulae have no pigment cells around them at all and the retinulae themselves touch each other (Fig. 9, D). The conditions described above also hold for the small eye DIVIDED EYES OF CERTAIN INSECTS 467 elements with the following exceptions. The cuticular facets of this portion of the eye are much denser than those above the large elements. The iris pigment is black and extremely dense. A heavy black pigment occupies the retinular cells throughout their entire length. Drawing 10 was made from a section that had been depigmented with cone, nitric acid and absolute alcohol, equal parts. The tapetum and the basement mem- brane in this part of the eye are always a little farther apart than in the large element region. Under the trachea and between the nerve strands that lead down from the retinulse of both the large and the small elements are numerous large round or oval nuclei which stain deeply {gn, Figs. 9 and 10, A). No pigment is present around these nuclei. It might be added here that cross-sections of the retinulae of the small ommatidia did not show the number of retinular cells present so clearly as those cut across the large ommatidia. Judging from the num- ber of retinular nuclei however, the number of retinular cells is the same in the retinular of both regions of the eye. 'BLEPHAROCERA CAPITATA Loew. Kellogg, 1903, has called attention to the fact that both males and females of the Blepharoceridas have divided compound eyes. In all the genera described by Kellogg the large facetted area of the eye is dorsal, and the small facetted deeply pigmented area of the eye is lateral. Moreover, the dorsal area of the female eye is greater than that of the male. Males and females of species representing 2 genera (Blcpharocera capitata and Bibioccfihala elcgantulus) were studied by me. The histolog- ical structure of the eye elements in the 2 genera and in both sexes is practically the same. The description and drawings given here are taken from Blefiharocei'a capitata. Fig. 30 is a microphotograph showing the optic ganglion, as well as the dorsal and the lateral eyes of the right side of the head of this species. It will be convenient hereafter to speak of the two areas as the dorsal and the lateral eyes since they are separated from each other by a narrow but distinct groove and the outer lobes of the 1 1 am glad to make reference to a recent preliminary note on the " Morphol- ogy and Development of the Divided Eyes of Blepharocerca tenuipes'1'' by Dr. Wm. A. Riley, in Science, Sept. 7, 1906. 468 SHAFER optic ganglion beneath each area are distinct. The corneal lenses over the greater part of the dorsal eye have been torn from this section. The remaining 2 entire elements, however, show the ommatidia in this dorsal eye to be about two and a half times the length of those in the lateral eye. The lens and the pseudocone of a dorsal ommatidia are continuous. That is, the inner surface of the corneal lens is not noticeably separated from its adjoining cone beneath. This is easily seen in micro- photograph 29 and Fig. 15. The rounded apex of each of the pseudocones is denser than the rest of the cone and stains readily. Cross-sections through this denser apex show the cone to be made of 4 cells and the nucleus of each cell is found in this denser part (Fig. 15, A). In the outer larger part of the cone the cell walls cannot be distinguished. Surrounding the tip of each one are 2 very thin primary iris pigment cells (Fig. 15, A, ci-fi). Outside of these, sheathing the distal part of each cone and extending down between the retinulae are 22 to 24 slender secondary pigment cells (Fig. A, sip, and Fig. 29, sip). A retinula in this eye is composed of 7 cells — 6 entirely surrounding the seventh for its entire length. The rhabdomere of each cell is distinct (Fig. 15, C, rb). The distal ends of the retinular cells abut closely against the rounded cone tip and in their extreme proximal ends just above the basement membrane, lie the 7 large retinular nuclei (Fig. 15, A, rn). A definite bundle of nerve fibers leads from the base of each retinula through the basement membrane (Figs. 15, A and 29, nj). The number and position of the cells in the ommatidia of the lateral eye of this fly is the same as that just described for the dorsal eye. The corneal lenses of the lateral eye are more distinctly formed and the retinular cells as well as the iris pig- ment cells (primary and secondary) are densely packed with pigment. In the dorsal eye the pigmentation in the iris is very slight and it is absent in the retinular cells of this eye. CALLIByETIS HAGENI Etn. Several references have already been made by different investigators to the condition of the compound eyes of certain mayflies (Pictet, 1845; Ciaccio, 1880; Carriere, 1893; and DIVIDED EYES OF CERTAIN INSECTS 469 Zimmer, 1897). The large facetted dorsal eyes have been called turban eyes and the smaller deeply pigmented eyes, the lateral eyes. The females have only the small lateral pigmented eyes. Zimmer, 1897, has given the histological structure of the eyes of 7 genera of mayflies according to Pictet's classification and he discussed also the physiological significance of the turban eyes of these insects. The structure of the eyes of Callibatis hageni differs in only a few points from that given by Zimmer for Cloe fuscata Pict. It will be well, however, to describe briefly the structure of the eye in the adult male of Callibcetis hageni before taking up the development of the turban eye in that species. Microphoto- graph 24 (a cross-section through the head) shows the relative size, position, pigmentation and the general structure of the right turban and lateral eyes. The large and small eye ele- ments are entirely separated here by a deep, rather wide, groove. A single partly divided optic ganglion lies beneath the right turban and lateral eyes and a similar ganglion beneath the left eye o-pg in Figs. 23, 25 and 26. Drawings in Fig. 16 show more clearly the structure of 2 entire elements of the turban eye. The light-gathering or dioptric apparatus consists of a corneal lens, 16 Ac, a cone, Aco, and a hypodermal space between the lens and the cone, 16 Ahs. The cornea is made up of rather distinct convex lenses, Ac, which are continuous with each other. The outer third of each of these lenses appears to be denser than the inner two thirds. The cone is composed of 4 crystaline bodies so closely associated along their inner faces that they appear in all except cross-sections as one solid cone body with its slightly convex base facing the cornea. This is the eucone type of Grenacher, 1879. The outer faces of each crystaline body are surrounded by the less dense protoplasm of the mother cone cell and in this protoplasm just distal to the base of the cone are the cone cell nuclei (Fig. 16, A, en). The cross-sec- tion made just distal to the cone base B, shows the 4 cone cells and their nuclei. The hypodermal space contains no nuclei, and it is filled by transparent fluid only. Zimmer demonstrated 2 nuclei in this space for Cloe. He did not figure the nuclei in this space for the eye of Bcetis cerea Pict., or for that of Chiro- 470 SHAFER tonetes ignotus Walk., but speaks of the space nevertheless as being formed by 2 hypodermal cells. Closely surrounding the entire length of the cone cells and the hypodermal space are 20 to 22 secondary pigment cells (Figs. 16, A, nsfi and B, sip). No primary pigment cells are present. The distal ends of the secondary pigment cells touch the cornea and their proximal ends are in contact with the outer or distal retinula (Fig. 16, A, dm). It is proper to speak of a distal retinula in this eye because there is also an inner or proximal retinula -prn in each ommatidia — the 2 retinular parts being connected by a very delicate strand (rs, Fig. 16, A). Both proximal and distal retinulse are composed of 7 retinular cells. Fig. 16, C, shows the 7 short distal retinular cells and their nuclei. These cells surround the tip of the cone rosette fashion. The proximal retinula is of about the same length as the connecting strand. Fig. 16, D, shows the 7 nucleated cells of this part in cross-section, and Fig. 16, E, is a similar section near the middle part of a proximal retinula. The rhabdome in its cross-section here is seen to be a 7-pointed star within a circle which bears on its circumference 7-knobbed projections, zv, radiating along the same lines as the points of the star and lying between the boundaries of the retinular cells. The knobbed parts, zv, are the secondary rods of Zimmer, 1897. This large surfaced rhabdome terminates a little short of the outer end of the proximal retinula in a single blunt rod tip as shown in Fig. 16, D. The outer end of the retinula therefore appears filled with transparent liquid. Zimmer has described these transparent ends in Cloe as " bladder trachea," and he figures no nuclei in them. My sections of the turban eye of Callibcetis show the 7 nuclear structures present always, as represented in Fig. 16, D. The inner faces of the distal retinular cells bear an extremely thin rhabdome plate next to the tip of the cone (Fig. 16, C, drb). Near the distal ends of the proximal retinula the connecting strand, rs, breaks up, Fig. 16, A, into smaller strands which seem to be continuous with the 7 secondary rods, zv of Fig. 16, E. The connecting rods may be seen in the photograph no. 27. The space around the rods, between the distal and proximal ret- inulce, appears to be filled with an almost transparent liquid — DIVIDED EYES OF CERTAIN INSECTS 47 1 tiny pigment granules being present in some sections. But these may have been carried there by the razor. Upon the basement membrane are short pigment cells which are sometimes above the membrane between the proximal ends of the retinulae ; some- times beneath the membrane between the nerve fibers, nf\ and sometimes partly above, partly beneath the membrane. A second delicate membrane k marks the lower limit of migration of this pigment. Fig. 17, A and B, show the structure of two ommatidiae in the lateral pigmented eye of Callabcctis. One of the elements is represented in its normal pigmented condition, the other de- pigmented so that the position of nuclei maybe seen. The cor- neal lenses in this eye are thin as compared with the turban eye and their inner faces fit snugly upon the distal bases of the cones. These cones are not as dense as those of the large elements just described. They are 4 in number, however, and appear to have the same density throughout. The cone cell nuclei en, are found in the extreme distal base of the cone. In depig- mented sections the nucleated distal ends of the retinular cells may be seen touching the tip of the cone. There are 7 of these retinular cells surrounding the rod-like rhabdome as represented in Fig. 17, B. No primary iris pigment cells are present, and there are but half the number of secondary pigment cells found in the turban eye. The 11 cells (Fig. 17, B), which are present, however, are densely pigmented, and they overlap the cones and the upper retinular. The retinular cells are deeply pig- mented through their entire length. Just beneath the basement membrane is a narrow almost transparent granular tapetum and under that an irregular broader band of pigment. So far, this pigment has not been observed above the basement membrane in the lateral eye. Nerve fibers «/"(Fig. 17, A) lead from the inner ends of the retinula through the tapetum and the under- lying pigment. Another species of Callibcet/'s (probably californica) was studied in connection with hageni. The latter is the larger of the 2 species but the eye structure of the male of this smaller form differs from that just described for hageni in but two par- ticulars that are worth attention : Proc. Wash. Acad. Sci., March, 1907. 472 SHAFER 1. The cornea of the turban eye of the smaller species is thinner and its lenses less convex than those in C. hageni. 2. The retinular connecting strands in the eye of the smaller species are about one and one third times longer than the prox- imal retinulee. That is, the strands in this species are relatively a third longer than they are in the eye of C. hageni. DEVELOPMENT OF THE LARGE FACETTED EYE AREA (TURBAN EYE) IN CALLIB^STIS Etn., AND IN SYMPETRUM CORRUPTA Hagen. As is well known, the young of dragonflies and mayflies pass through incomplete metamorphoses in their post-embry- onic development, and the young of both live in fresh water. Young nymphs of both species of Callibcetis and of S. cor- rufita were collected from still or slowly running water near Stanford University in March and reared to the adult stage in the laboratory. In this way material was obtained representing different stages in the development of the large facetted-eye areas. Carriere, 1886, first briefly called attention to the origin of the elements of the turban eye of mayflies from elongated epithelial cells near the dorsal edge of the lateral eye. His observations in the main agree with the following account. All nymphs of Callibcztis under 4 mm. in length have only lateral pigmented eyes. When the nymphs are 4 to 5 mm. long however, the lateral eyes have about completed their develop- ment. Then a narrow yellowish or light brown band appears above the dorsal edge of each lateral eye of the male nymphs. This marks the first noticeable beginning of the large facetted eye, and cross-sections made of the head of such a nymph show the hypodermis, just beneath the light brown band, to be made up of modified long slender hypodermal cells with a second layer of much shorter cells lying against their inner bases. Already 2 membranes very close together are forming here. One of these membranes (Fig. 21, A, k), marks the inner bound- ary of the second layer of cells A, 2J111. The other membrane A, dm, marks the inner boundary of the outer layer of modified long hypodermal cells. The nuclei of some of the cells of the second layer are above the membrane A, bm, and some are DIVIDED EYES OF CERTAIN INSECTS 473 below it. These 2 membranes were found also beneath the developing unpigmented ommatidia in the upper eye of young S. corruptee (Fig. 7, A, bm and k, and Fig. 6). The upper membrane is found throughout the further development of the eye and corresponds to the basement membrane of the adult. The lower membrane, k, seems to be identical with the limiting membrane, l\ of the lower pigment cells in the adult eye (Fig. 16, A). This second layer of cells (Fig. 21, A, 2/in), then, ap- pears to be that from which developed the lower pigment cells of the adult eye. If that is true, it is clear how it is possible for those pigment cells to migrate up and down through the basement membrane in the adult eye since that membrane is formed, in the beginning, at the inner ends of the outer hypo- dermal layer of cells (Fig. 21, A, ihn), around these developing pigment cells A, zhn, not as an entire or closed membrane above them. In cross-sections of the head made at a little later stage of de- velopment, cells of this upper modified hypodermal layer just de- scribed are found to be differentiating into an outer and an inner layer so that 2 rows of nuclei may be seen above those which lie along the basement membrane (Fig. 21, B, if a). Long undi- vided hypodermal cells may still be seen, however, at the edges of this developing turban eye, Fig. 21, B, x, next to the normal hypodermis, and at y, next to the dorsal edge of the lateral pig- mented eye. In a still later stage of development (Fig. 22) the cone cells and the secondary iris pigment cells are found occu- pying the position of the outer row of nucleated cells described in Fig. 21, B, opposite x. The retinulae, each already definitely formed of its 7 cells occupies the position of the second row of nucleated cells in Fig. 21, B, opposite o. Here again the ele- ments in the middle of the developing eye (Fig. 22, ifa) are easily recognized as the older elements. Younger elements at the edges, x andjy, are seen much below the cornea. At each molt of the growing nymph these newer elements at the margin of the eye rise to their normal position under the cornea and thus increase the size of the eye. Fig. 22 represents the stage of development of the turban eye when the nymph is 8 to 9 mm. long. The pigmented eye has practically the same size as that in the 5 mm. nymph. 474 SHAFER None of the sections offers definite proof as to how the group of 7 retinular cells or, of the 4 cone cells, in a single element arise — whether by multiplication of a single mother cell to form each retinula for example, or by association of the original mother cells into groups of cells. The secondary pigment cells however, seem to be homologous or identical with some of the original long hypodermal cells of the first upper hypodermal layer (Fig. 21, A, ihn). The evidence for this is very strong at least, in the young nymph eye of S. corrupta. Fig. 7, A, shows a single developing ommatidia from the unpigmented area of the eye of a young nymph. In this eye, some of the cells of the first hypodermal layer separate into upper and lower parts, the latter giving rise to the retinular layer as in C. hageni. The upper part then becomes two-layered again and cells of the lower of these layers (Fig. 7, A, nfic) become chief pigment cells ; the upper, gives rise to the cone cell layer A, en. Other cells of the first hypodermal layer appear simply to elongate. They grow very little and are seen surrounding the cone, chief pigment cells and retinular elements at A, nsfl. These elongated dor- mant cells lie in the position of the secondary pigment cells in the adult eye. Fig. 7, B, shows 2 elongated hypodermal cells from the developing margin of the eye (Fig. 6, x). They are almost identical in size and shape with what are evidently sec- ondary pigment cells in Fig. 7, A, nsj>. As development goes on, the young short retinulas lengthen rapidly. In the 9 mm. stage of development of the Callibaztis nymph, the rhabdomes are found as round rod-like bodies in all the older middle retinulas. By the time the sub-imago is ready to issue, the cones have all practically finished development. A few very small undeveloped cones are found around the outer margin, but most of these remain still undeveloped in the adult. Photographs 23 and 25 are made from cross-sections of the heads of sub-imagoes. The turban and lateral eyes are so definitely formed here that one might suppose development complete. Fig. 18, A, shows the structure of 2 ommatidia in a turban eye of a sub-imago of C. hageni. The corneal lens is definite but thin. The retinulas are slightly constricted just beneath the tips of the cones. In the cross-section (Fig. 18, B) DIVIDED EYES OF CERTAIN INSECTS 475 the rhabdome is seen to be star-shaped with the " secondary rods " beginning to develop between the boundaries of the retinular cells. Fig. 19 shows the structure of the turban eye elements of an old sub-imago of C. caltfornica — i. e.y just before time for the adult to issue. The cornea is still thin, but the secondary pigment cells have pushed it up a little and the distal ends of these cells may be seen overlapping the bases of the cones between c and en (Fig. 19). The retinula is now more nearly pinched into two. I was unable however, to demonstrate the presence of any nuclei in this retinula of the sub-imago below the constriction (d, Fig. 19) as might perhaps be expected. Otherwise the preparation for the separation of the distal and proximal retinulas and for the formation of the hypodermal space seems complete in this stage of the development. It is wonderful to see the rapid enlargement of the turban eyes as the adult issues from its sub-imago stage. Sub-imagoes issue from the nymphs in less than 3 seconds. The process for the adults is longer — 40 to 60 seconds — but the head enlarges immediately upon breaking through the chitin, and the turban eyes expand almost to bursting with a liquid. When photo- graphs 24 and 26 of the adult eye are compared with 23 and 25 of the sub-imago or drawing 16, A, with drawing 19, it is clear what happened to permit the enlargement. The secondary pigment cells which overlapped the bases of the cones have straightened up. The cornea has been lifted to permit this and thus the hypodermal space is formed — being bounded by the cornea, the cone and the surrounding secondary pigment cells. The liquid contents of this space and the secondary pigment cells together, undoubtedly secrete the thicker corneal lens of the adult eye. That is to say, the hypodermal space is anal- ogous to a cell in this eye, but it is in no sense homologous to a cell as is shown by its origin. Furthermore, the space between the distal and proximal retinulae is to be directly associated with the rapid expansion of the eye of the issuing adult. The narrow connecting portion of the retinula of the old sub-imago (Fig. 19) has been stretched to form the connecting strands of the adult. It must be observed here also that the proximal retinulse out- number the distal in the old sub-imago and in the adult. The 476 SHAFER extra retinulae are found in a ring around the outer margin of the eye. This has been noted by Pictet, and figured by Zimmer, 1897, and named by them the " abkonical ring" in the adult eye. Fig. 20 shows the structure of 2 ommatidia from the turban eye of an unidentified mayfly. It has primary pigment cells. No adults of this species were reared, but the development of the eye up to the sub-imago stage is, in general, identical with the development of the eyes just described. TABLE OF MEASUREMENTS OF DIVIDED-EYE ELEMENTS. Small pigmented Ommatidia. Length. Greatest Diameter. Greatest Thick- ness. Large Ommatidia. Length. _ , ! Greatest Greatest Thick. Diameter. Corneal lens Hypodermal space. Cone Entire retinula Proximal retinula. 0.348 1.268 I 0.07 I measured along the cone axis. 0.095 0.44 .07 2-73 1. 18 0.125 ness. mm. 1. Symfetrum corrupta Hagen. 0.728 4 0.546 0-273 1 o-395 1 0.728 1.82 I 0.546 4 -5 2. Anax Junius Drury. Pseudocone 0.32 1.09 0.205 4-5 0.36 i-5 0.45 6 3. Bibio hirtus Goef. Retinula 0.348 0.65 0.19 .18 0.507 i-54 0.327 o-3 4. Blefharocera capitata Loew. Lens and pseudocones — Retinula 0.3 •507 0.2 ,18 0.7 i-33 0.42 •39 5. CallibcBtis /lagetn' E,tn. 0.158 0.19 6. Callibcetis calif or?iica Banks. Cornea Hypodermal space. Cone Entire retinula Proximal retinula.. measured < 0.07 ilong the cone axis. °-35 0.9 0.-568 0.124 1.23 •05 3-8 1.26 .11 0.09 .126 DIVIDED EYES OF CERTAIN INSECTS 477 In an eye like that of Anax where the large elements in one part of the eye pass gradually over into smaller elements in another part of the eye, both kinds of elements seem to develop from the same center — the smaller elements being the last formed. As has been shown in the 2 divided eyes studied {Callibcetts and Synvpetrum) the large ommatidial elements begin develop- ment after the pigmented lateral eye is complete. In this case the optic ganglion which has already been formed for the pig- mented eye appears to bud or enlarge to receive the nerve fibers of the new eye elements. To support statements already made and for further reference the accompanying table of measure- ments of the eye elements of the different eyes studied is given. SIGNIFICANCE OF THE DIVIDED EYE CONDITION. Exner, 1891, has shown that an eye with a structure like that of the turban eye of Callibcetis (adult) is capable of forming an image of superposition upon the proximal retinulas as well as an image of apposition upon the distal retinulae. By means of this repeated formation of images upon the retina, the eye with the superposition image is enabled to see, even if somewhat indistinctly, in dim light where the small facetted deeply pig- mented eye could not see at all. Zimmer has shown that this is of advantage to the mayflies in mating, since the males seek the females on the wing in the twilight. In the case of all the other large facetted eyes discussed in this paper, an image of superposition would be impossible, since the retinulae in every case lie rather close together and are not divided into proximal and distal parts. In everv eye however, the increase in the size of the dioptric apparatus accompanies the decrease in pigmentation. Both of these conditions favor the admission of more light. This would admit of a better appo- sition image being formed in dim light. The small dioptric ap- paratus and dense pigmentation accompany each other and both favor the formation of a distinct apposition image in extremely bright light. Whatever the special adaptation then, the divided condition of the eyes may be regarded as an adaptation of dif- ferent parts of the eye to suit different intensities of light. 478 SHAFER Moreover, it would be of as much advantage to increase the sensitive receiving surface (rhabdome surface) in the eye used in dim light as to increase the dioptric or light gathering sur- face. The complicated rhabdome surface of the turban eye of Callibcetts shows this increased sensitive surface and further- more, the retinulae of the " abkonical ring " each have well de- veloped rhabdomes. The rhabdomes of the larger ommatidia of all the divided eyes are larger than those of the small ommatidia. Stanford University, April 28, 1906. LITERATURE CITED. Exner, S. 1891 Die Physiologie der Facettirten Augen von Krebsen und Insecten. Leipzig u. Weine Grenadier 1879 Untersuchungen iiber das Sehorgan der Arthropoden, Insbesondere der Spinnen, Insecten und Crustacean. Gottingen. Zimmer, C. 1897 Die Facetten Augen der Ephemeriden Zeit. f. Wiss. Zool.. Bd. LXIII, pp. 236-262. Kellogg, V. L. 1898 The Divided Eyes of Arthropods. Zoolog. Anzeig., Vol. 21, pp. 280- 281. 1900 Notes on the Structure and Life-history of Blepharocera capitata Loew. Ent. News, Vol. II, pp. 305-318. 1903 Net Winged Midges of North America (Blepharoceridse). Proceedings Cal. Association of Science, 3 series, Zool., Vol. Ill, No. 6. Pictet 1843 Histoire naturelle des Insects NeVropteres. Famille des Ephemerines. Geneve, 1845. Eaton 1888 Monograph of recent Ephemeridae or Mayflies. Trans. Linn. Soc. London, 2 series, Vol. Ill, Zool. Carriere, J. 1893 Kurze Mittheilungen aus Fortgesetzten Untersuchungen liber die Se- horgen. Zool,, Anz. IX. Ciaccio, G. V. 1880 Sopra la Notomia Minuta Degli Occhi Delia Cloe diptera. Reviewed in Journal of the Royal Mic. Soc, 1882, II, p. 609. EXPLANATION OF FIGURES. The sections from which the following drawings and microphotographs were made were cut 3 to 6 microns in thickness. They were stained either with Haedenheim's iron hematoxylin or by a modified Weigert's hematoxylin method. Some sections were cross-stained with good results by safranin in DIVIDED BYES OF CERTAIN INSECTS 479 analin. Depigmentation was done with absolute alcohol and C. P. nitric acid, equal parts, mixed. Killing of live material was done with best results in hot Gilson's fluid. The drawings were outlined with a camera lucida. Abbreviations not found in the following list are explained in the text itself. c. Corneal lens (cornea). en. Cone-cell nucleus. tr. Trachea. Bm. Basement membrane. rn. Retinular nucleus. nsp. Nuclei of secondary iris pigment cells. sip. Secondary iris pigment cell. Ifa. Large facetted area (dorsal eye). sfa. Small facetted area. tp. Tapetum. opg. Optic ganglion. cip. Chief iris pigment cell. up. Dorsal part of the head. rb. Rhabdome (rhabdomere). sn. Semper's nuclei in hypodermis. co. Cone or pseudocode. nf. Nerve fibers leading from retinula. Its. 1 lypodermal space. dm. Distal retinula nuclei. prn. Proximal retinula nuclei. rs. Connecting retinular strand. h. Tactile hair. ce. (Esophagus. tb. Turban or dorsal large facetted eye. la. Lateral pigmented eye. /Is. Transparent liquid space around the connecting strands. drb. Rhabdome of the distal retinula. PLATE XXIV. Figs, i to 7. Male of Sympetrum corruption Hagen. Fig. 1. Head of adult showing relative size and shape of the large and small facetted areas, X 8. Fig. 2. Cross-section of the right eye of adult, X 34- Fig. 3. A. A few elements from the small facetted deeply pigmented part of the eye (adult), X I4I- B. Cross-section of a cone and its surrounding secondary pigment cells from A, X 500. Fig. 4. A. Ommatidia from the large facetted part of the eye of 6". corrupta, XHi- B. Cross-section of three of the rhabdome-like bodies, rb of 4, A, X 5°°- C. Cross-section of the retinula in the region of the nuclei from Fig. 4, -4, X 385- Fig. 5. Head of a male nymph 51. corrupta, showing the triangular large facetted area forming. Fig. 6. Cross-section of one eye of Fig. 5. Fig. 7. A. A single ommatidial element from the developing large facetted area of a nymph of S. corrupta, X 3^5- B. Two of the upper modified hypodermal cells from the margin x of Fig. 6, X 3S5- Figs. 8 to 11. Eye of male Bibio hirtus Goef. Fig. 8. Longitudinal sagittal section of right eye, X4i« Fig. 9. A. Three ommatidia from the large facetted area, X 2°5- B. Cross-section of cone tip through cone nuclei and surrounding secondary pigment cells. C. Cross-section of three retinulae near their distal ends. E. Cross-section of a retinula near its middle. D. Cross-section of three retinula; in region of retinular nuclei. 4S0 Proc. Wash. Acad. Sci., Vol. VIII. Plate XXIV. PLATE XXV. Fig. io. Ommatidia from the small facetted pigmented area of male Bibio eye, X 9°o- Fig. ii. Head of male Bibio hirtus. Figs. 12 to 14. Eye of Anax Junius, Drury. Fig. 12. Cross section of a single eye of adult, X 4T- Fig. 13. A. Two ommatidia from the upper largest facetted part of the eye, X102. B. Cross-section of the retinula through the nuclei. C. Cross-section of cone and surrounding secondary pigment cells and lumina. D. Cross-section of cone tip showing surrounding primary or chief pigment cells and secondary pigment cells. E. Cross-section of three retinula? and enclosed lumina. Fig. 14. Two ommatidia from the smallest facetted part of the eye, X I02- Fig. 15. Eye of Blepharocera capitata Loew. A. Two ommatidia from the large facetted division of the eye (dor- sal), X 205. B. Cross-section through tip of cone showing four cone cells with their nuclei and the surrounding secondary pigment cells. C. Cross-section of a retinula showing the rhabdomeres. Fig. 16. Adult eye of a male Callibcetis hageni Etn. A. Two entire ommatidial elements from the turban or dorsal eye and parts of two proximal retinulse whose corresponding cone elements are not shown, X 385- B, C, D, and E. Cross-sections of corresponding parts of Fig. A as indicated by the lines. 48 2 Proc. Wash. Acad. Sci., Vol. VIII. Plate XXV. yl it'"'' i f s 14 -Mf- ■ :■■■ r . PLATE XXVI. Fig. 17. A. Two ommatidia from the lateral pigmented eye of adult male C. hageni Etn. One element is represented as depigmented, X 385. B. Cross-section of retinula of A. Fig. 18. A. Two ommatidia of a turban eye of a male subimago of C. hageni Etn. B. Cross-section of retinula of A. Fig. 19. Two ommatidia from the turban eye of a male subimago of C. cali- fornica Banks. An old subimago just before adult was ready to issue, X38.S- Fig. 20. Two ommatidia from the turban eye of male subimago of a mayfly of unknown species showing chief pigment cells. Adult of this species was not reared. Figs. 21 to 22. Eye of nymph of C. hageni Etn. Fig. 21. A. A small part of the earliest developmental stage of the turban eye of C. hageni observed. B. Entire eye of a young male nymph at a little later stage of develop- ment than A, i. e., nymph 5 mm. long, X 120. Fig. 22. Entire eye (turban and lateral) of a male C. hageni nymph S to 9 mm. long, X I2°- 4S4 Proc. Wash. Acad. Sci., Vol. VIII. Plate XXVI. 18 ■ V wm * 17 y k ■ - ' - i - PLATE XXVII. MlCROPHOTOGRAPHS. Fig. 23. Cross-section of head of subimago of male C. hageni. Fig. 24. Cross-section of a head of adult male C. hageni. Fig. 25. Cross-section of head of subimago of male C. calif ornica. Fig. 26. Cross-section of male adult of C. califomica. Fig. 27. Cross-section of part of large turban eye of an adult male C. hageni, showing the connecting strands between the proximal and distal retinula;. Fig. 28. Microphotograph of cross-section of head of an old nymph of .S. corrupta, the adult of which was about to issue. The section passes through the edge, only, of the pigmented part of the eye which in its largest part was about equal to the upper large facetted area as is shown by the size of the optic ganglion. Fig. 29. A few ommatidia from the dorsal eye of a female B. capitata. Fig. 30. Left dorsal and lateral eyes of a female B. capitata showing optic ganglion also. Most of the cornea of the dorsal eye is torn away. See Fig. 29. 486 Proc. Wash. Acad. Set., Vol. VIII Plate XXVII. QD.8. INDEX. Note. — New names in black-face type, synonyms in Italics. For index to paper on "Aspects of Kinetic Evolution " by O. F. Cook, see pp. 400-403. Acestorliampbus brachycephalus 454 ferox 454 hepsetus 454 Achirus lineatus 458 Acipenser 48 Acrostichum yoshinagai 146 Aerial Locomotion 407 Age of the Pre-volcanic Auriferous Grav- els in California 405 albicans. Pimelodus 452 albida, Rhus 194 Allen, Wm. F. 41 alleni, Cambarus 18 alternatus, Crossaster 131 Ami a 42 Amiatus 42 Amphilestes 98 Anasterias 136 Anaxjunius, compound eye of 463 angustiloba, Aralia 406 anomalus, Leptychaster 115 anus, Loricaria 453 Aplodinotus grunniens 52 pppendiculata, Frullania 159 aprica, Rhus 193 Aralia angustiloba 406 whitneyi 405 arbuscula, Rhus 184 arcticus, Leptychaster 112 areolatus, Cambarus (Cambarellus) mon- tezumae 23 argentinensis, Atherinichthys 455 arguta, Rhus 192 ashei, Rhus 179 aspera, Henricia 127 asplenifolia, Rhus 196 Asterias sanguinolenta 127 asthenosoma, Luidia 124 Astropecten 118 Astropecten californicus 118 erinaceus 118 fragilis 120 ornatissimus 119 regalis 121 rubidus 121 verrilli 121 Astropectinidce 112 Astyanax rutilus 454 Atherinichthys argentinensis 455 bonariensis 455 Atherinidse 455 atrovirens, Rhus 182 auriculata, Rhus 17S Auriferous Gravels in California, Age of the Pre-volcanic 405 australe, Geophagus 456 autochthon, Heros 456 Ba;tis cerea 469 balzanii Geophagus 456 Barb 68 barbatus, Cambarus 18 Bathybiaster 114 Batrachops scottii 457 semifaseiatus 457 Bell, Alexander Graham 407 bellona?, Ludwigia 114 Bematiscus 93 Bibio hirtus, compound eye of, 464 Bibiocephalus elegantulus 461 Bilobed hypsodont stage of molars 99 bisseti, Ptilidium 141 blandingi, Cambarus 18 Blepharocera capitata, compound eye of, 467 tenuipes, compound eye of, 467 bonariensis, Atherinichthys 455 borealis, Crossaster 134 borealis, Rhus 188 Brachiolejeunea gottschei 157 sandvicensis 157 brachycephalus, Acestorhampus 454 Brachyodont tricodont stage of molars 99 brevis, Scapania 160 brevispiua, Luidia 121 Buenos Aires, On a Collection of Fishes from, 451 californica, Calliba?tes 471 Laurus 405 Luidia 121 Juglans 406 Magnolia 405 Ulmus 406 californicus, Astropecten 118 californicus, Rathbunaster 137 californicus, Sabalites 405 Callibaetes californica 471 hageni 468 Cambarellus 19 Cambari, Mexican, Central American and Cuban 1 Cambarus alleni 18 barbatus 18 blandingi 18 clarki 24 4S7 488 INDEX Cambarus clypeatus 18 consobrinus 12 evermanni 18 hinei 18 montezumae 2 shufeldti 24 tridens 19 williamsoni 10 (Cambarellus) chapalanus 22 montezumae 19 areolatus 23 dugesi 20 occidentalis 20 tridens 20 (Cambarus) wiegmanni 20 (Paracambarus) paradoxus 3 (Procambarus) cubensis 11 digueti 21 mexicanus 11 pilosimanus 6 capitata, Blepharoeera, compound eye of 467 caroliniana, Rhus 181 Carp 69 Cavicularia 141 cavifolia, Lejeunea 148 Centetes 93 cerea, Baetus 469 chapalanus, Cambarus (Cambarellus) 22 Characidae 453 Cheilolejeunea 149 intertexta 149 Chirotonetes ignotus 469 Chloe fuscata 469 chrysitis, Tinea 48 Chrysochloris 93 Cichlidae 456 cismontana, Rhus 189 clarki, Cambarus 24 Clupea 454 Clupeidae 454 clypeatus, Cambarus 18 Cod 68 Cololejeunea floccosa 146 goebeli 146 venusta 146 commersoni, Plecostomus 452 compacta, Eulejeunea 148 complex molars, Phyletic history of 99 tritubercular type of 99 triconodont type of 99 conjugata, Metzgeria 143 consanguinea, Metzgeria 143 consobrinus, Cambarus 12 corrupta, Sympetrum, compound eye of 459. 472 coruscans, Pseudoplatystoma 451 Cottus 69 gobio 48 Crenicichla semifasciala 457 Cretica, Pteris 151 Cribrella 127 Crossaster 130 alternatus 131 borealis 134 papposus 132 cubensis, Cambarus (Procambarus) 11 Curi matus gilberti 453 platanus 453 Cyprinus, 42 densiloba, Frullania 157 denudatum, Odontoschisma 155 Dicrocynodon 100 digueti, Cambarus (Procambarus) 21 Diller, J. S. 405 Divided Eyes of Certain Insects, Histol- ogy and Development of 459 Doris granulosus 452 Drepanolejeunea 151 setispina 157 tenuis 152 Dromotherium 98 Dryolestes 96 dugesi, Cambarus (Cambarellus) montezumae 20 duodecimspinosum, Geophagus 456 Dutton, Maj. Clarence E. 39 Echinaster 127 Echinasteridae 127 Eel 61 Eigenmann, Carl H. 451 elegantula, Rhus 195 elegantulus, Bibiocephalus, compound eye of 467 elliptica, Gymnogramme 151 Eocene Flora of Southwest Oregon 405 Ericulus 93 erinaceus, Astropecten 118 Esox 42 Eulejeunea compacta 148 euphlebia, Plagiogyria 146 Evans, Alexander W. 141 evermanni, Cambarus 18 exocellata, L,eptojeunea 151 Faxonius 24 ferox, Acestorhamphus 454 Ficus tiliaefolia 406 Fisher, Walter K. in Fishes from Buenos Aires, On a Collec- tion of 451 fiava, Lejeunea 148 flavipinnis Ilisha 455 floccosa, Cololejeunea 146 foliicola, Leptolejeunea 151 foliolata Luidia 121 fragilis, Astropecten, 120 Freyella 138 Frullania appendiculata 159 densiloba 157 makinoana 159 moniliata 159 furcata, Metzgeria 143 fuscata, Chloe 469 Fusion theory of tooth cusp development 94 Gadus 55 Geodetic Evidence of Isostasy 25 Geophagus australe 456 balzanii 456 duodecimspinosum 456 gymdogenys 456 Gidley, James Williams 91 gilberti, Curimatus 453 glabra, Rhus 175 Gobio 48 gobio, Cottus 48 goebelii, Cololejeunea 146 INDEX 489 gottschei, Braehiolejeunea 157 granulosus, Doris 452 Greene, Edward L. 167 grunniens, Aplodinotus 52 Gudgeon 68 gymdogenys, Geophagus 456 Gymnogramnie elliptica 151 hageni, Callibaetis, compound eye of 468 hamata, Metzgeria 143 Harpalejeunea 156 Harpalejeunea intermedia 154 ovata 157 pseudoneura 156 Harpioeephalus 94 Hay ford, John F. 27 helianthoides, Pycnopodia 138 Hemieentetes 93 Henri cia 127 Henricia aspera 127 polyacantha 129 Hepatica?, Notes on Japanese 141 hepsetus, Acestorhauiphus 454 Heros autochthon 456 hinei, Cambarus 18 hirtus, Bibio, Compound eye of 464 Histology and development of Divided eyes in Certain Insects 454 Hoplias malabaricus 454 hypocone 103 ignotus, Chironectes 469 Iheringichthys labrosus 452 Ilisha flavipinnis 455 inermis, Parastropecten 115 intermedia, Harpalejeunea 154 intertexta, Cheilolejeunea 149 Isostasy, Geodetic Evidence of 25 ithacensis, Rhus 178 Japanese Hepaticse, Notes on 141 japonica, Scapania 160 japonicum, Trichomanes 146 Juglans californica 406 Junius, Anax, compound eye of 463 kerguelensis, Leptyehaster 118 labrosus, Iheringichthys 452 loevis, Rhombus 59 lanceolata, Magnolia 405 laplatse, Plecostomus 452 Laurus californica 405 Leioscyphus verrucosus 144 Lejeunea cavifolia 148 flava 148 planiloba 147 Leptojeunea exocellata 151 foliicola 151 Leptolejeunea subacuta 149 Leptopty chaster 112 Leptychaster 112 Leptychaster anomalus 115 arcticus 112 kerguelensis 118 pacificus ii2 Leuciscus 42 Linckia 127 lindbergii, Metzgeria 143 Radula 145 lineatus, Archirus 458 Prochilodus 453 Lobadium 167 longula, Rhus 186 Lophius 42 I,ophius piscatorius 49 Loricaria anus 453 vi' tul a 453 Loricariida;4£2 lorioli, Ludwigia 124 Luciopimelodus pati 451 lucioperca, Perca 48 Lucius 42 ludoviciana, Rhus 183 Ludwigia bellonce 124 lorioli 124 quinaria 124 ludwigi, Luidia 122 Luidia 121 asthenosoma 124 brevispina 121 californica 121 foliolata 121 ludwigi 122 sarsi 124 Lymphatics of Scorpcrnichlhys viarmo- ratus 41 macrospila, Pimelodus clarus 452 macrothyrsa, Rhus 191 Magnolia californica 405 lanceolata 405 Makinoa 141 makinoana, Frullania 159 malabaricus, Hoplias 454 Manly, Charles M. 428 marginatus, Serrasalmo 454 maxillosus, Salminus 454 maximus, Rhombus 59 media, Rhus 188 melanostomus, Pomolobus 454 metacone 102 Metopium 167 Metzgeria conjugata 143 consanguinea 143 furcata 143 hamata 143 lindbergii 143 pubescens 143 quadriseriata 142 Mexican, Central American and Cuban Cambari 1 mexicanus, Cambarus (Procambarus) 11 moniliata, Frullania 159 montezutnoe, Cambarus 2 Cambarus (Cambarellus) 19 Mugil platanus 455 Mugilidae455 Mylia verrucosa 144 nitens, Rhus 190 Notes on Japanese Hepaticse 141 obtusidens, Leporinus 454 occidentalis, Cambarus (Cambarellus) montezumae 20 Rhus 193 Odontoschisma denudatum 155 olidus, Stolephorus 455 49° INDEX On a Collection of Fishes from Buenos Aires 451 Ophiodon 41 Orbitolites 406 oreophila, Rhus 177 ornatissimus, Astropecten 119 Ortmann, A. E. 1 ova, Harpalejeunea 157 oyamensis, Radula 144 paciricus, Leptychaster 112 Paleolagus 99 papposus, Crossaster 132 Paracambarus 1 paracone 102, 105 paradoxus, Cambarus (Paracambarus) 3 Parastropecten inermis 115 parastyle 102 pati, Luciopimelodus 451 Paurodon 101 Pediomys 99 Perca 42 lucioperca 48 petiolata, Rhus 185 Phragmicoma sandvicensis 157 Phyletic History of Complex Molars 99 Ungulate Molars 98 phyllobola, Rectolejeunea 149 Pike 61 pilosimanus Cambarus (Procambarus) 6 Pimelodus albicans 452 clarias macrospila 452 valenciennis 452 piscatorius, Lophius 49 Plagiogyria euphlebia 146 planicosta, Venericarda 406 planiloba, L,ejeunea 147 platanus, Curimatus 453 Mugil 455 Plecostomus carinatus vallanti 453 commersoni 452 laplatse 452 tietensis 453 Pleuronectes 42 Pleuronectidae 56 polyacantha, Henriciai29 Pomolobus melanostomus 454 Populus zaddachi 406 Potamogale 93 Pre-volcanic Auriferous Gravels in Cali- fornia, Age of, 405 Procambarus 2 Prochilodus lineatus 453 protocone 92, 102 protoconule 102 Protodont stage of ungulate molars 98 Protolambda 99 pseudoneura, Harpalejeunea 156 Pseudoplatystoma coruscans 451 Psilaster 114 Pteris cretica 151 Ptilidium bisseti 141 pubescens, Metzgeria 143 pulchella, Rhus 182 Pycnolejeunea tosana 153 Pycnopodia 136 helianthoides 138 Pycnopodiidae 136 pyramidata, Rhus 180 quadriseriata, Metzgeria 142 quelen, Rhamdia 452 quinaria, Ludwigia 124 Radula lindbergii 145 oyamensis 144 Raja 42 Rathbunaster 136 californicus 137 Rays 68 Rectolejeunea 149 Rectolejeunea phyllobola 149 regalis, Astropecten 121 Reptilian stage of ungulate molars 98 Rhamdia quelen 452 Rhceidium 167 Rhombus laevis 59 maximus 59 Rhus 167 Rhus, albida 194 aprica 193 arbuscula 184 arguta 192 ashei 179 asplenifolia 196 atrovirens 182 auriculata 178 borealis 188 caroliniana 181 cismontana 189 elegantula 195 glabra, a study of 167 glabra 175 ithacensis 178 longula 186 ludovicianus 183 macrothrysa 191 media 188 nitens 190 occidentalis 193 oreophila 177 petiolata 185 pulchella 182 pyramidata 180 sambucina 190 sandbergii 187 sorbifolia 195 tessellata 191 valida 185 rubidus, Astropecten 121 rutilus, Astyanax 454 Sabalites californicus 406 Salminus maxillosus 454 Salmo42 Salmon 59 sambucina, Rhus 190 sarsi, Luidia 124 sandbergii, Rhus 187 sandvicensis Phragmicoma 157 Brachiolejeunea 157 sanguinolenta, Asterias 127 scaber, Uranoscopus 49 Sciaenidae 456 Scapania 145 brevis 160 japonica 160 stephanii 160 Seorpaenichthys marmoratus, Lymphatics of 41 INDEX 49] Scotophilia 94 Scott, Prof. W. B. 451 scottii, Batrachops 457 sculpta, Sicyona 463 setispina, Drepanolejeunea 157 se»u'fasciatus, Crenicichla 457 semifasciatus, Batrachops 457 Serrasalmo marginatus 454 sexitubercular-quadritubercular stage of teeth 98 Sharks 68 shufeldti, Carabarus 24 Sicyona sculpta 463 Silurus 49 Sol aster idee 130 Solenodon 93 sorbifolia, Rhus 195 South-west Oregon, Eocene Flora of 405 Spalacotherium 98 Squalus 42 stephanii, Scapania 160 Stolephorus olidus 455 Study of Rhus glabra, A 167 Styphonia 146 Sturgeon 68 subacuta, Leptolejeunea 149 Sympetrum corrupta, compound eye of 459. 472 Talpa 93 Telacadon 103 tenuipes Blepharocera 467 tenuis, Drepanolejeunea 152 tessellata, Rhus 191 Thyopsiella 159 tietensis, Plecostomus 453 tiliaefolia, Ficus 406 Tinea 69 chrysitis 48 Tinodon 101 Tittmann, O. H. 25 Tooth-cusp Development 91 Torpedo 42 tosana, Pycnolejeunea 153 Trichomanes japonicum 146 Toxicodendron 167 tridens, Cymbarus montezumae 20 tridens, Cambarus 19 Triconodon 92 Triconodont stage of ungulate molars 98 of complex molars 99 Turritella uvasana 406 trigon 92 trigonid 92 trigonodont tooth 102 tritubercular-tuberculo sectorial 98 Tritubercular stage of ungulate molars 98 of complex molars 99 Trout 69 Tumidse 145 Ulmus californica 49 Ungulate molars, Phyletic History of, 98 Protodont stage of, 98 Reptilian stage of, 98 Triconodont stage of, 98 Tritubercular stage of, 98 Uranoscopus 49 scaber 49 uvasana, Turritella 406 valenciennis, Pimelodus 452 valida, Rhus 185 vallanti, Plecostomus carinatus 453 Venericardia planicosta 406 venusta, Cololejeunea 146 verrilli, Astropecten 121 verrucosa, Mylia 144 verrucosus, Leioscyphus 144 Vespertilio 94 vetula, Loricaria 453 whitneyi, Aralia 405 wiegmanni, Cambarus 15 cambarus (Cambarus) 15 williamsoni, Cambarus 10 yoshinagai, Acrostichum 146 zaddachi, Populus 406 Zahm, Prof. A. F. 436 WHOI Library Serials 5 WHSE 00869 3 : h.