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McGILL UNIVERSITY PAPERS FROM THE PETER REDPATH MUSEUM BIONOMICAL LEAFLETS >'><-i-:. X f CA '. f No.^ Organisms and Organization by A. WILLEY. No. 2. Alaslcan Glacier Worms (Oligochaeta) i by PAUL S. WELCH. No. 3. Scope of Biology by A. WILLEY. l-r-S-. y "ti: 4/ * 4 MONTREAL, 1917. ~r ■.Ji?^JP-S^aK?«TiafcKS,« .-v^+u^.. Bionomical Leaflets, No. 1, January, 1917. 1 "*; \. Organisms and OrRanization.— That the animal and vegetable kingdoms exhibit higher and lower grades of organiza- tion has been recognized by philosophers from the dawn of litera- ture. But exactly how these grades arc related to one another IS a problem which no ancient or modern writer has been able to solve. Explanations, which have been offered from time to time, have found acceptance in proportion as they have been based upon adequate limits of knowledge and sound intuition It IS one of the functions of morphology and clas.sification to build up, from the innumerable data secured by dissection, a certain number of types of structure which can be grasped by the human intellect. The result of continued analysis is at once to extend the lines of our science and to broaden the horizon of our Ignorance; as with Pascal's maggot which, in the small f-^v, compass of its body consists of parts incomparably smaller ■'''^* M^'^i^ ^°'."^^' y^'T '" ^^^ '^' ^'*^ '" ^^^ veins, humours in the blood, droplets in the humours, vapours in the drops, and so on until our conceptions are exhausted. It is therefore a simple matter of necessity to connect our facts of obserx'ation by some bond of principle which must be subjective, is almost certain to be ephemeral, and may be wholly artificial. There is no term in biology, involving an abstraction or a generalization, that is used in precisely the same sense by any hl";n'"''*''^'-^'''^°''--u7''^ ."''".H^ °f associations in the human brain is as impossible to duplicate as are the patterns of finger nr'" i" 1, • 'f l"' t^'^•■easpn that the 'jargon' or 'cipher-code' or technical terminology* of science has been invented, in a vain attempt to express some of the many shades of meaning ri'lLT? '"^^^ ''^"''^- "^'^^ '*• 'Th'^^ inherent ambiguitief are apt to beconie vexatious and impertinent except under the conditions of philosophical controversy. The word ' erade ' as employed in classification, meant for Aristotle and his followers a transition or promotion from a lower to a higher organization, and the various grades intervei;-ng between polyp and man constituted a series of steps or a scala naturoT Fevr ideaToi sc-u nature have been so erroneous, and few have lasted ro lone or""*""' penetrated so deeply as this. The grades exist, but you cannot pass from one to another and think you are following in the track of evolution. In our day the term 'grade' is used, with or with- out an Ideal signification, to denote a definite rank in the scheme of systematic or phylogenetic classification. See on this ooint the chapter on The Enterocala and the Ccelomocceh in Lanksster's A. WILLEY l4UifeMlW "?-*"1 ' TlSS!*"^ Zoolof^y, Part II. pp. 1-37, London (A. & C. Black), 1900. Phylogcny (phulon, race; genesis, origin) attemptR to dic?riniinate between mere gradations of type and real transition* by descent. But whatever view we may take of the relations between organisms, it is sure to be a partial one, juit as when, in the course of a single dissection, we may see many anatomical parts and very few connections. It is often an advantage to obtain a partial view of a complex field, and for this purpose we may shut out the sponges and flat- worrns, whose special characteristics are such as to merit separate consideration. With this reservation it is possible to discern, in the animal kingdom, three leading typs of organization, irre- spective of the nature of the skeletal framework, namely, the protozoic (Th. v. Siebold, 1841), the ccelenterate (R. Leuckart, 1848), and the calomate (E. H»ckcl, 1872). They are compar- able in regard to the parallel degrees of differentiation which they present in their plan of composition. In the protozoon we have a single nucleated protoplasmic unit, revealing an aston- ishing diversity of form, but reducible fundamentally to a surface layer of ectoplasm and an interior mass of more fluid endoplasm. The ccelenterate organism is furnished with a single body-cavity, the gastrovascular or primary digestive cavity (ccelenteron), circumscribed by a body wall consisting of two superposed cellular membranes: an outer protective envelope, the ectoderm, and an inner nutritive lining, the endoderm. The ccelomate •55"*o''8''*"'sm has a muscular body wall, the ectosome, and a muscular •»*>.om» splanchnic wall (splanchnon, entrail), the endosome, separated from one another by the interposition of a secondary body cavity, the coelom, which is lined throughout by a mesodermal coelomic epithelium. The ccelomate standard of organization is repre- sented in a number of morphological types, e.g., in the annelid, arthropod, molluscan, echinoderm, and vertebrate phyla or lines of descent. Within these phyla the coelom appears under various states of extension, modification, and reduction. For the justi- fication of ectosome and endosome see K. C. Schneider's Histo- logiches Praktikum der Tiere, Jena (G. Fischer), 1908. Ectosome had l)cen applied previously by W. J. Sollas [Report on the Te- tractinellida, Challenger Rep. Zool. XXV., 1888] to tho dermal layer of sponges and has been accepted by subsequent writers in this sense, but that need not interfere with its utilization here; on the contrary, it opens up an example of parallelism or con- vergence, the ectosome and choanosome (zone of flagellated chambers) of higher sponges offering a distant analogy to the ectosome and endosome of Coelomata. The terms employed above, descriptive of the twofold stratification of the body, might seem to suggest a simple evolu- tionary scries, and a novice might get the impression that ecto- plasm is alleged to have become transformed into ectoderm, and the latter into ectosome. What we have here is only one of those CnMtatton. numerous gradations of type which so often deceptively simulate a natural course of evolution. The most that ran be formulated in the interests of brevity is that in the ccelenterate phase an ectodermal epithelium is substituted for the protozoic ectoplasm. ■ \Jkum. ORGANISMS AND ORGANIZATION $ and that in the cplomate phaw a fleshy ectowme replace, a membranous ectoderm. This substitution is accompanied by an mcreasmg complication of the sensori-motor system and. in the scRmentcd invertebrates (annelids and arthropods), the ventral portion of the ectosome includes, besides the body wall, the ventral nervc-chain. In the frog the ventral ectosome com^ mSuUure'"' '"^"*a"<»"» 'ynph space and the abdominal n«K..'"//'^S simplest living coelcntcrate animal, the freshwater polyp. Hydra, the largest cells of both ectoderm and endoderm fll^mlnr" "'ifJ^ **'*'"; J^^t'-'P^scd bases into smooth, contractile filaments called muscle-processes or Kleinenl)erg's fibres, those »«"•»«»'••• of the ectoderm running lengthwise, the others around the Ixxly '"" Such cells, combining the qualities of epithelial and muscular ritments. are called cpithelio-muscular cells ('myoepithelial cells': musculo-epithel.al cells ; 'mu-scle-tail cells'). Their musrle- prcK-esses are comparable to the axial filament ('myophan axis') , f vll' '*iP'°.u"l^V.°" ?^ ^^^ ectoplasm, in the contractile stalk mnil?.|jr^' '^!i*^" animalcule. The passage from an epithelio- muscular to a dermo-muscular condition of the body wall though we cannot comprehend its modus operandi, is nevertheless suggestive and easily grasped by the imagination. Myophan ('muscle-seeming') mechanisms represent the beginnings of muscular contractility, and it is worthy of note that they exist in some Protozoa side by side with ciliary mech- anisms, as in Vorluella. which has a permanent stalk, and in fiv?ftn ^'^ V/^TP^t animalcule, which has the power of temporary M,oph.n 5^ ?u\ ''"J'*"^^ procures ,ts food by ciliary action; 5/«.tor "^•"»'*~ does that and also swims freely by the same mechanism. Mus- cular contractility, in its earliest manifestations, is thus inti- rnately bound up with the relation or reaction of the organism n vlZ'^fL'T"" V*"*"'"* "H'y ?^^'°" •'^^ °PP««'t« tendencies Hi u^ the ciha are confined to the rim of the bell-shaped body Hydra, with its sedentary habit and looping gait, has no rn^htoH.rofH' 'f^ '"'^^""u ^™°'??^* higher forms ^e find! m the order of development, that the ciliary precedes the myophan period, the latter not coinciding with the gastrula or c^lcn^S; ?irmat'e1'.SXbSS°ptse^^*" ''' establishment of the nmhlw^''^'^^^'^^' the Metazoon or multicellular animal, and dUtl%nV^ ^^^^Phy/a (multicellular plants) as well the .-.«c.n.i.. distinction between ectoplasm and endoplasm can be more or •*"•«- less clear y drawn, and, in many tissues, the ectoplasm is pr^ ?o.e^her Vh'"'"^""'"'' bridges connecting neighbouring S together. These are seen at their best in Volvox, the globe animalcule or sphere alga, whose free-swimming revofving rrmron*""""-? "• ""'"^'o"? biflagellate zooids assembled in I ccmmon mucilaginous matrix surrounding a central cavitv con- taining water. It is undecided whether Fo/im s ands LX threshold of the Metazoa as some would have it (cf RfchlJd Berlin^^r T'"'l'''^r ^i'J'^l'^iiindiger Orgar^ismus, Leipzig k Berlin (B. G. Teubner , 910, p. 502] or whether it is a downright green alga. In Prtnciples of Botany, by Joseph Y. Bergen and Bradley M. Davis, Boston (Ginn), 1906, p. 180, the authors follow Coebcl in plating Vokox umungst the Chlorophyce* or green aigae and add: "The fact that zoologists have found Vohox and its relatives of interest should not deter botanists from making use of their own." Whether or not it is better to call Vohox a flagellate infusorian or a flagellate al^a, the spherical colony is a cocnobium (kuinos, common ; bios, life) and the elementary organisms or ccenocytcs (kutos, cell) which compos it, ranging in number, in V. globator, from a minimum of 1500 to a maximum of 22,000 (A. Mtyer, Bot. Ztg., 1896). arc connected with each other by protoplasmic strands which radiate out from the circumference of each zooid. The gastrula is the didermic, the binstula the monodermic embryo of Metazoa. Vohox has, approximately, the Htructure of a blastula, i.e., a spherical ajiKreRate of cells surrounding a TMn'HiTO J^en^ral cavity. If the body of a solitary protozwm be described as uipiowm* a protosome (soma, body), the wall of the Vohox colony may be appropriately styled coenosomc, and this term could serve equally well for the wall of the blastula embryo. The gastrular and coelentcrate wall then becomes diplosome (diploos, double). The difference between Vohox and the mctazoic blastula is that the former is a polyzoic (or polyphytic) colony, i.e., a ComoMumeoenobium, whilst the latter is a multicellular embryo, i.e., a syncyctum syncytium. This distinction involves a fundamental concep- tion of the mctazoic organization — not that the individual is a colony of cleiicntary organisms, but that it is. a.H the word im- plies, an undivided whole, whose cellular structure is an incident of organization, not a manifestation of polyzoism. The syncytial theory of metazoic organization was adumbrated by J. Heitz- mann in 1873, though, as remarked by E. B. Wilson [The Cell in Development and Inheritance, 2nd edit. New York, 1900; see p. 58: The cell in relation to the multicellular body], on "insufficient evidence." It was developed as a definite theory by Adam Sedgwick during a numlwr of years (1885-1895) and received strong support and recognition from Yves DcluRe [La Conception polyroiquedesilres, R'»vucScient.,4me s^r., t.v, 1896, pp. 641-653). A. WILLEY. I'i '.•' ' McGiLL University, Montreal. Bionomital Ltttfla», McGill University, Afontreal. No. 9, February, 1917. «.n, A i?^*"" 9J^^ ? <^« (Oltgochata).*-The existence of rftther delicate, soft-bodied worms which live in the snow and ice of the glacicn of Alaaka, of the Klacien of certain high mountain!. Md perhaps in certain arctic regions, is still little known, although they were first discovered almost twenty year* ago. Recently, the imter was permitted to study a number of these " ic«-worms '^ which wore collected by Mr. W. M. Dennis, July 4, 1912, on SfS"***?"?]^" ^^'"'*^:' O'*^'" ^"V' Alaska, knd rent to Peter Redpath Museum, McGill University, Montreal. Large numben or these annelids were found in and on the snow whwh overlies theiceof the glacier and m water in the ice, remote horizontally and vertically from any other kind of environment. They proved to be partially mature specimens of Meaenchytraus solifuaut Emery, an annelid belonging to the family Enchytialdse. This species, the first " ice-worm " to be discovered was K/^VT",'fin^,S- ^"""y l'^«' A"' *!''"* R- Accad.^" riS m; «♦ w" l/"!™ "P^cra^ns collected on Malaspina GlMier, Mt. St. Elias, Alaska, as a new genus and a new species, Melanenchytrau9 8olifugus, the generic name being auggested by W"tityor ,*,^1 '^"■P""*'"' "''a'''* colour of the worms. Later J P Moore *^'" "**"• 1'99 Proc. Acad Nat. Sci, Philadelphia, pp. 125-144) repJrtJd on this species froni specimens collected on the same dacier descnbing, in addition, another species, Mes. nivus. He also fKfw K 7*'' '*y*°(. F^^'^.'M''""' Melanenchytrau8, which the latter had separated from Mesenchytraus, already established. X^^1!!!Lt» tu"'?"^"!?^ hypodermis, absence of spermathecal fn'S^ n ° *^®- *^«ft've tract, elongated sperm ducts, and the i^n^^*K"f ♦?"*"? °^ ^^^ ^°'^'^' blood-vessel. However, Moore St K • * ® P'K°!entation " although very remarkable, can ffih^H^Zn^T""/'' [!^" ^^''^. ^'^'^ «Pennathecu;do connect ,sp.,„«u,^ with the dgestive tract; that certain species of the same uenus ..."'^•"'^ fni'^-/u"*^' -^y '",**l« '^"«**' «f the sperm duct aTthafZ "'•'""• "" mtraclitellar ongin of the dorsal blood-vessel occurs in spedes of ^T^'^-^ir i'^r • '^^'^"r- L^t^' «t"dies confirm the?e KSvT^ ^^i^-^^^ defimtion of Mesenchyt n certain species somewhat recently discovered. thS fw difficulty all of the " ice-woims " knrSn 12- f^^i^l^J^^' ^- ^j^'}^^^' ""riman Alaska Expedition, 12. 59-61] studied and identified as Mes. soUfuaua, soecimens W M 1? M"\F'.-"f 'yjd on La Perouse GLierTAK Since Malaspina, Muir, La Perouse, and Grand Pacific Glaciere "-^-n Sjiv'V5 M *^' ««?«./ePon.of Alaska and some of them ^E^^an r^nH'lUififpr""'*^''* '' °°* surprising to find that the Grand Pacific Glacier specimens prove also to be Mes. solifugut. j^^. Contribution from the Entomological Uboratory. &,„,„ State Agricultural College. 6 PAUL S. WELCH The writer ['16, Trans. Am. Micr. Soc., 35: 85-1241 described a new speciea {Mes. gelidus) and a new variety {Mes. solifugus var. rainierenaia) from the snow-fields and glaciers of Mt. Rainier, Washington. Vague and indefinite reports of " worms " on the snow and ice-fields of the arctic regions and of high altitudes lead to the expectation that still other species await discovery. The unique character of the habitat of these worms is of interest. Mr. Dennis' report of " great numbers " on Grand Pacific Glacier agrees with the observations of previous collectors on the other Alaskan glaciers. Mr. J. B. Flett, who collected " ice-worms " on Mt. Rainier for the writer, found them very numerous at times. The abundance of these worms in situations Habitat which scem to preclude cecape from the ice and snow at any ■djinbmnit t™^ o^ y^*"" indicates that the adaptation to these unusual conditions must be successful. They exist in active form and multiply under freezing conditions, in a medium of ice and snow — a point of interest since it has recently been shown by experimental means that within certain limits the internal temperature of many groups of invertebrates, including Oligochaeta, approaches very closely the temperature of the surrounding medium. Only indefinite evidence concerning the food of these worms from Grand Pacific Glacier was secured, since the meager amount of material in the digestive tract in the . {)ecimens examined was composed mainly of angular, irregular, hyaline particles, appar- ently mineral in nature. In addition, there was a quantity of Food granular, organic, disorganized material which could not be identified. The writer [I. c. p. 102] found evidence that at least a part of the food of Mes. gelidus consists of the microscopic algae which occur in quantities on the snow of Mt. Rainier glaciers. Since this alga (or a similar one) occurs in some abundance on the Alaskan glaciers, it is possibly one source of food supply for Mes. solifugus. The conspicuous black coloration of the body is due to a striking abundance of pigment in the hypodermis. This pigment occurs also in the internal organs, particularly in the dorsal thickening of the pharynx, the chloragogue cells, the lymphocytes, p ^^^^_ and the spermathecae. All glacier enchytrieids known at present tion**" "* are heavily pigmented, at least in the mature stage, although this feature is not exclusively confined to the worms living in such a peculiar habitat. The seta; are small, delicate bristles, deeply set in the body- wall so that only a very small part of the length projects free from the body, which, together with the opaque, black character of the body, renders them easily overlooked. The protruding points are often broken off but when intact are sharply pointed and satM abruptly bent, while the inner ends are broadly curved in the opposite direction, the shape of the sets as a whole being lightly sigmoid, much as in the common earthworm. Setae of the stout, nearly straight form figured for Mes. solifugus by Emery ['00, The Ascent of Mount St. Elias (Alaska) by H. R. H. Prince Luigi Amedeo di Savoia, Duke of the Abruzzi, Appendix D, figs. 10 and 13] have not been observed in the preparations. The usual number of setae per bundle is 2-3, the latter being the maximum. • 'v.i:t.«K, ,„ ALASKAN GLACIER WORMS The average length of the seventeen alcoholic specimens examined is 9.3 mm., the extremes being 6.5 and 13.5 mm. sit* This length corresponds closely with that reported by Emery and Eisen but is lower than that given by Moore. Since the difference is mainly one of length rather than the number of somites (except in the more immature specimens), the state of contraction or extension at time of killing is probably responsible for the difference. The number of somites of the more mature specimens is about 53, close to that reported previously. It is interesting to note that none of the specimens from Grand Pacific Glacier shows the ruptures at the intersegmental grooves which other observers L wve described. None of the specimens shows a clitellum although sections of one approaching maturity exhibit a very slight thickening of the hypodermis on XII-XIII. Although subject to slight variation in size, typical measure- ments of the brain are as follows: length, 0.13 mm.; maximum "^^ width, 0.108 mm.; maximum thickness, 0.108 mm. In the sections examined, it is almost circular in transverse section. Some variation exists in the shape of the posterior margin from slightly convex to straight to slightly concave. Otherwise it is as previously described. Aside from the origin of the dorsal blood-vessel and the occurrence of the cardiac body, the circulatory system has not been described. Since the contents of the blood-vessels take the^^^wS" artificial stains readily and since the principal blood-vessels are rather large throughout most of their course, it has been possible to follow them out without difficulty, except for a short distance anterior to the junction of the two ventral trunks. The dorsal vessel arises from the perivisceral blood-sinus in XII. From its origin to the posterior part of V, it is large and conspicuous in sections, having a diameter of about 0.08 mm., except at the constrictions which correspond with the septa. It extends cephalad, parallel and dorsad to the digestive tract. In the posterior part of V, it suddenly decreases in diameter from about 0.052 mm. to about 0.024 mm., maintaining this dimension to I. Under the anterior part of the brain, it bifurcates, the two resulting vessels extending to the latero-ventral side of the digestive tract to form the right and left ventral trunks. They extend caudad as well-developed vessels to V where theyventrmi diminish markedly in diameter, so much so that they are very "*•*•• difficult to follow. They unite in the region of VII, formmg the ventral blood-vessel which is distinct throughout most of its course. In the vicinity of IV/V, a branch extends dorsad from each of the ventral trunks to connect with the dorsal vessel at a similar level, thus forming the one and only pair of transverse vessels. The dorsal vessel, from its origin in XII to its sudden decrease ya diameter in the posterior part of V, contains a small cardiac body. Most of the transverse sections through this region show this body to be composed of one to two distinct cells, *^**' although at intervals about five cells appear in a closely packed aggregation. The perivisceral blood-sinus appears just caudad of the origin of the dorsal vessel in XII and extends to the caudal end of the body. 8 Associated with septa IV/V, V/VI, and VI/VII, are l&rfte, gp«i loosely constructed septal glands which agree closely with Emery's figure ['00, fig. 11] of " unicellular glands," the identity of which he regarded with considerable uncertainty. The examination of the Grand Pacific Glacier material confirms the writer's previous suggestion [I.e. p. 110] that they were in reality the usual series of septal glands. Mention has already been made of the description of Mes. nivus by Moore from material collected with Mes. aolijugus on Malaspina Glacier in 1897. Although at first thinking them immature specimens of Mes. solifugua, on re-examination Moore found three lighter coloured specimens which he regarded as Identity of another species, nivus. The major character of distinction from Ma. nivus soUfugus was the different form of the spermathecse which were " much smaller than those of M. solifugua and lack the diverticula entirely; they are simple club-shaped sacs, without specially enlarged ampullae, and communicate neither with one another nor with the oesophagus." Other characters mentioned are as follows: " The epidermis about the spermathecal openings is not thickened. The male genital organs also differ; the saccus ejaculatorius is smaller, the walls of the atria less thick, and the exterr.al pore much less conspicuous. The posterior border of the supra-cesophageal ganglion is concave." W. Michaelsen ['00, Das Tierreich, 10 Lief., p. 87] suggests that nivus (" corr. nueus") is perhaps the yonng, oi solifugus. Evidence accumulated by the writer from the Grand Pacific Glacier material and from other sources virtually establishes the identity of nivus with solifugus — that nivus is an immature stage of the latter. With respect to the spermathecae, Emery found in almost mature material that all of the parts of these organs were present, save g the connection with the alimentary canal. In the immature pcrma •^^^Qaterial from Grand Pacific Glacier, the writer finds that the spermathecae are present, unite dorsad of the digestive tract in the posterior part of V and then connect with it, but lack the diverticula. Evidence is available [Welch, '14, Bull. 111. State Lab. Nat. Hist., 10: 163] that in some Enchytrffiidae, the sperm- athecae are among the last of the reproductive organs to reach maturity and that the order of development seems to be (1) development of the duct, (2) development of the ampulla, and (3) development of the diverticula. It thus seems that the spermathecae of nivus are accounted for as an undeveloped stage of solifugus. The thickened " epidermis " about the ectal open- ings of the spermathecae does not appear in the immature Grand Pacific Glacier material; likewise the penial bulb {"saccus ejaculatorius ") is smaller in the partly developed state, and the penial invagination (" external pore ") is less apparent. As to the concave posterior margin of the brain, it has already been pointed out that there is a variation from a slightly concave through the straight to the slightly convex in the same material. The lighter colour can also be explained on the grounds of im- maturity since there is evidence that the earlier stages of some " ice-worms " lack wholly or in part the conspicuous pigmentation of the adult. On these grounds the writer is convinced that nivus was described from immature stages of solifugus. Manhattan, Kansas, U.S.A. PAUL S. WELCH. Bionomical Leaflets, McGill University, Montreal 9 A'o. 3, March, 1917. i;,„,>I^!" »'?"'^ "/ Biology— li may seem difficult to assign limits to the "science of life." Life has existed from the b^ gmning of the habitable globe, "biology" from the beginning of the nineteenth century. Nor are the essentials of life in any way Identical with the essentials of biology. There are certain axioms regarded as fundamental, which have acquired sid?" preponderance in their application to problems of public health that It is found practicable to define the ground covered by biologs? ^We tS?"*.'" the definition a metaphysical explanatiS tL la Jf ^}'' "^""''^ '^^^ ^^^ «'8ns of life and assimilate the harmless and necessary prmciple of evolution, without up- setting their mental equilibrium, may consult ^vith profit Dr feplnhf Tw°R'«?''''7^\^?„r' ""'^ ^'^''^^' t^ird edition," S'.'oSl!?"'*"' Philadelphia (W. B. Saunders), 1916. One may still, on American f^i ov^? -^ twentieth century, pick up popular books in which such expressions as "blight of evolution" and "evolutionary piffle are to be found defacing the printed nage. To these sad and morbid perversions. Dr. xMcFarland's volume affords a whole- some corrective. «,o*7*^'?-*vPr''^"P'^"*'^ irritability as that property of living matter which hes at the root of all vital manifestation, t'.o autho* f^^^f^ *° "*™^ ^""^ "^ ^^^ principal vegetative tropisms, i.e.. T'S^X^v^l^^^ *°- ^""^^"^^ '*™""- The eighteen chapter^ of which the book ,8 composed deal with cell division, blcSd relationship, parasitism, infection and immunitv, graftine re- generation, and much besides. We may here focus attention upon Chapter IV. entitled "The Manifest.! E of Ufe" niE" "^r^" * *"™"'^ ^P'''^"^'' "'■ *^'^>' ^'•"'n a source of stim- ulation; the movement of attraction is called positive that of aversion, negative tropism. ' Thermotropism is the name given bv a botanist P vin Tieghem, m 1882 (Tmit6 de Bctanique. Paris, iS), to the response to thermal stimulation, or reaction to variations of Thermo^op. fh^rit /^^ Under experimental conditions it was found'"" 11 !J fi? .^^««-s?«llmgs were exposed to radiant heat, they showed their negative thermotropism by curving away from the source of heat, while Maize-seedHngs proved to be pSivelv thermotropic (J. Wortmann, Dot. Ztg. 41, 1883 Some S the effects of temperature are to be seen in the encystment of lower forms of life and m the hibernation of higher animals, hoS m naturally recurnng habits more than one tropism is involved The extreme range of temperature which any organism can en-' f^.S^r'f?"^ ^\ * minimum, ascends to its optimum of vital activity and declines towards a maximum critical point of viability be- T^ l}'^^ an increase is fatal. The spores of certain bacteria ^p-- of [vide McFarland, p. 38) can survive exposure for an hour to the*"""" temperature of hquid hydrogen (-225°C); at 25°C they reach their optimum rate of germination and division; at about ^0°C sporulation may recommence and some of these spores will sur^ Vive exposure for an hour to the temperature of boiLr wa?er 10 A. WILLEY ■Pv, ^ and even, for a few minutes, to 120°C. The corresponding data for developing trog spawTi and chick incubation, given in C. B. Davenport's Experimental Morphology, third edit. New York (Macmillan), 1908, p. 459-460, are: ^^tau Minim lun Optimum Maximum Frog spawn S'C SO'C 40''C Chick incubation 25''C 38°C 42°C Thigmotropism or thigmotaxia (thigema, a touch) is the term introduced by Max Verwom (1889) to denote response to contact or mechanical stimulation, as with the sensitive ten- drils of climbing phints. A few years later somewhat similar reactions of animals were independently classified under stereo- tropism (stereoma, a solid foundation) by J. Loeb. These terms are not mere syTionj-ms, inasmuch as stereotropism carries with it a more general connotation. Examples of thigmotropic irritability amongst plants are the leaves of the Sensitive Plant {Mimosa purf!ca)which is a wayside weed in parts of Ceylon, and the tentacles of the Sundew (Drosera rotundifolia) , a wild flower in damp parts of Canada. ThiamotroiH -pjjg protrusion of pseudopodia by Amoeba, when creeping stereotroptomon the bottom of a pond or on a glass slide, is a display of stereo- tropic activity, a very priniitive property of living 'substance, i.e., adhesion to surfaces which may or may not be associated with movements of translation upon them. But when Amoeba is touched or shaken, it tends to round up by a thigmotropic response. On the other hand, it is well known that the mo.st lu.xuriant irradiation of pseudopodia occurs when Amoeba is floating in mid-water and exhibiting, for the time being, negative stereo- tropism. Vorticella possesses a permanent stereotropic mechan- ism in its stalk; the bell has a delicate thigraotropic sensibility and a periodical pleotropic tendency. The sudden contraction to a corkscrew spiral of the stalk of Vorticella when the bell is touched or jarred is a special case of thigmotropism; the fixation by means of its contractile stalk is due to stereotropism; further- more the bell with its ciliated peristomial area (disc and peri- stome) exhibits centrifugal tendencies when, for purposes of generation or regeneration, it thrusts out an accessor}' circlet of cilia and breaks away from its stalk as a free-swimming Pieotropi.in"'"K'^"*^™- ^ appHcd the term pleotropism to the centrifugal tendencies of aquatic animals (Willey: Convergence in Evolution. London (John Murray) 1911, p. 43). The tentacles of Hydra exhibit thigmotropic response to the impact of small Crustacea, just as the tentacles of Drosera do to alighting insects, but the basal or pedal disc of Hydra is a stereotropic organ of attach- ment. chemotro^ Chemotropism or response to chemical stimulation is con- sidered under three sets of reactions; sitotropism or response to the stimulating influence of food, hydrotropism or response to the proximity of water, and oxytropism or respon.se to the pre- sence of oxygen. According to Davenport (op.cit. p 335) the earliest observations in chemotropism, based upon experiments - ( aCOPE OF BIOLOGY 11 im on p ants were recorded by C. Darwin in his Insectivorous Plants London (John Murray) 1875, and this line of experimentation was pursued with much success by W. Pfeffer (1883 et seq ) who mtroduced capillary tubes filled with solutions of certain substances (malates, etc.) into drop cultures of swarm-spores and antherozooids and thus made the discovery of chemotaxis m directrng the movemvnt of ciliated organisms. Sitotropism employed by Dr McFarland in his first edition (1910), seemi„.. ^ . to fill a gap m the terminology of vital reactions. In this con- " nection he quotes the case of caterpillais, hatched upon the trunk Of a tree, cljmbmg to the branches in order to reach the leaves upon which they feed. But the behaviour of insects is not merely tropistjc, it is also instinctive, and our author indirectly suggests that a complex instinct may be the integration of a multitude of relatively simple cell-tropisms. Sitotropic behaviour IS stiown m the orientation of the commensal sea-anemone, Adam- sia palhnta, with reference to its hermit-crab, Eupaaums pndeaun, as described by L. Faurot in his Etude mr les assoda- ttms entre les Pagures et les Actinies (Arch. zool. exp<5r. ."Sme s^r X' ^^"^•.^^^°: PI"- -*21-48G) and in J. E. Duerden'.s account of the Habits and Reactions of Crabs bearing Actinians in their claws (F. iiool. Soc, London, April, 1906). In the Adamsia-Eupagurus complex, the organisms become associated in their vouth and grow up together The young polyp, when about one centimetre »h . in height, IS found attached to stones in the regular manner, having ^d""* a cylindncal body with a broad pedal disc. As -oon as it has "'"*""" been found by its natural companion and coaxed by palpation on to the shell, the polyp places itself in a particular position with Its mouth and crown tentacles below and a little behind the mouth of the hermit crab. It then becomes deformed by wrap- ping Its pedal disc right and left around the shell until the edges jom in a suture above. The hermit crab has no need to tollow the usual cu.stom of pagurines of exchanging its shell from time to time for a larger one, because the polyp grows outwards like a mantle from the mouth of the shell forming a tube round the body of the crustacean, always keeping its mouth fixed in the same position relatively to the hermit's mouth, so that it mav receive particles of food as they are minced • bv the mouth- n??ii?fi*^ '''''*• '^\^. P^*^^' '^'^^ ^'^t"'^"^ «^ s a membrane of solidified mucus which may remain on tht ..ell as a tunnel prolonged outwards from the mouth of the shell after the polyp has been removed. When once the alliance has been fomed, I J!/I\f uF ^ ^% completely adapted to each other's ways that they behave as if they were one individual nf )i/^ ™V°P'L?' ''i,t'"?duced by C. Dai-win in 1880 (The Power of Movement m Phnts), is seen in the growth of roots w-hich some-H.d ^ . times msinuate themselves between the joints of water conZts'^""'"'" Mid block up the passage. A case in point is illustrated by G E Stone m a paper on The Clogging of Drain Tile by Roots. Torreya XI pp 51-55, J..W York, 1911. The Carolina Poplar, which « planted as a shade tree in the United States, has the habit of working Its roots through the joints of drain tiles. In the ciS 12 Ms /f . poptarrootiof Newark, N.J., in 1909, there were 15 stoppages and in 1910 there were 23 stoppages, all caused by poplar trees. In 1909, a drain pipe, 12 inches in diameter, was clogged by the roots of a pear tree in the town of Belmont, Mass. The growth originated F««r roots from a single offshoot of a pear tree seven feet away. The root, about I inch in diameter, with five annual rings, on entering the tile became subdivided into innumerable rootlets forming a matted tangle of pear roots. The mass of roots was 61 feet long; counting the separate branches gave a total of 8,498 feet or 1.61 miles. " This enormous development from a single root of a pear tree is greatly in excess of what would take place in the soil, since the conditions of the drain tile stimulate root develop- ment very materially." Heliotropism or response to the stimulation of light was, Haiiotroptam according to Professor W. Pfeffer, first .used by A. P. de Can- Phototaxi* *io'l^ ^ 1835. It is commonly exhibited by window plants under unilateral illumination. It is a very important reaction in animals and plants, occurring both positively and negatively. Photo- taxis (Verwom) might seem to be a redundant term, were it not for a certain nuance which serves to differentiate them. Moths are nocturnal Lepidoptera and therefore negatively heliotropic, avoiding sunlight. Dr. McFarland (p. 59) says: " The attrac- tive influence of a lamp upon the nocturnal insects is a striking example of positive heliotropism, many of the insects actually flying into the light to meet destruction." These insects are at once negatively heliotropic and positively phototactic. An interesting application of heliotropism in conjunction with sito- tropism has been used to account for the north-south migrations ■tioa °^ ^'""^^ ^y '^''" ^- ^- ^t^hafer On the incidence of daylight as a deter- mining factor in bird-migration (Nature, Decimber 19, 1907). The gist of the aigument is that the true north-south mignmts have been driven to seek the prolonged daylight of the northern summer in order to procure a sufficiency of food for themselves and their offspring. Incidentally it may be recalled that lighthouses are a source of great danger and disaster to birds when migrating at night: As the beacon-blaze allures The bird of passage, till he madly strikes Against it, and beats out his weary life. Tennyson: Enoch Arden. Geotropum "^^^ ^^^^ tropism which need be mentioned is geotropism or the reaction to gravity, the term being due to the botanist, A. B. Frank (1870). In seedling plants the primary shoot is negatively geotropic and the tap-root is positively geotropic. The historical sequence of terms makes it clear that the theory of tropisms is grounded in plant physiology whence it haS been extended to account for many of the reactions of animals. Migntlon A. WILLEY. ■'- i »2f<^->*«a«««&»«;'*iaa^9ifij /♦':H-' ■•-■ ,.' "1i '"^.'t-.k- -• ^ :? / v.* '\^'^ 1 ■-■J? #^ ■a, ^ .;',S '•',«»*> t^'V' l-.' »,, ,,r, 4;j •'- ,^..,i»