AL 8 The late Professor E. A. Minchin, M.A., F.R.S. Frontispiece] [See page 669 THE JOURNAL OF THE (fyukttk Microscopical Club EDITED BY A. W. SHEPPARD, F.Z.S., F.R.M.S. SECOND SERIES. VOLUME XII. 1913-1915. .»»»»--».._ ••...•••• [Published for the Club] WILLIAMS AND NORGATE, 14. Henrietta Street, Covent Garden. London, and 7, Broad Street, Oxford. PRINTED BY HAZELL, WATSON AND VIXEY, LD., LONDON' AND AYLESBURY. Ill C O N T E N T S . PART No. 72. APRIL 1913. Papers. E. Heron-Allen. F.L.S., F.R.M.S., awl A. Euiland, F.R.M.S. The Foraminifera in their Role as World- builders : A Review of the Foraminiferous Liiw stones and Other Rocks of th^ Eastern and Western Hemispheres (Plates 1-3) W. M. Bale, F.R.M.S. Notes on Some of the Discoid Diatoms . Henry Whitehead, B.Sc. Some Notes on British Freshwater Rhabdocoelida — a Group of Turbellaria (Plate 4) Charles F. Rousselet, F.R.M.S. The Rotifera of Devils Lake, with Description of a New Brachionus (Plates 5 and (3) Arthur Dendy, D.Sc, F.R.S. President's Address— By- Pro- ducts of Organic Evolution (Plate 7) . David Bryce. On Five New Species of Bdelloid Rotifera (Plates 8 and 9) ........ Notes. E. M. Nelson, F.R.M.S. A New Low-power Condenser E. M. Nelson. F.R.M.S. Xavicula rhomboides and Allied Forms E. M. Nelson, F.R.M.S. On Microscope Construction and the Side Screw Fine Adjustment (Figs. 1 and 2 in text) E. M. Nelson, F.R.M.S. Note on Pleurosiqma angukitum (Figs. 3 and 4 in text) ........ E. M. Nelson, F.R.M.S. Actinoci/clus Ralfsii and a Coloured Coma .... ..... Notices or Books ........ PAGH 1 17 4.3 57 05 83 95 90 90 98 100 101 Proceedings, etc. Proceedings from October 22nd, 1912, to February 25th, 1913, inclusive ......... Forty-seventh Annual Report, 1912 r Report of the Treasurer. 1912 . 103 113 120 PART No. 73, NOVEMBER 1913. Papers. E. Heron-Allen, F.L.S., F.G.S., F.R.M.S., and A. Earland, F.R.M.S. On some Foraminifera from the North Sea, dredged by the Fisheries Cruiser " Huxley " (International North Sea Investigations — England) (Plates 10 and 11) . 12 1 '\J ■ ■- IV CONTENTS. PACK C. D. Soar, F.L.S., F.R.M.S. Description of Arrhenurus Scour- fieldi and Acercus longitarsus, Two New Species of Water- mites (Plates 12 and 13) 130 G. T. Harris. The Collection and Preservation of the Hydroida 143 T. A. O'Donohoe. The Minute Structure of Coscinodiscus asteromphalus and of the Two Species of Pleurosigma, P. angulatum and P. balticum . . . . .155 Henry Sidebottom. Lagenae of the South-West Pacific Ocean (Supplementary Paper). (Plates 15-18) . . .101 James Murray, F.R.S.E. Gastrotricha (Plate 19) . . 211 Notes. Edward M. Nelson, F.R.M.S. On a New Method of Measuring the Magnifying Power of a Microscope . . ,239 Proceedings, etc. Proceedings from March 25th, 1913, to June 24th, 1913 . 245 Obituary Notice : Rt. Hon. Sir Ford North, F.R.S., F.R.M.S. . 258 PART No. 74. APRIL 1914. Papers. Arthur Dendy, D.Sc, F.R.S. President's Address — Organisms and Origins ........ 259 S. C. Akehurst, F.R.M.S. A Changer for Use with Sub-stage Condensers (Figs. 1 and 2) . . . . . .277 S. C. Akehurst, F.R.M.S. A Trap for Free-swimming Or- ganisms (Fig. 3) . . . . . . . . 279 E. M. Nelson, F.R.M.S. An Improved Form of Cheshire's Apertometer (Fig. 4) . . . . . . .281 F. J. Cheshire, F.R.M.S. Two Simple Apertometers for Dry Lenses (Figs. 5 and 6) ..... . 283 M. A. Ainslie, R.N.. B.A., F.R.A.S. A Variation of Cheshire's Apertometer (Figs. 7 and 8) . . . . . 287 James Burton. On the Disc-like Termination of the Flagellum of some Euglenae . . . . . . 29 J E. M. Nelson, F.R.M.S. On the Measurement of the Initial Magnifying Powers of Objectives (Fig. 9) . . . 295 S. C. Akehurst, F.R.M.S. Some Observations concerning Sub- stage Illumination (Plates 20-22) . . . .301 T. A. O'Donohoe. An Attempt to Resolve and Photograph Pinnularia nobilis ....... 309 N. E. Brown, A.L.S. Some Notes on the Structure of Diatoms (Plate 23) 317. Notes. James Burton. On a Method of Marking a Given Object for Future Reference on a Mounted Slide. . . .311 CONTENTS. V Vk v. }). M. DRAPER. A Live Box for the Observation of Insects and Similar Objects ........ 313 15. M. Draper. Dark-ground Illumination with the Greenough Binocular ......••• 313 E. M. Nelson. F.R.M.S. Amphvpleura Lindheimeri . . 315 Notices of Books ........ 339 Proceedings, etc. Proceedings from October 2Sth, 1013, to February 24th. 1914. inclusive ......... 340 Forty-eighth Annual Report, 1913 314 Report of the Treasurer, 1913 302 List of Members . ...... i — xxxii PART No. 75. NOVEMBER 1914. Papers. Edward M. Nelson. F.R.M.S. A New Object Glass by Zeiss. and a New Method of Illumination (Figs. 1-3) . . . 3 Edward M. Nelson. F.R.M.S. A New Low-power Condenser (Fig. 4) 367 Edward M. Nelsox. F.R.M.S. Binocular Microscopes (Fig. 5) . 309 A. E. Hilton. Notes on the Cultivation of Plasmodia of Badhamia utricularis (Fig. 0) ...... 381 A. A. C. Eliot Merlin, F.R.M.S. On the Minimum Visible . 385 C. F. Rousselet, F.R.M.S. Remarks on Two Species of African Volvox 393 C. F. Rousselet, F.R.M.S. Report on the Conference of Dele- gates of Corresponding Societies (British Association) held at Havre ......... 395 ( '. F. Rousselet, F.R.M.S. Pedalion ou Pedalia ; une question de nomenclature dans la classe des Rotiferes . . .397 Proceedings, etc. Additions to the Library since January 1914 . . . 399 Additions to the Club Cabinet since October 1912 ... . 401 Proceedings from March 24th to June 23rd. 1914, inclusive . 411 Obituary Notice : Dr. M. C. Cooke 422 Table for the Conversion of English and Metrical Measures . . 424 PART No. 76, APRIL 1915. Papers. R. T. Lewis. F.R.M.S. The Early History of the Quekett Microscopical Club . . . . . . 42 ~> D. J. Scourfield. F.Z.S., F.R.M.S. A New Copepod found in Water from Hollows on Tree Trunks. (Plates 24 and 25) 431 VI CONTENTS. PAGE E. A. Minchin, M.A., F.R.S. Some Details in the Anatomy of the Rat Flea (Ceratophyllus fasciatus). (Plates 26-32) . .441 Arthur Dendy, D.Sc., F.R.S. President's Address. The Bio- logical Conception of Individuality .... 465 W. Williamson, F.R.S.E., and Charles D. Soar. F.L.S., F.R.M.S. British Hydracarina : The Genus Lebertia. (Plates 33 and 34) 479 J. W. Gordon. A " New " Object Glass by Zeiss (Figs. 1 and 2) 515 G. T. Harris. Microscopical Methods in Bryological Work . 52 ! Proceedings, etc. Proceedings from October 27th, 1914, to February 23rd, 1915, inclusive . . . . . . . . .537 Forty- ninth Annual Report, 1914 . . . . . .551 Report of the Treasurer, 1914 . . . . . . 558 Obituary Notice : F. W. Millett, F.G.S., F.R.M.S. . . . 559 PART No. 77, NOVEMBER 1915. Papers. M. A. Ainslie, R.N., B.A., F.R.A.S. An Addition to the Ob- jective (Figs. 1 and 2) ..... 561 A. A. C. Eliot Merlin, F.R.M.S. Notes on Diatom Structure . 577 G. T. Harris. A Note on the Slides of Fissidentaceae in the Q.M.C. Cabinet 581 A. E. Hilton. Further Notes on the Cultivation of Plasmodia of Badhamia utricularis ...... 585 James Burton. Hydrodictyon reticulation .... 587 E. M. Nelson, F.R.M.S. Various Insect Structures . . . 593 J. W. Evans, D.Sc, LL.B. (London). The Determination of Minerals under the Microscope by means of their Optical Characters (Plates 35-37) 597 David Bryce. On Five New Species of the Genus Habrotrocha (Plates 38 and 39) 631 Notices of Books (Plate 40) ...... 643 Proceedings, etc. The Club Cabinet, Additions to . . . . .646 Proceedings from March 23rd to June 22nd, inclusive . . 653 Obituary Notice : E. A. Minchin, M.A., F.R.S. (Portrait) . 669 Index to Volume XII. . . . . . . . 673 Vll LIST OF ILLUSTRATIONS. PLATES. Portrait of the late Prof. E. A. Minchin. M.A., F.R.S., Facing page 501 1-3. Foraminiferal Limestones. 4. Rhabdocoelida. 5. Asplanchna Silvestrii Daday. 6. Rotifera. 7. Spicules of Tetraxonid Sponges. 8, 9. New Species of Bdelloid Rotifera. 10. Foraminifera from the North Sea. 11. Cornuspira diffusa Heron- Allen and Earland. Sand Grains, etc., from the Bottom Deposits. 12. <$ Arrhenurus Scour fieldi sp. nov. 13. q Acercus longitarsus sp. nov. 14. Structure of Pleurosigma bait ten m. 15-18. Lagenae of the South-West Pacific Ocean. 19. Gastrotricha. 20. View of Back Lens of Objective with P. angulatum in focus. 21, 22. Resolution with Annular Illumination. 23. Structure of Diatoms. 24, 25. Moraria arboricola sp. nov. 26-32. Anatomy of the Rat Flea. 33, 34. The Genus Lebertia. 35-37. Examination of Minerals. 38, 39. Xew Species of Habrotrocha. 40. Rhizopoda. FIGURES IN THE TEXT. Page 98. Side-screw fine adjustment. ,, 99. Upper and lower membranes in P. strigusum and P. balti- cum. „ 277. A changer for sub-stage condensers. ,, 280. A trap for free- swimming organisms. ,, 281. An improved form of Cheshire's Apertometer. ,, 285. Two simple apertometers for dry lenses. VJ11 LIST OF ILLUSTRATIONS. Page 288. A variation of Cheshire's Apertometer. -j8J. ,, ,, ,, 298. The measurement of the initial magnifying power : diagram to show relative position of apparatus. 32Q. Structure of pores in P. balticum according to O. Miiller. 365. Diagram showing method of illumination. oOO. ,, ,, ,, ,, 3C8. Centring stop-holder. 374. Diagram of eye and Ram~den disc. 383. Exhibition of plasmodia. 517. Diagram illustrating a " new " object-glass. "10' »J »? ?» »> 567. An addition to the objective : diagram. 504. Various insect structures. -3 THE JOURNAL : V OF THE <®iuhcii $$t c rose opt cal dDInIr« THE FORAMINIFERA IN THEIR ROLE AS WORLD- BUILDERS: A REVIEW OF THE FORAMINIFEROUS LIMESTONES AND OTHER ROCKS OF THE EASTERN AND WESTERN HEMISPHERES. By Edward Heron-Allen, F.L.S., F.R.M.S., axd Arthur Earland, F.R.M.S. {Read October 22nd, 1912.) Plates 1-3. " Life , as we call it, is nothing but the edge of the boundless Ocean of Existence where it comes on Soundings." — 0. W. Holmes, The Pro- fessor, V. Our late President, Prof. E. A. Minchin, F.R.S., in his last Presidential Address * dealt with certain organisms which he regarded as the simplest existing living structures, and speculated on the Origin of Life in this planet. Subsequently at the British Association Meeting at Dundee he led a most interesting dis- cussion on the same subject, a discussion which left those who had the privilege of listening to it convinced of one fact at least, viz. that no two of the eminent men who took part in the debate were agreed on any single point. But as the earliest forms of life were necessarily of such a simple nature that they could oy no possibility have been preserved as fossils, the interest of geologists may almost be said to commence with the stage in which life had become endowed with a sufficiently complex structure to leave recognisable remains in the geological record. The Foraminifera would seem to constitute such a group. Of extremely simple structure, mere protoplasm without differenti- ation other than the nucleus, they yet possess the power either of secreting a solid shell from the mineral salts absorbed from * Journ. Q.M.C., Ser. 2, Vol. XI. p. 339. Jourx. Q. M. C, Series II.— No. 72. 1 *) E. IIIRON-ALLEN AND A. EARLAND ON THE FORAMINIFERA their surrounding medium, or'of building up adventitious shells by the co-ordination of foreign material obtained from their immediate environment. These shells, from their minute size and composition, are peculiarly adapted for preservation as fossils. Hence, whatever the origin of life may have been, we might reasonably expect that among its earliest records would occur Foraminifera of simple and ancestral types, and that subsequent geological periods would show a constant progression in their development. Such, however, is not the case. So far as our geological knowledge carries us at present, the Foraminifera make their first appearance in the rocks in a highly differentiated stage, and among the earliest recognisable groups are many species- which are still existing and dominant types to-day. It is not so very many years, less than half a century in fact, since the sensational discovery of Eozoon Canadense (1) (2) (3) in the Laurentian rocks of Canada was hailed as evidence that the oldest fossil was, as might have been expected, a rhizopod. Into the long warfare which was waged round this fossil, in which the late Prof. K. Mobius took an active part (22), it is not proposed to enter in detail. But there was at the time of its discovery no greater authority on the Rhizopoda than the late Dr. W. B. Carpenter, a former President of this Club. He threw the whole weight of his authority into the scale in favour of the foramini- feral nature of Eozoon, and to the last was convinced of the soundness of his belief. But the balance of evidence has turned against him, and since his death but little interest has been shown in the question, Eozoon having been relegated by more or less general consent to the mineral kingdom. We are, however, again threatened with a renewal of the controversy, for Mr. It. Kirkpatrick, of the British Museum, has recently announced in Nature that he is in possession of fresh evidence of the foraminiferal nature of Eozoon, and will shortly publish it. The microscopical world will no doubt await this evidence with interest, not unmixed, perhaps, with some trepidation at the reopening of this chose jugee. From the point of view of the subject of our paper, viz. " The Foraminifera as World-builders," definite proof of the rhizopodal nature of Eozoon would be very welcome. Eozoon, whatever its nature may be, occurs in enormous reefs in the Laurentian rocks of IN THEIR ROLE AS WORLD-BUILDERS. 3 Canada and elsewhere, and we should thus have evidence that even at this early stage of the world's history, the Foraminifera had commenced to play that important part in the formation of strata which they have continued in nearly all the successive periods of geological history, and which is still proceeding in the deep sea to-day. It is no exaggeration to say that, in spite of their diminutive size, the Foraminifera have played, and are still playing, a greater part in building up the crust of the earth than all other organisms combined. Dismissing Eozoon for the present as incertae sedis, we find that the only other pre-Cambrian records which can be associated with Foraminifera are the peculiar bodies described by Cayeux (4) from certain quartzites and pthanites of the pre-Cambrian strata of Brittany. These are, however, of such minute size compared with other Foraminifera that their nature cannot be accepted on the evidence hitherto available. It appears, therefore, that at present we have no unquestionable records of Foraminifera in pre-Cambrian rocks ; but it is quite possible that such discoveries may be made in the future, as fossils of a higher type have been found, and it seems unlikely that Foraminifera did not, or could not, exist in seas capable of supporting such higher forms of life. When, however, we come to the Cambrian strata we find the Foraminifera flourishing, and already marked by numerous widely separated types. So long ago as 1858 Ehrenberg (5) figured some internal glauconitic casts of Foraminifera from a clay near St. Petersburg, which is known to be of Lower Cambrian age. According to Chapman (9) these casts are referable to at least five genera, viz. Verneuilina and Bolivina (family Textularidae), Nodosaria (family Lagenidae), Pidvinulina and Rotalia (family Rotalidae). Now it is noteworthy that none of these genera are of simple or primitive types, but are all comparatively complex in the arrangement of their chambers, and representing three distinct types of construction. Hence in this earliest geological record we find the group already well established, and markedly differentiated in structure. No monothalamous or primitive type appears in this earliest list, although we may be sure that they must have been in existence, both then and during antecedent ages. 4 E HERON-ALLEN AND A. EARLAND ON THE FORAMTNIFERA Since the time of Ehrenberg there have been other discoveries of Cambrian Foraminifera in America (6) (7) and Siberia (8). We have not had an opportunity of seeing either of these reports, but it may be noted that the New Brunswick rocks furnished representatives of the pelagic genera Orbulina and Globigerina (family Globigerinidae), while the Siberian rock is described as •assuming an oolitic structure on account of the numerous Fora- minifera which it contains. It is therefore apparent that the Foraminifera had already assumed that dominant position which they have ever since maintained in the biology of the sea. Turning to our own country, the oldest Foraminifera yet recorded are those described by Chapman (9) from a limestone of Upper Cambrian age near Malvern (PI. 1, fig. 1). This record is 'of great interest because all the Foraminifera described are either monothalamous (genera Lagena, SpiriUina) or polythalamous shells of simple type (genera Nodosaria, Marginulina, Cristel- laria). As will be seen from the rock section figured by Chapman, the Foraminifera of one genus, SpiriUina, form a considerable proportion of the entire mass of the rock (PI. 1, fig. 1). The other species described are stated to have been of very rare occurrence. Now SpiriUina is one of the simplest conceivable types of rhizo- podal shell structure, an undivided tube coiled on itself in one plane, iand is theoretically one of the forms which might be expected to turn up in the earliest records. Chapman has on certain minor points of structure instituted a new species {SpiriUina «Groomii Chapman) for this Cambrian type, but it appears to be nothing more than a variety of SpiriUina vivipara Ehrenberg, a species which at the present day occurs on muddy bottoms of moderate depth in all parts of the world.* So far as we are aware, however, there is no other record of its occurrence in sufficient abundance to form a noticeable constituent of any deposit, recent or fossil. In recent dredgings it cannot be described as an abundant species. In the next period, the Silurian, there are many records (10) (11) (12) (13) of Foraminifera, but they do not appear to be numerous. Brady (12) records and figures four species of the * Since this was written specimens resembling SpiriUina Groomii (Chap- man) have been found in dredgings made in Blacksod Bay, Co. Mayo, and also in the Moray Firth. They will be described and figured in the forthcoming report on the Foraminifera of the Clare Island Survey. IN THEIR ROLE AS WORLD-BUILDERS. 5> simple type Lagena, which are still existing, and of world-wide distribution. These and the Spirillina Groomii of Chapman (= S. vivipara Ehrenberg) are therefore probably the oldest living types now in existence. Of greater interest is the recording by Chapman (14) and Vine (15) of two genera of arenaceous Foraminifera, viz. Hyperam- mina and Stacheia from rocks of the Wenlock series. These constitute, so far as we are aware, the earliest evidence of the existence of arenaceous Foraminifera. The geological record does not furnish any evidence in support of the theory, so fre- quently postulated, that the earliest Foraminifera were types Avith adventitiously constructed tests \ nor do we see any reason for accepting this theory. The property of secreting mineral salts from the surrounding medium is common to organisms of all grades, whereas the power of selecting and utilising foreign material seems to indicate a later and higher stage of develop- ment. There appears to be no geological reason why the composite tests of arenaceous Foraminifera should have escaped fossilisation, when the delicate shells of -calcareous genera were preserved, had the two groups been in existence together in pre- Silurian times. The Devonian period, according to Chapman (16), presents but a single record of Foraminifera, viz. those discovered by Terquem (13) at Paffrath in the Eiffel. Chapman comments on the singular absence of Foraminifera in the Devonian seas, where the conditions for their existence appear to have been favourable. With the next period, however, the Carboniferous, the Fora- minifera first begin to justify the title of our paper as Worldr builders. Various genera make their appearance in such numbers as to form enormous deposits. In the lower Carbonif- erous strata the large arenaceous species known as Saccammina fusuliniformis (McCoy) = S. Carteri (Brady) (17) is the principal constituent of enormous areas of limestone in Great Britain and on the Continent (PI. 1, fig. 2). The upper Carboniferous limestone, on the other hand, is in most regions of the world largely built up of the shells of Fusulina, a perforate foraminifer belonging to the family Nummulinidae. Other genera which are largely concerned; in the formation of Carboniferous limestones are 'Endothyra\i^\. 1, fig. '6) and Archaediscus, while in this period 6 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA occur the first records of two genera, Amphistegi?ia and Nura- mulites, which in later times were destined to play an important part in the formation of the world's crust. The Permian and Permo-Carboniferous rocks show a decline in the importance of the Foraminifera. Perhaps it would be more correct to say that there is a falling off in the records of those large and dominant types which marked the Carboniferous period. Foraminifera of many different genera occur in the Permo-Carboniferous rocks, but they are usually of compara- tively small size, and so do not readily form a basis for rock formation. But in New South Wales and Tasmania, Nubecularia, which is the lowest type of imperforate foraminifer, forms a principal constituent of some limestones (18) (PL 1, fig. 4). TheTrias yields no strata in which Foraminifera are the principal constituent. Foraminifera occur in many horizons, but do not constitute any large proportion of the fauna. Perhaps the richest deposit is that described by Chapman (19) from Wedmore in Somerset. Similarly in the Jurassic period, the Foraminifera, although often varied and abundant, are not responsible for any important proportion of the whole bulk of the formation. They are often confined to limited zones, in which they occur in great abundance, but the species are nearly all minute and completely masked as to external appearance by other material. The most important feature of this period, however, is the sudden bursting into active existence of numerous hyaline types, principally Lagenidae, hitherto more or less unknown. They occur in the clays of the Lias of the Continent in enormous variety, passing insensibly from one species into another, and the meticulous precision of Terquem and others who have monographed these strata has embarrassed the rhizopodist with a wealth of synonyms. Up to this period the arenaceous Foraminifera have not presented any great diversity of forms, although, as we have seen, certain genera (Saccammina, Endothyra, etc.), have played an important part in building up strata. But Haeusler (20) (21) has de- scribed a most interesting series of arenaceous types from a sandy marl of Jurassic (Oxfordian) age in the Canton of Aargau (Switzerland), which includes many genera now known to us only from deep water. It is altogether one of the most pro- nounced and characteristic rhizopodal faunas recorded in the IN THEIR ROLE AS WORLD-BUILDERS. 7 fossil condition. The occurrence of this rich series of genera, some of which appear to be confined to this formation while others are hardly known except in the recent condition, suggests that the arenaceous foraminifera have, with few exceptions, always been confined to the deep sea, and that their scanty geological history may be due to that fact, and to the rarity of ancient deep- sea deposits. Passing to the Cretaceous period, we find the Neocomian and Aptian strata comparatively devoid of recognisable foraminiferal remains. But it is almost certain that Foraminifera of the smaller types existed in enormous numbers in the seas of these periods, leaving their evidence behind them in the shape of the glauconitic casts and grains which bulk so largely in the Green- sands. The Gault of England and the Continent contains a rich and varied foraminiferal fauna running into several hundred species. But although the Rhizopoda must have swarmed in the Gault seas, they do not constitute any large percentage of the total mass of the formation, and are often confined to limited zones. The same remark may be applied to the numerous beds of •chalk ranging from the Chalk Marl to the Upper Chalk. It is one of those popular beliefs which die so hard that chalk is made up entirely of the shells of the Foraminifera, and the textbooks and microscopical works abound with statements to that effect. Some of the methods suggested to students for the obtaining of specimens can only have originated in the fertile brains of the authors. The beginner is instructed to obtain a lump of chalk and scrub it to fragments with a toothbrush under water ; or to place some lumps in a bag and smash them up with a hammer, subsequently kneading the mass under a tap until the water runs away clear. It is needless to say that such methods can never produce anything but debris and disappointment. These methods, together with directions for the adequate preparation of chalk material for examination, have been fully discussed by Heron- Allen in his " Prolegomena " (23). There are very few zones in the Chalk which do not contain Foraminifera, but their number is as a rule small compared with the whole bulk of amorphous matter. But it is probable that in the Chalk sea the Foraminifera really abounded, and that the amorphous carbonate of lime is derived largely from 8 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA their comminuted and dissolved remains subsequently reprecipi- tated. Certain zones of the Chalk, notably the zones of Holaster planus and Micrdster, yield Foraruinifera in larger numbers, but even here a section of the rock will show their limited distribution^ The bulk of the organic remains will be found to consist of small spherical bodies which when cut in section show as rings (PI. 2r fig. 1). These, the so-called " Spheres " of the chalk, are perhaps- the origin of the belief that chalk is built up of the shells of Foraminifera. But whatever the " Spheres " may be, we are convinced that they are not Foraminifera. Their nature is still in doubt, although they have been relegated in turn to the Foraminifera, the Radiolaria and the Diatomaceae. Mr. W.. Hill, F.G.S., of Hitchin, whose knowledge of the microscopic structure of chalk is unrivalled, and who has devoted many years- to the study of these " Spheres," has published a scheme for the division of the Chalk into zones, based on their occurrence and numbers (32), but he is still unable to explain their origin and nature. We suggest that they may be the chitinous tests Of flagellate infusoria such as are found in great numbers in the sea to-day, of practically identical size and shape. The Chalk of Maestricht is rich in Foraminifera, and may be regarded as the starting-point of the rich Foraminiferal fauna of the Tertiary period, as it contains many large generar OrbiioliUs, Operculina, Orbitoides, etc.> which reached a maxi- mum of development and distribution in Eocene and Miocene times. Passing into Tertiary times we reach the Golden Age of the Foraminifera; the age in which they were to reach their maximum development both as regards size and abundance, and to leave their remains in great beds extending across whole continents, and often of an enormous thickness. These Tertiary Foraminifera are very sparingly represented in Great Britain. The London clay, although it contains a rich rhizopodal fauna in a limited zone, is on the whole absolutely barren, and the Thanet Sands and Woolwich and Beading beds have yielded few records. In the Bracklesham beds of Hampshire, however, we find a zone almost entirely composed of two or three species of Nummu- lites. At Selsey Bill the foreshore at low tide, on the east shore, IN THEIR ROLE AS WORLD-BUILDERS. 0 is for a large area covered with an exposure of this zone (the- 41 Park " beds), and one cannot walk without crushing vast agglomerated masses of Nummulites laevigatas, extending for miles and occupying broad areas between tide-marks. Off the extremity of Selsey Bill lies the extensive reef known as "The Mixon." It is exposed at low tide, and is then found to be a limestone principally composed of one species of fora- minifer, Alveolina Boscii Def ranee. Other species (notably a large alveoliniform Jliliolina, Nummulites, and a large Polymorphina) are to be found in the rock, but this is dominant (PL 2, fig. 2). Alveolina Boscii, which has built up enormous areas of limestone extending across Southern Europe to the Himalayas, is still in existence to-day, and is now forming similar deposits off many- tropical shores. The Selsey specimens — the only ones to be found in Great Britain — are indistinguishable from those to be dredged in shallow water to-day, off the Great Barrier Reef of Queensland and in many other places (24). At Stubbington and its neighbourhood, in Hampshire, smaller types of Nummulites, viz. Nummulites elegans and JV. variolariar are to be found in similar abundance. Turning to the Continent, we find these Nummulitic and Alveoline limestones developed to an incredible extent. With interruptions here and there, they spread in a broad band across- Europe, Asia and Northern Africa to the Himalayas, attaining in many places a thickness of several thousand feet (PI. 2, fig. 3). The species vary with the zone and locality, but, as a rule, the- whole rock is built up of their more or less perfect remains, and undeft the microscope the very debris in the interstices of perfect specimens is found to consist of their comminuted remains- (Pl. 2, fig. 4 and PI. 3, fig. 1). Among the more familiar instances of Nummulitic limestone- may be mentioned the Pyramids of Egypt, which are built of limestone quarried in the neighbouring Mokattam Hills, largely composed of a single species of Nummulite — N. Gizehensis (Ehren- berg). We illustrate in Plate 3, fig. 1 a section through a micro- spheric specimen of this Nummulite, one of a series collected for us by Mrs. A. M. King, F.R.M.S. The peculiarity of these remains struck the geographer Strabo, who accounts for their presence in the limestone by asserting that they were the petrified remains of lentils from the rations of the ancients who built the 10 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA Pyramids.* They are to this day known locally as " Pharaoh's beans." t Philip de la Harpe begins his Monograph on the genus (27) with the words, " Egypt is the classic land of the Nummulites," and Dr. Carpenter in his Introduction (28) passes in review the legends which have attached themselves to this organism, from Herodotus (?), Pliny (?) and Strabo to the learned Clusius, who refers to " the popular belief of the Transylvanians that they were pieces of money turned into stone by King Ladislaus, in order to prevent his soldiers from stopping to collect them just when they were putting the Tartars to flight ! " J Tt may be remarked that Prof. Haug has suggested (31) abolishing the Lyellian nomenclature of geological periods for all epochs later than the Cretaceous, and the redistribution of the strata into Nummulitic, Neogene, and Quaternary. He suggests that the Nummulitic, whose classification is founded solely upon this foraminifer alone, shall be divided into the Eo-Nummulitic, which will comprise the Montian, the Thanetian, and the Lon- ■donian (names which speak for themselves), the Meso-Nummu- litic, which will comprise the Lutetian and Ludian, and the Neo-Nummulitic, which includes all strata from the Lower Oligocene up to the dawn of the Glacial Period — which com- mences his Quaternary. As a rule these two dominant types, Alveolina and Nummulites, * Strabo, Geographica, lib. xvii. cap. i. §34: cpaal d'airoXidudrji'a.i \el\pava tt?s rdv epya^ofxtvocv rpocprjs. ovk direoiKe. See the note on this passage in Canon Rawlinson's translation (1860). f In spite of the fact that Herodotus (who has been credited with Strabo's observation on the Nummulites) expressly states (Euterpe, IT. § 37) that the Egyptians never grew or ate beans in any form. X Clusius (i.e. Charles de l'Ecluse, 1526-1609), in Caroli Clusii et aliorum vpistolae, Paris (Epistola xxxvii.), thus records the matter : " Intellexi item genus quoddam lapillorum planorum et quasi circino in orbem ductorum inveniri in montibus qui Pannoniam a Daciasive Transilvania disterminant, quorum alii auri, alii argenti colorem referunt et characteribus insigniti videntur sed incognitis. Ferunt Ladislaum regem quum Tartaros praeda et spoliis onustos persequeretur atque metueret, ne militum suorum avaritia ■et ignavia, qui thesauris per viam stratis ab hostibus inhaerebant, victoria illi e manibus eriperetur, a Deo petiisse ut nummi illi et pecunia ab hosti- bus in via relicta in lapides mutarentur, quo militem sic delusum alacriorem haberet in persequendo hoste." A passage contemporary with, if it should not precede, Mr. C. D. Sherborn's earliest reference to Conrad Gesner (1566). IN THEIR ROLE AS WORLD-BUILDERS. 11 do not exist together, but the transition from one dominant to the other is often quite sharp. We show a section from Sherani, on the N.W. frontier of India, illustrating the junction of the two beds. Within a thickness of two inches the rock turns from a Nummulitic to an Alveoline limestone (PI. 3, fig. 2). What possible explanation can there be for such a radical and cata- clysmic change, necessitating the practical extinction of one dominant, and the sudden rise to prominence of another, widely ■different, type? It cannot be a case of evolution, as the two species represent entirely different types of structure. With the passing of the Eocene period the Foraminifera lose their all-important position as rock-builders. Through Oligocene and Miocene times they continued to flourish, and to form •deposits largely or entirely built up of their remains. The genus -Nummulites dies out, dies so completely that at the present day it is represented by only a single small species of rare occurrence in tropical seas. Alveolina persists, but no longer as a dominant. Orbitoides, a highly specialised type which had made its first ■appearance in the Chalk of Maestricht, attains sudden abundance and forms great beds of Orbitoidal limestone in all the Con- tinents, only to die out absolutely in the Miocene (PI. 3, fig. 3). But the Miocene and later Tertiary deposits, though often presenting an abundant and extremely varied foraminiferal fauna, no longer owe their existence to the occurrence of one or iew species in enormous numbers, except in those comparatively few deep-sea deposits which have been raised to the surface in the West Indies, New Guinea and the Pacific, and which are similar in structure and often in species to the deposits which are being found in the deep sea to-day (25) (26) (PI. 3, &s-i]- . .... Perhaps the conditions under which foraminiferal life exists to-day may help to explain the change. We have now no seas -swarming with Nummulites and Alveolina, to the practical ■exclusion of other species Here and there about the world the shallow-water Foraminifera are to be found in such .profusion that, given favourable means of preservation, we should have in time a true foraminiferal limestone. From the shallow waters of the West Indian seas we have received dredgings almost entirely composed of the genera Orbiculina and Miliolina. In the shallow lagoons of the Pacific Tinoporus baculatus, Alveolina Boscii and 12 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA Orbitolites complanata still form banks which impede navigation. But speaking generally, the activity of the Foraminifera to-day is displayed in another sphere. In the surface waters of the great oceans the few genera which are found in the pelagic- condition swarm in countless numbers, and their dead shells falling constantly to the sea floor, are there building up layers of Globigerina ooze which, if solidified and raised to the surface,, would be visible as areas of foraminiferal limestone exceeding even the Nummulitic limestones in extent. Murray and Renard estimate the area of sea bottom over which Globigerina ooze is at present in process of formation at over 49 1 million square miles. Of its depth we can, of course,, form no idea, but as the great oceans are practically permanent,, it must be very great, because we know from deep-sea deposits which have been elevated into land surfaces in Malta, Barbados,. Trinidad and Australasia, that similar deposits have been forming in the deep sea ever since at least Miocene times. ■ Prof. Agassiz has observed (29) : "No lithological distinction of any value has been established between the chalk proper and the calcareous mud of the Atlantic," and it has been reasonably postulated by Prof. Jukes-Brown (30), after a careful analysis of calcareous oozes, that the chalk was deposited in a sea of less than 500 fathoms, though doubtless at a considerable distance from land. The time occupied in the deposit of the English chalk, arguing by the rate at which the Atlantic ooze is formed, which is one foot in a century, must have been 150,000 years. We cannot but feel that this paper has already overpassed the reasonable limits of such a communication, but our difficulty has been mainly one of selection. The matter is one whose ramifi- cations are almost infinite. A systematic study of the dynamics of the subject remains yet to be completed, though significant beginnings have been made by Prof. Hull and by Prof. Jukes- Brown. A careful consideration of the factors which have led to the deposition of certain forms of Foraminifera and other microzoa in an orderly sequence, dependent for the most part upon current action and specific gravity, must lead us to an understanding of the forces which have accounted for the Building of the World in the form in which we know it. And it is by the study* of such factors, as revealed by their results, IN THEIR RuLE AS WORLD-BUILDERS. 13 that geologists have been able to reconstruct the geographical features of ages inconceivably remote. Bibliography. 1. Dawson, J. W. On the Structure of Certain Organic Remains in the Laurentian Limestones of Canada. Quart. Journ. Geol. Soc, 1865, p. 51, pi. vi., vii. 2. Carpenter, W. B. Additional Note on the Structure and Affinities of Eozoon Canadense. Quart. Journ. Geol. Soc, 1865, p. 59, pi. viii., ix. 3. Ibid. On the Structure, Affinities and Geological Position of Eozoon Canadense. Intellectual Observer, No. XI., p. 278. 2 plates. 4. Cayeux, L. Sur la Presence de Restes de Foraminiferes dans les Terrains precambriens de Bretagne. Ann. Soc. Geol. Xord., 1894, vol. xxii., pp. 116-19. 5. Ehrexberg, C. G. Ueber andere massenhafte mikroskopische Lebensformen der altesten silurischen Grauwacken-Thone bei Petersburg. Sitzungs. phys.-math. Kl. Monatsb. Ak. Wiss., Berlin, 1858, p. 324, pi. i. 6. Matthew, W. D. On Phosphate Nodules from the Cambrian of Southern New Brunswick. Trans. New York Acad. Science, 1893, vol. xii., pp. 108-20 and pi. i.-iv. 7. Matthew, G. F. The Protolenus Fauna. Trans. New York Acad. Science, 1895, vol. xiv., pp. 109-11, pi. i. S. De Lapparent, A. Traite de Geologie, 4th ed., 1900, Paris, p. 790. 9. Chapman, F. Foraminifera from an Upper Cambrian Horizon in the Malverns. Quart. Journ. Geol. Soc, 1900, pp. 257-63, pi. xv. 10. Keeping, W. On some remains of Plants, Foraminifera and Annelida in the Silurian Rocks of Central Wales. Geo- logical Magazine, 1882 ; Dec. II., vol ix., p. 490. 11. Blake, J. F. Lower Silurian Foraminifera. Geological Magazine, 1876, N.S. (Dec. II.), vol. iii., p. 134. 12. Brady, H. B. Note on some Silurian Lagenae. Geological Magazine, 1888, pp. 481-84. 13. Terquem, O. Observations sur quelques fossiles des Epoques Primaires. Bull. Soc. Geol. France, Ser. 3 (1880), vol. viii., pp. 414-18, and pi. xi. 14 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA 14. Chapman, F. On some Fossils of Wenlock Age from Mulder near Klinteberg, Gotland. Ann. Mag. Nat. Hist., 1901r pp. 141-60, pi. iii. 15. Vine, G. R. Notes on the Annelida tubicola of the Wenlock Shales from the washings of Mr. G. Maw, F.G.S. Quart, Journ. Geol. Soc, vol. 32 (1882), p. 390. See also F. Chapman, Ann. Mag. Nat. Hist., 1895, Ser. VI.,. vol. xvi., p. 311. 16. Chapman, F. The Foraminifera. London, 1902, p. 255. 17. Ibid. Note on the specific name of the Saccammina of the Carboniferous Limestone. Ann. Mag. Nat. Hist., 1898, Ser. 7, vol i., pp. 216-18. 18. Chapman, F., and Howchin, W. A monograph of the Foraminifera of the Permo-Carboniferous Limestones of New South Wales. Mem. Geol. Survey, New South Wales, 1905. Palaeontology, No. 14, p. 5. 19. Chapman, F. On some Foraminifera of Rhaetic Age from Wedmore, in Somerset. Ann. Mag. Nat. Hist., 1895r Ser. 6, vol. xvi., pp. 305-29, 2 plates. 20. Haeusler, P. Die Astrorhiziden und Lituoliden der Bimammatus-zone. Neues Jahrb. filr Min., 1883, vol. i.r pp. 55-61, pi. iii., iv. 21. Ibid. Monographie der Foraminiferen der Transversarius- Zone. Abhandl. Schiveiz. Paldont. Gesellsch., 1891,, vol. xvii., pp. 1-135, 15 plates. 22. Mobius, K. Der Bau der Eozoon Canadense nach einigen Untersuchungen vergleichen mit dem Bau der Foramini- feren. Cassel, 1878. 23. Heron-Allen, E. Prolegomena towards the study of the Chalk Foraminifera. London, 1894, pp. 10-14. 24. Heron-Allen, E., and Earland, A. The Recent and Fossil Foraminifera of the Shore-sands at Selsey Bill, Sussex. Journ. R. Micr. Soc, 1908, p. 529; 1909, pp. 306, 422r 677 ; 1910, pp. 401, 693 ; 1911, pp. 298, 436. 25. Schubert, P. Die fossilen Foraminiferen der Bismarck- archipels und einiger angrenzender Inseln. K. K. Geo- logischen lieichsanstalt, vol. xx. Part 4. Vienna, 1911. 26. Jukes-Brown, A. J., and Harrison, J. B. The Geology of Barbados. Part II. The Oceanic Deposits. Quart. Joarn. Geol. Soc, 1892, vol 48, p. 170. IN THEIR ROLE AS WORLD-BUILDERS. 15 27. La Harpe, P. de. Monographie der in Aegypten und der libyschen Wiiste vorkommenden Nummuliten. Palaeonto- graphica, vol. xxx. 1883 (3 Folge, Bd. 36), p. 155. 28. Carpenter, W. B., Parker, W. K., Jones, T. B. Intro- duction to the study of the Foraminifera. London (Ray Soc), 1852, p. 262. 29. Agassiz, A. Three Cruises of the Blake. London, 1888,. vol. i., p. 150. 30. Jukes-Brown, A. J. Handbook of Physical Geology. London, 1884, p. 130. 31. Haug, E. Traitede Geologic II. Les Periodes Geologiques. Fascicule 3. Paris, 1911. 32. Jukes-Brown, A. J. The Cretaceous Bocks of Britain, with contributions by W. Hill. London, Geological Survey, volii., 1903, vol. iii., 1904. Description of Plates 1 — 3. With the exception of PI. 1, fig. 1, PI. 3, fig. 4, the figures are from original sources. Plate 1. Fig. 1. Spirillina Limestone. Upper Cambrian, Malvern (after Chapman, Q.J.G.S., vol. lvi., 1900, Plate 15). ,, 2. Saccammina Limestone. Carboniferous. Pathhead, Had- dington, N.B. ,, 3. Endothyra Limestone. Carboniferous. Indiana. „ 4. Nubecularia Limestone. Permo- carboniferous. Polkolbin, Maitland, N. S. Wales. Plate 2. Fig. 1. Middle Chalk. Zone of Rhynchonella Cuvieri. Hitchin. ,, 2. Alveolina Limestone. Eocene. Mixon Bock, Selsey. ,, 3. Alveolina Limestone. Eocene. Bunnu, N. W. Frontier India. , 4. Kummulitic Limestone. Eocene. Gizehj Egypt. 16 E. HERON-ALLEN AND A. EARLAND ON THE FORAMINIFERA. Plate 3. Fig. 1. Nummulites Gizehensis (Ehrenberg), microspheric speci- men. Horizontal section, through primordial chamber. „ 2. Alveolina and Nummulitic Limestone. Eocene. Shiranni, N. W. Frontier, India, showing the junction of the two beds. 3. Orbitoidal Limestone. Miocene. Japan. 4. Globigerina Limestone. Miocene. Bismarck Archipelago, Pacific (after Schubert, loc. cit., Plate 5, fig. 4). Jourii. Quekett MicroscopicabClub, Ser. 2, Vol. XIL, No. 72, April 1913. Journ. Q.M.C. Ser. 2, Vol. XII., PI. 1 3 4 Fo RAM IN I FERAL LIMESTONES. Journ. Q.M.C. Ser. 2, Vol. XII., PI. 2. FoRAMINIFERAL LIMESTONES. Journ. Q.M.C. Ser. 2, Vol. XIL, PL 3. 3 4 FORAMINIFERAL LIMESTONES. 17 NOTES ON SOME OF THE DISCOID DIATOMS. By W. M. Bale, F.R.M.S. (Contributed by Prof. A. Bendy, January 2Sth, 1913.) In the following notes, written for the most part several years since, I have attempted, in somewhat desultory fashion, a survey of some of the principal characters which have been utilised in the discrimination of species in three or four of the best-known genera of discoid diatoms. Some of the conclusions at which I have arrived as to the inadequacy of many of these distinctions have, I am aware, been reached by previous observers, more especially in the genus Coscinodiscus ; but in such cases the special instances now brought forward may perhaps be service- able in reinforcing those conclusions. In other cases, particularly in the genus Actinoptychus, my observations tend to prove that characters accepted as specific even by recent authors are de- monstrably unreliable. I have not pursued my investigations more fully, as I have found the subject too difficult, owing to the impossibility of procuring much of the literature, and to my total isolation from other observers. I trust, however, that these notes may not be without interest for students of the Diatomaceae, and that the suggestions therein may be of some value to those who occupy themselves with their classification. Coscinodiscus. — Notwithstanding all that has been done to- wards the elucidation of this unwieldy genus, it still remains the most difficult — as it is the most extensive — of the whole order. This follows naturally from the general similarity of form, and the absence in most cases of any specialised areas or conspicuous appendages such as serve to distinguish the species in Actin- cptychus, A uliscus, etc. Many forms which have been described as Journ. Q. M. C, Series II. — No. 72. 2 18 W. M. BALE ON SOME OF THE DISCOID DIATOMS. distinct differ only in having the markings a little smaller or larger, while others are characterised by trifling distinctions of detail which, on examination of an extended series of specimens, are found to break down utterly. On the other hand it will be seen that, in many instances, details which might be helpful in the discrimination of species have been generally overlooked. The first serious attempt to grapple with the difficulties involved in the classification of the genus was that of Grunow,. in his work on the Diatoms of Franz-Josef Land, a perusal of which leads one to regret that this acute observer did not carry out a more comprehensive survey of the whole genus. Rattray's Revision, though giving evidence of a vast amount of painstaking research, is far from final in regard to the species admitted, many of which are characterised by features obviously not of specific — sometimes not even of varietal — value. Moreover, in working over slides from well-known deposits, one finds many forms which it is impossible to place under any of the species described, though it is most unlikely that Rattray could have failed to observe them. The impression is produced that many of the descriptions have been framed on particular specimens,, without any allowance for the range of variation usually present. The "key" is minimised in value owing to the use in many of the sections of characters which are quite inconstant, or which may characterise the type but not the varieties, while the attempt to include all the sections in one key has added much to the difficulty of the undertaking, and has involved mistakes which render it in some cases quite unreliable. (As an example, let the observer take a typical valve of C. asteromphalus and attempt- to trace it through the key, and he will fail to find it. But it appears under Section 116, and, if followed backwards, it will be referred to Section 111, where the description is, "Markings rounded, granular ; interspaces hyaline, unequal, rows radial," which obviously cannot apply to the species at all.) Nevertheless Rattray's work undoubtedly represents a great advance in its suppression of a large number of pseudo-species, though one cannot but regret that the process has not been carried further. Mr. Cox, going to the opposite extreme, would reduce all the multitudinous forms of Coscinodiscus to seven species, Actinocyclus Ehrenbergii being included as one of them. Some diatomists W. M. BALE ON SOME OF THE DISCOID DIATOMS. 19 have expressed approval of this proposal, but none have adopted it, nor are any likely to do so. In surveying the various characters by which species may be defined, the outline will naturally be the first to be considered. This in the Coscinodisci, however, is of little assistance, as, except in a few aberrant species, the circular form prevails. Passing to the surface contour, we have a character which has been utilised by Grunow, Rattray, and others, but by no means so fully as might be. Thus neither of these observers, in differentiating C. asteromphalus from C. centralis, refers to the fact that the former has usually the centre depressed, while the latter is convex throughout. In several cases the absence of information on this point in Rattray's descriptions just renders the diagnosis doubtful. And this is the more important from the fact that even a good figure does not always bring out this special point. At the same time it may be observed that it is not rare for individuals of a given species to depart from the normal character in regard to surface contour, and further, that in particular localities this variation may prevail. This refers especially to a tendency for the surface to be more depressed than is normally the case, and does not apply to C oscinodiscus only. Thus in some of the Oamaru deposits we find that Aulacodiscus margaritaceus, A. amoenus and the large forms of the Triceratium favus group are all characterised by the unusually depressed surface of the valves. It may be noted, further, that it is not safe to describe the surface contour of a species without examining both valves. Rattray describes C. superbus as convex, but in reality one valve is convex, while the other has the centre depressed. Several species, such as C. tumidus, have the surface concentrically undu- lated, while in a series of forms, described by Grunow as Pseudo- Stephanodiscus, there is an asymmetrical inflation of the surface. The inflations and depressions in C. excavatus are also familiar examples of specialised areas. Variations of the radial symmetry, other than those men- tioned, are rare. A notable instance is that of C. cocconeiformis, which has the markings bilaterally arranged. In the great majority of cases the form, size and arrangement of the cellules or puncta which cover the surface are the prin- cipal or sole ground relied upon for specific distinction, many 20 W. M. BALE ON SOME OF THE DISCOID DIATOMS. so-called species being differentiated solely by slight variations in the size of the areolation, or by its increasing or decreasing in size towards the margin. All such species, unless other and weightier differences can be found, should be swept aside as spurious. The same remark applies to the presence or absence of a central area, of a central rosette of larger areolae, of bright points at the origin of the shorter radial series, of parts of the surface where the polygonal areolation is replaced by separate circular cellules, and of fine punctate secondary markings. Any of these characters may, of course, be constantly associated with a particular species; but, in many species at any rate, examination of a sufficient series readily shows that they may be indifferently present or not. Indeed, within the limits of the single species C. asteromphalus a range of forms may be found some or other of which exhibit every one of the characters just mentioned, while others show none of them. In some respects the size of the valve (i.e. with reference to the average of the species) is a determining factor in the arrangement of the markings. Thus in such forms of C. radiatus as are usually considered typical there are commonly three or four slightly larger cellules in the centre, and the rest are in distinctly radial series. In smaller valves the central cellules are no longer than the rest, and in the smallest forms the radial disposition of the cellules is totally lost. A still more striking instance is found in one of the robust forms of C. asteromphalus, common in some of the North American deposits. The largest valves have a conspicuous central rosette of large cellules, and outside these the areolae are much smaller, gradually increasing in size, however, to the mid-radius. With a diminution in the size of the valve comes a modification in the direction of levelling down the differences in size of the areolation — the rosette-cells become smaller, and those next to them larger in proportion. One stage in this series is the C. biangulatus of Schmidt, which is only a normal form of this group, and by no means of specific or even varietal value. In the smallest forms of the series all trace of the rosette is wanting, the areolae are fairly uniform in size throughout, and the centre of the valve is not depressed as in larger specimens, but convex or very slightly flattened, while in many valves the cellules are separate and circular on part of the surface, as in C. perforatus and C. apiculatus. Similarly the -I W. M. BALE ON SOME OF THE DISCOID DIATOMS. 21 C. crassus, so abundant in the Sendai deposit, simply consists of the smaller valves of the equally abundant G. borealis, to which • it bears the same relationship that C. biangulatus does to C. asteromphalus. In C. marginatus the small valves, with uniform and non- radial areolation, are considered typical, but, as in the above- mentioned species, we find that valves of maximum size have the areolation distinctly radial, with the areolae increasing in size from the central rosette towards the margin. In other species similar conditions occur, indicating that the reduction of the differences in size of the areolae is the regular concomitant of the reduction in size of the valves, and showing how little such variations are to be relied on as specific distinctions. The presence of a central area may be of specific value in some instances, but in many species it is quite worthless even as a varietal character. Sometimes its disappearance is due to the cellules surrounding it becoming enlarged at its expense. Thus in C. perforatus and C. apiculatus normal valves (if indeed wo are right in considering as normal those valves with separate round markings, which I greatly doubt) have a blank central space, and the cellules surrounding it are in no way different from the rest, but when, by the enlarging of the cellules- generally at the expense of the intervening substance, the structure becomes areolate, the most central cellules often enlarge inwards till they obliterate the area, and thus form a rosette, as in C. Oculus Iridis, etc. Far too much importance has been attached to the area in Rattray's monograph, especially in the key. The central rosette is one of the most variable of characters. In some cases, as already mentioned, it is conspicuous in the largest valves, dwindling and finally vanishing in the smaller ones ; in others, just alluded to, it results from the obliteration, entire or partial, of the central area. In some no doubt it may be regarded as a fairly constant specific character. The tendency in some species for the polygonal areolation to be replaced on a portion of the valve by isolated circular cellules may be briefly referred to. C. perforatus and C. apiculatus are familiar cases in which this modification occurs, either over the whole surface of the valve, or on more or less of one side, while 22 W. M. BALE ON .SOME OF THE DISCOID DIATOMS. in C. gigas, G. diorama, and a few others, it is the central part of the valve which is so modified. Though in C. apiculatus and C. perforat us it is universally recognised that this peculiarity is not of specific importance, the loose disposition of the markings in the central part of such species as C. diorama has been made use of to characterise the species, but in some cases at least unwarrantably. In a species found in Port Phillip the larger valves have the markings as in G. diorama, while the smaller ones are areolate throughout. When the modification in question occurs in the central part of a valve it is usually associated with a thinner condition of the silex, but this does not appear to be the case in such species as G. perforatus and G. apiculatus. In rare cases the loosely disposed and rounded markings occur on an annular area, concentric with the margin, and an interest- ing example of this is found in the large, robust form of G. Oculus Iridis found in the Mors deposit. It is a variable form as regards the surface contour, but commonly in large valves the centre and the sub-marginal zone are about equally elevated, and the inter- vening broad annular area is slightly depressed. A varietal form differs in having this depression much deeper, and, on the outer side, very abrupt, while in a third form the annular depression is very deep and narrow, and on the bottom of the depression the cellules are rounded and separate (a condition to which there is sometimes a tendency in the second form). This last variety was described by Grunow in his work on the diatoms of Franz-Josef Land as a new species, under the name of G. annidatus, notwithstanding which it was figured later on PI. 184 of Schmidt's Atlas under the name of Craspedodiscus Molleri. I have also seen a form of G. excavatus, very near to Grunow' s var. semilunaris, in which there is a complete annular depression, with round markings, not far from the centre. The circular areas of the varieties just mentioned, as well as the inflations of ordinary forms of G. excavatus, are all instances of abrupt bulging in (or out) of the substance of the valve, and in all of them the portion which is subject to this bulging appears thinner than the rest of the valve, while the markings are fainter, as well as being rounded and loosely disposed. The occurrence of " bright points " at the origin of the shorter radial series of cellules has been commonly regarded as a valid W. M. BALE ON SOME OF THE DISCOID DIATOMS. 23 specific character. In some instances these " bright points " are merely the optical expression of a local thickening of the silex ; more generally, however, they are true cellules, differing from the rest in their minute size. They are conspicuous in C. perforatus, and they form the principal ground of distinction between that species and C. apiculatus. But in examining a large series of €. perforatus var. ceilulosa I find them by no means so constant as to justify the importance attached to them. While in some valves they appear at the origin of all, or nearly all, the shorter rows of areolae, in others they are much sparser, and in a few cases I failed to detect more than four or five on the whole valve. In such cases, and when, as often happens, the central area is obsolete, it is a critical matter indeed to distinguish the valve from C. radiatus, and in passing I may note that the " C. radiatus" of my Holler's Typen-Platte is just one of these valves of C. perforatus var. ceilulosa, with all its bright points complete. C. obscurus may be mentioned as another species in which the bright points, usually present, may be either totally absent or reduced to a very small number. On the other hand the points often occur in species which are normally without them. I have met with instances of this kind in C. aster omphalus, on a narrow unilateral area where the cellules are separate and rounded. In a slide from Cambridge, Barbados, there are numerous valves of C. excavatus, most of which display these minute cellules, and in some valves not only at the origin of the radial series, but profusely interspersed among the large areolae all over the surface, even in places other than the angles of the areolae. And I have a curious valve of Endyctia oceanica, in which these minute cellules form the principal part of the areolation, the ordinary large cells only existing in scattered groups of four or five, surrounded on all sides by the network of small ones. I have referred already to the small importance to be attached •to mere differences in the size of the areolation, but I would further remark that it must by no means be assumed that only small differences are to be disregarded. Valves of C. concinnus may have only four cellules in 0*01 mm., while others may have as many as twelve, though the valve may be much larger. And I have seen a frustule of C. excentricus in which one valve was twice as finely marked as the other. Such instances show forcibly the futility of distinctions founded on the size of the areolation. 24 W. M. BALE ON SOME OF THE DISCOID DIATOMS. \ The structure of the valve-border is a feature which has not always received sufficient attention from observers, who have overlooked peculiarities which might be of service in classification. This refers to the general character of the border, and more particularly to the minute appendages which it frequently bears. The apiculi which form a circlet at the margin of many species are familiar to all observers, more especially those which in some of the Fasciculati and Cestodiscoidales attain a prominence which could not fail to attract attention. But those which are asymmetrical, and of which only one or two appear on each valve, have hitherto singularly escaped notice, except in a very few instances, where they are more conspicuous than usual. For example, in the robust form of C. lineatus, described as C. leptopus, a single larger apiculus, farther in than the rest, is quoted by Rattray as distinguishing C. leptopus from its allies. Y~et in fact it is not peculiar to this form, a similar apiculus, but more delicate, being easily discoverable in other and more nearly typical forms of C. lineatus. Further, it is equally a feature of C. excentricus, and I find it commonly present, though apparently hitherto unnoticed, in forms of that species from such different localities as Port Phillip, Cuxhaven, Santa Monica, and Peru and Bolivia guanos. (There is, of course, no justification for the line of demarcation drawn by Battray between the respective groups of the Lineati and the Excentrici. The two type species are con- nected by intermediate forms, and the same remark applies to C. excentricus and C. subtilis.) Among the Badiati the tendency is towards the production of two apiculi, which occupy positions about one-third or one-fourth of the circumference apart. They are found in many species,, though strangely enough I can find no mention of them by any observer except in the cases of G. concinnus and C. centralis, in both of which forms they are very conspicuous. Battray says that C. centralis is distinguished from C. asteromphalus by these apiculi, and cannot be united with it in the same species, as pro- posed by Grunow. An unfortunate dictum, since all, or nearly all, of the numerous varieties of C. asteromphalus agree precisely with C. centralis in this respect, while such apiculi, but more rudimentary and indefinite, are found in a wide range of forms comprised under C. marginatus, C. perforates, C. apiculatusr C. borealis and others. Their minute size and indefinite form W. M. BALE ON SOME OF THE DISCOID DIATOMS. 25- cause them to be easily overlooked against the coarsely marked background of the valve-areolation, but in C. concinnus and G. centralis they are more conspicuous, owing largely to the more delicate and transparent condition of the valve. The key to the position of these apiculi is, however, to be found in certain modifications of the valve-border which occur in the vicinity, and which indeed are often obvious when it is difficult or impossible to detect the apiculi themselves. These modifications may take the form of a thinning away of the valve-surface (C. marginatus), or an apparent notching of the margin (C. borealis, C. diorama, etc.), or a sinuation of the inner edge of the thickened border (G. aster omphalus) . In the last species this marginal structure is very conspicuous, at least in the robust valves, and it is shown in Schmidt's figures of C. biangulatus and one or two others. In C. perforatus and C. apiculatus (at least in the areolate forms) two minute notches in the extreme margin of the areo- lation can in most cases be seen, and by careful examination the apiculi may generally be found opposite them, but they appear no more than a slight thickening of the silex, wThich would certainly never be noticed except for the marginal clue. In C. marginatus the coarse radial structure of the marginal zone is thinned away over two comparatively large areas, sometimes very noticeably, but the apiculi themselves are difficult to make out. The apiculi are most fully developed in C. centralis and C. aster omiAalus. They are best seen by examining the inside of a large valve in which the marginal part is steeply convex, so that the apiculi, which project into the valve a little above the rim, can be observed without the interference of an immediate background. The apiculus takes the form of a minute disc, attached by a central point, and bearing a sub-globular or irregular mass. The border in C. asteromphalus is usually widened in- wardly so as to form an annular projection into the cavity of the frustule. The extent to which this widening takes place varies greatly, even in the same variety ; but whatever its width, so long as it projects inwards at all, it is sinuated under the apiculi, which are always uncovered, so that the sinuations are deeper as the valve-border is wider. The structure would seem to imply the presence in the living organism of some direct communicating filaments between the apiculi of the two valves, ) W. M. BALE ON SOME OF THE DISCOID DIATOMS. on which the inward extension of the border must never encroach. I have had no opportunity of proving whether this is so, or even o: ascertaining whether the apiculi of the two valves are opposite, except in a single instance — a large cylindrical frustule of C. mirificus mounted in zonal view, and in this the apiculi are opposite. In C. gigas the apiculi are, if present, obscure, and I can find no marginal indications of them. C. diorama and allied forms, however, often classed as varieties of C. gigas, have the border distinctly marked with two apparent notches as in C. perforatus. C concinnus has distinct apiculi, and many specimens have in addition crescentic processes outside the valve, partly surrounding the point at which the apiculi originate. These valves are known as Eupodiscus Jonesianus Greville (E. commutatus Grunow), but I do not think they have any claim to rank even as a variety. They are abundant in slides from Ouxhaven, mixed indis- criminately with valves having the internal apiculi only. While several forms besides those which I can identify with the foregoing species share in the peculiarity in question, there are many others in which I have failed to detect it. Such are the thick variety of C. Oculus Iridis found in the Mors deposit, also ■C. radiatus. In more typical forms of C . Oculus Iridis, however, careful search has disclosed two apiculi, which are simple bacillar projections into the cavity of the frustule. Apart from these appendages the structure of the border itself has in many cases not received sufficient attention as a help in classification. Some species have distinct borders with markings quite different from those of the valve generally, others have the areolar structure continued to the extreme margin without interruption ; in some the edge is turned over, in others it is quite flat, and frequently the specific diagnosis contains no hint of the character of the valve in this respect ; so that of two valves, differing widely in this particular, it may be impossible to decide which of them corresponds with the specific description. C. concinnus and C. centralis may serve to illustrate this. Both are very convex, but in the former the marginal part is slightly flattened, the areolae diminish to a very minute size, and are succeeded by an extremely narrow hyaline border, thinning away so as to show only a smooth single contour. In a typical C. centralis, on the other hand, the valve curves downward to the W. M. BALE ON SOME OF THE DISCOID DIATOMS. 27 extreme edge, and the areolae are of an appreciable size throughout, while the border is not thinned away, so that on focusing the margin there is visible a distinct double contour, with the walls of the last row of cellules showing as coarse transverse striae. Several species exhibit a tendency for the border to become wider in proportion as the valves are smaller. C. obscurus and V. apiculatus are instances of this. In both these species I have traced a series down to forms with wide borders, which are only to be distinguished with difficulty from C. marginatus. In Nottingham and other American deposits such forms of C apiculatus are common, and one of them figured by Schmidt (PI. 62, f. 11, 12) has been referred by Rattray to C. marginatus. In several species of the Radiati the angles of the areolae often tend to become thickened, so that in a certain focus there appears to be a bead at each angle. This feature has no specific im- portance, and I agree with Rattray that the presence at each a,ngle of a distinct spine, as occasionally found, is of no greater consequence. I have already referred to the close affinity which exists between the Excentrici and the Fasciculati, e.g. between C. ex- centricus and C. subtilis. Grunow mentioned this affinity, but Rattray says that it is remote. Grunow's view is undoubtedly correct. In a typical G. excentricus there is a central cellule, and surrounding it a circle, generally of seven. Each of these seven is the centre of an arcuate line of cellules, extending to the margin on either side, behind which is a succession of similar arcuate series, so that the whole of the cellules may be regarded as forming seven fascicles, crossing each other symmetrically, so that no division-lines exist, and for the most part each cellule will form part of three different fascicles. In C. subtilis and C. symbolophorus the number of fascicles is greater, and the divisions between them more abrupt, especially in the central part of the valve, so that the fasciculation is more manifest, but even in these forms the fascicles blend towards the margin in the same way as those of C. excentricus. I have seen a frustule of the latter species in which one valve was normal, while the other was far more finely marked, and was as distinctly fasciculate as C. subtilis. I should mention that the C. subtilis referred to is Grunow' typical form, which is quite different from Rattray's, though W. M. BALE ON SOME OF THE DISCOID DIATOMS. that observer quotes Grunovv as his authority. He describes C. subtilis as apiculate, and differentiates other species from it by the absence of apiculi. Yet Grunow says expressly that C. subtilis is non-apiculate. " Der Ausgangspunkt fiir alle diese Formen ist der stachellose C. subtilis (Ehr. partim), Gregory, Grunow " (Diat., F.-Josef Land, p. 81). This form, which is similar to C. symbolophorus, but without the stellate markings at the centre, also agrees well with Rattray's own account of Ehren- berg's original species. It is not common, and Yan Heurck figures it from guano, not finding it in European gatherings. But Peragallo, like Rattray, though claiming to follow Grunow's authority for the type, has figured and described a totally different form — an apiculate variety. Actinocyclus. — The excessive multiplication of specific names which encumbers the Coscinodisci has not been carried out to a corresponding extent in the much smaller group of the Actino- cycli (ignoring, of course, Ehrenberg's multitudinous pseudo- species) ; still there is no doubt that an undue regard for certain points of structure has led to the establishment of several species on insufficient grounds. Rattray's monograph admits about seventy species : Fome of these have no claim to recognition, but, on the other hand, I find that about fifteen out of thirty-four species or varieties which I possess cannot be identified with any of Rattray's descriptions. He has adopted in this monograph the plan of furnishing extremely long and minutely detailed descriptions, a method which renders identification more certain when one is dealing with the precise form described, but does not allow for the variations which constantly present themselves even in a single gathering. In fact, as I have remarked in reference to Coscinocliscus, many of these are not descriptions of species, but of individual diatoms. Mr. Rattray uses five places of decimals to express the fraction of a millimetre which corresponds to the diameter of a pseudo-nodule ! Of what possible use can such measurements be when applied to structures so notoriously variable ? Before discussing the range of variation in the genus, and as I shall refer repeatedly to the commonest species — A. Ehren- bergii — I must premise that I use that name in the sense in which it is used by Ralfs himself, and by Yan Heurck, Grunow, Peragallo, and, so far as I know, by all other observers except W. M. BALE ON SOME OF THE DISCOID DIATOMS. 29 Rattray, who has unaccountably assigned the name to an entirely different form, while describing the true A. Ehrenbergii as A. moniliformis Ralfs. A. Ehrenbergii was described by Ralfs from his own knowledge, while A. moniliformis was merely a name given by him to certain forms from Oran and Virginia, which he had not seen, but which he judged from Ehrenberg's tigures to be distinct, the distinction consisting in the division of A. Ehrenbergii into compartments by double lines, while A. moniliformis was divided by single ones. There is really no difference, except such as depends on the size of the valves and the number of the fasciculi. In small valves, containing few fascicles, the interfasciculate rays form a wide angle with the other series, and are therefore very marked ; and these are the " single series of dots " referred to by Ralfs. In large valves the fascicles are numerous and narrow, so the interfasciculate rays form a small angle with the other series, which, stopping short at various points, leave a double row of subulate blank spaces along the sides of each primary or interfasciculate ray, and 'these subulate areas constitute the "double lines" of Ralfs. That the small valves from Oran and Virginia, and the large ones from Cuxhaven, etc., are one and the same species is fully recognised, however, by Rattray, but he names them A. monili- formis. To any one who reads carefully Ralfs' account of A. Ehrenbergii there can be no possible doubt as to the identity of the species. It was established specially to include the many-rayed forms described by Ehrenberg, which mostly occur at Cuxhaven ; Ralfs also states that it is " very fine in Ichaboe guano," and that most of the forms can be obtained therein ; and further, that it is " common, both recent and fossil." One species, and only one, answers perfectly to this description, namely, that which Rattray calls A. moniliformis, but which, in its larger forms, at least, has been recognised by observers generally as A. Ehrenbergii. Rattray might have been justified in preferring the name of A. moniliformis on the ground of priority, but he has failed to perceive that the forms which he has placed under it are no other than the A. Ehrenbergii of authors, and has inexplicably assigned the name A. Ehrenbergii to a species (or variety) differing entirely from that described by Ralfs. It is not found at Cuxhaven, nor, so far as is known, in Europe at all ; it is far from being common, either recent 30 W. M. BALE ON SOME OF THE DISCOID DIATOMS. or fossil, and it is not found in Ichaboe guano. It is dis- tinguished from the true A. Ehrenbergii by its concentrically undulated valves, by its strong iridescence, and by its sharply defined zones of colour under low powers. Its granules are also more closely and regularly arranged, forming over the greater part of the valve a very regular areolation. To distinguish it from the true A. Ehrenbergii I propose for it the specific name of A. rex. I have only found it in the deposits of Nottingham, Curfield, Atlantic City, and Lyons Creek. Rattray's localities are necessarily unreliable, so far as they are given on the authority of other observers, of whom some at least (Ralfs, for example) were referring to the true A. Ehrenbergii, and not this form at all. Rattray's description of this species, however, requires amend- ment, especially as regards the contour of the valve. He says- that large valves have the centre depressed, and two concentric elevated zones between the centre and the border, while small valves have the centre depressed, and are convex between it and the border. This is correct so far as some of the valves are concerned, but in others the surface elevations and depressions are in the opposite order. Thus in large valves the centre is convex, and there is one elevated zone between it and the border^ Evidently the frustule is concentrically undulated as a whole, the depressions of one valve corresponding to the elevations of the other. So in the case of the small valves with depressed centre, others, evidently their counterparts, have the centre convex. Some of the valves in my slides are 0*20 mm. in diameter, Rattray's maximum being 0*17. The largest European species is, according to Rattray, A.Ralfsiir of which I have not seen specimens agreeing entirely with Peragallo's description of the type ; but among the forms of A. Ehrenbergii abundant in slides from Cuxhaven and Ichaboe guano are many which agree with that description in the arrangement of the fasciculi and subulate areas, though not in the brilliant appearance, the very large pseudo-nodule, nor the concentric arrangement of the granules. One has only to read the descriptions of Ralfs, Yan Heurck, Rattray and Peragallo to see that no two of these observers agree as to the respective characters of A. Ralfsii and A. Ehrenbergii, which is nob sur- prising if, as Peragallo states, every intermediate gradation W. M. BALE ON SOME OF THE DISCOID DIATOMS. 31 exists between the two types. This agrees with the views expressed by Grunow, Lagerstedt, and others ; it would seem, therefore, that Peragallo is justified in treating A. Ehrenbergii as at most a variety of A. Ralfsii. Most species of A.ctinocyclus have the markings arranged on the same general plan as A. Ehrenbergii. The surface of the valve is divided into cuneate areas by a number of moniliform series of granules (the interfasciculate rays), which radiate from the centre, or near it, to the marginal zone. Each cuneate area contains a fascicle of similar moniliform series, but only the central one is strictly radial, and all the others are parallel with it ; and as they all stop short of the interfasciculate rays they are necessarily shorter as they approach these rays. The great difference in the aspect of the valves dependent on the small or large number of fascicles has already been mentioned. In the largest valves, where they are most numerous, they are so narrow that they consist of very few series of granules, and the angles which they form with the interfasciculate rays are so- small that at first sight it might appear that all the series are « truly radial. Such is the structure in the largest valves of A. Ralfsii, A. Ehrenbergii, A. Barklyi, etc., but the markings are just as truly fasciculate as in the smallest form's, though the fasciculi are not so patent. No amount of variation of the kind described, therefore, is in itself of importance in classification. But great irregularities in the arrangement of the markings prevail, and there is' perhaps no other genus in which valves of one and the same species present such different aspects. While one valve may have the interfasciculate rays very distinct, all starting from a circular central ring of granules, and all the series well defined, the next may present at first sight a very different aspect, owing to the denseness of the granulation, and in yet another much of the appearance of regularity may be lost owing to its sparseness. This is especially noticeable in the centre of the valve, where there may be a regular area, with perhaps a few granules in the centre, while in other cases there may be no definite area at all. Usually the interfasciculate rays stop short at a little distance from the centre, but in the small valves of A. Ehrenbergii from Oran, as Mr. Rattray points out, they cross each other. Another point of variation is the width of the blank areas along the sides of the interfasciculate rays. 32 W. M. BALE ON SOME OF THE DISCOID DIATOMS. Jl, fasciculatus Castracane is distinguished by the notable width ■of these areas, but the character is of no specific importance. A, Ehrenbergii often exhibits such areas, and I have seen them in one valve while the other in the same frustule showed scarcely a trace of them. They may even exist on only a part ■of a valve. So far as Castracane's figures show, there is nothing to distinguish his species from A. Ehrenbergii. A frequent phenomenon in the genus is the occurrence of regular or irregular blank areas crossing the rows of puncta, •often in a sub-concentric fashion, and A. crassus is a form in which the apparent irregularity of the markings from this cause has been made a ground for specific distinction. Yet both Van Heurck and Peragallo, who admit the species, show by their figures that the markings are as in A . Ehrenbergii, except in so far as the granules ard obliterated over certain irregularly sub- concentric areas. I find nothing here to warrant the separation •of the form as a distinct species. The interfasciculate rays are also liable to interruptions, and Castracane has described a species — A. complanatus — in which they are said to be wanting, though the valve is of the ordinary fasciculate type. I greatly doubt the correctness of this, not merely on a priori grounds, but owing to Rattray's identification of this species with the form distributed by Moller as A. Ralfsii. Now the " A. Ralfsii1' of my Typen-Platte is simply one of the forms of A. Ehrenbergii in which the fasciculation is similar to that of A. Ralfsii, and which abound in Cuxhaven and Ichaboe guano material. The interfasciculate rays are certainly not wanting, though doubtless obscure and irregular in parts. Many otherwise similar valves occur in which there is no noticeable irregularity of these rays. The general aspect of the valve depends largely on the position and distance of the granules relatively to the others in the same und adjacent rows of the fascicle. In A. Barklyi the granules of each row are very close to each other, but not so close to those of the next rows ; the rows therefore remain distinct from each other even to the border. In A. Ralfsii type and var. sparsus the granules of adjacent rows are mostly side by side, so that they form straight lines crossing the fascicles, thus having as a whole a sub-concentric disposition ; they are also distinctly separated from each other. In A. Ehrenbergii there is much W. M. BALE ON SOME OF THE DISCOID DIATOMS. 33 variation, the granules often forming irregular zigzag lines crossing the fascicles; generally, however, the tendency is for the granules of adjacent series to alternate with each other, and also to be somewhat crowded, so as to form a quincuncial arrangement, which in any case prevails towards the border. In A. rex the alternate arrangement is much more pronounced, and as the granules are crowded equally all round the markings form a very regular areolation over the greater part of the valve. The appearance of the granules themselves varies remarkably in the same species. In A. Ehrenbergii some valves show them in the best focus as minute, dark, sharply defined circles, while in others they are more pearly, and show, much more readily, a central black spot. When crowded, especially towards the border, they form a distinct areolation. In A. rex the latter type predominates, but near the centre the granules are more pearly. In A. Barklyi and A. ellipticus they vary much as in A. Ehrenbergii. And in all these species they appear some- times as dark, well-defined puncta. Peragallo has figured a form which he calls A. nebulosus, and which is practically a hyaline valve of A. Ehrenbergii with fine puncta instead of granules, also a corresponding form with the puncta arranged like the granules of a typical A. Ralfsii. He thinks these valves are probably the result of cleavage, of the correctness of which opinion I think there can be no doubt. Corresponding forms of A. Barklyi are found in hundreds in slides of that species, often so delicate and colourless that they become invisible on a slight alteration of the focus. How many layers has a valve of A. Barklyi% When manipulating one under the microscope I saw it divide into three, one extremely thin and hyaline, and another somewhat thicker, but still less robust than the main disc. Here the question of colour comes in for consideration, for it is probable that the colour as well as the appearance of the granules depends more or less on the " state " of the valve — whether it consists of more than one plate for instance, or whether the two plates include a film of air between them. A. rex is the most brightly coloured form I have seen, having the colours in sharply defined zones. A. Ehrenbergii is usually blue, green, purple, or brown, often showing more than one colour, but not in sharp zones. A . Barklyi varies much in the same way, but is exceptionally liable Journ. Q. M. 0., Series II.— No. 72. 3 34 W. M. BALE ON SOME OF THE DISCOID DIATOMS. to exhibit a dark, semi-opaque aspect. But all these species usually include forms of the same size, contour and arrangement of markings, but of a soft brown colour, uniform throughout or nearly so, and generally with fine punct'a. Are these complete valves, or secondary plates, or primary plates from which the secondary ones have been detached ? Some of these brown discs have the silex of the subulate areas so thickened as to appear black under a low power. Valves of A. Ehrenbergii with sharply defined granules and clear, distinct subulate areas mostly appear blue under low powers, with the subulate spaces white. Others, such as that described above, from Holler's Typen-Platte, are more commonly green or purple, and show no white streaks, though having large subulate areas, the substance of the valve itself appearing to have a dusky tint. The bright colours of these species can only be seen when dry or mounted in balsam or a similar medium, while in water they are colourless. No other diatom known to me presents such endless variety of marking as A. Barklyi, and occurring, as it does, in such profusion, it is especially suitable for a study in variation. This diatom is of interest as being probably the first to be named in Australia, it having been described by Dr. Coates in the Trans- actions of the Royal Society of A^ictoria for 1 860, under its present name. Rattray incomprehensibly calls it " Actinocyclus Barklyi (Ehr.) Grun.," though he knew that it was named by Coates, and not by either of the authors cited. He quotes a reference to it in the Q. J. M. S. for 1861 (wrongly quoted as "Plate CXXXVIII." instead of "Page 138 "), but does not refer to Coates' original description. It is distributed by Moller under the name A. dubius Grunow. It is one of the largest of the genus (perhaps the largest), specimens in my slides attaining a diameter of 0*24 mm., or more than double the maximum size assigned to it by Rattray. In normal valves the fasciculi are arranged much as in A. Ralfsii, but great variety exists in the denseness or otherwise of the granules, which, as in A. Ehrenbergii, also vary greatly in sharpness. But it is in individual departures from the normal arrangement that the tendency to variation exhibits itself in such an extraordinary degree. In many cases the markings are interrupted at a uniform distance from the centre, so as to form a ring, and several such concentric rings may exist on one valve, W. M. BALE ON SOME OF THE DISCOID DIATOMS. 35 dividing it into zones. Sometimes the markings are denser on one of these zones than elsewhere. Very often the zones form hyaline bands on which the granules are wanting, and the structure may be further complicated by the addition of radial hyaline bands, e.g. two hyaline zones may be joined by a number of equidistant radial hyaline areas so that the space between them is divided into a circular series of sub-rectangular com- partments ; or a broad circular zone may be filled with hyaline patches of all sorts of irregular shapes. The radial series of granules may be all curved in a spiral fashion (a variation which also occurs in C. Ehrenbergii), and I have specimens in which the central portion, as far as the first circular interruption, has the moniliform series all contorted in the most extraordinary manner. As in A. rex, etc., the subulate areas may be either darker or lighter than the rest of the valve. There may be a small central area, or the whole centre of the valve may be sparsely and irregularly marked. I find that in some slides concave and convex valves are mixed about equally, leading to the conclusion that the two forms represent opposite valves, as in A. rex, but in other gatherings I find many concave valves to every convex one. Rattray de- scribes the valves as flat in the centre and otherwise convex, but in numerous cases the convexity (or concavity) is uniform throughout. Asteromphahis. — In this genus the lines which radiate from about the head of the centro-lateral area to the apices of the areolate compartments have been assigned too much value in classification. Whether they originate from a single point, or whether they bifurcate, is absolutely immaterial, and the presence of geniculate bends in their course is, in some species at least, equally unimportant. A. Hookeri, which is not rare in one of the "Challenger" Antarctic soundings, illustrates this. The forms with six, seven, eight and nine rays, which represent four of Ehrenberg's "species," also a ten-rayed form, occur in slides which I have prepared from this material, and 1 find the geniculations of the radial lines very marked in some valves, while others show no trace of them ; others again exhibit a mixed condition. A good deal seems to depend on the size of the valve, the geniculate lines being most common in the smaller ones. Certain species are subject to variation in the outline. A. Cleveanus, as figured by Schmidt, has a rather narrow ovate 36 W. M. BALE ON SOME OF THE DISCOID DIATOMS. form, but in mud from Manila it has a broader outline, and I found one valve perfectly circular. Actinoptychus. — This genus is distinguished by its valves being divided into six or more radial cuneate compartments, which are alternately raised and depressed, the markings also differing (in normal valves) on the elevated and depressed areas. On what we may call, for want of a better term, the primary areas {Hauptfelder of Schmidt), the coarse markings are usually more robust, and often of different form, from those on the secondary areas (Nebenf elder of Schmidt) ; further, the primary areas usually bear a tooth or process near the margin, with, in some species, a radial line connecting it with the umbilicus ; while the secondary areas sometimes terminate in a submarginal hyaline band, which is not found in the primaries. The fine striation also is commonly different on the two sets of compartments. The striation is generally fairly uniform within the limits of a species, but the secondary markings, consisting of hexagonal or irregular reticulation, or systems of branching veins, is most variable in its distinctness, and is often wanting. When this occurs it is generally assumed to be the result of the detachment of the separate layer of the valve which is thus marked, but in view of the fact that different valves exhibit every possible degree of obsolescence of these markings, I have no doubt that in many cases they have not been developed. Among the characteristics to which too much importance has been attached in classification are — the number of areas, the substitution of primary for secondary areas (so that all the areas are alike), the presence or absence of the secondary markings, also of the lines connecting the umbilicus with the processes, and the presence of small variations in the striation. The adoption of these purely artificial distinctions has led not only to the undue multiplication of specific names, but, what is worse, to the lumping together of forms which are by no means closely related. In several species there are six areas, a number which is rarely, if ever, departed from. Such are the forms composing the group of which A. boliviensis is typical. In the majority of species there is no constant number; for example the beautiful A. Heliopelta, valves of which usually have six, eight, ten, or twelve areas (constituting Ehrenberg's four species of Heliopelta), while more rarely there are fourteen or sixteen. A. undulatus, W. M. BALE ON SOME OF THE DISCOID DIATOMS. 37 the most widely distributed species, is found in most localities with six areas only, yet in some Calif ornian deposits it occurs freely with up to eighteen areas, possibly more. A. undulatus is a species which well illustrates the tendency of the genus to vary in several directions, but the variations are so numerous and so closely linked, and their relationships so obvious, that they have not been made the basis of so many pseudo-species as might have been expected. I have noted about twenty-five forms sufficiently distinct to admit of their being separated for convenience of cataloguing, but few of them are so characteristic as to constitute definite varieties. In forms of average size, which may be considered fairly typical, the secondary markings are commonly about four in O'Ol mm., while in the var. microsticta of Grunow, there may be about seven, and in large forms like forma maxima Schmidt, there are only one and a half to two. The reticulation may be either hexagonal or irregular, robust or faint, and sometimes entirely wanting. The sub-marginal processes are said to be sometimes absent ; in fact, both W. Smith and Yan Heurck appear to regard this condition as typical, but I have not seen specimens without some trace of them. (The obsolete genus Omphalopelta comprised the valves with processes.) The processes may be very small, appearing merely as a slight thickening of the border, or may be placed a little farther in, presenting a somewhat irregular keyhole-shaped aspect. In many forms the secondary areas have on their margin a small hyaline patch in the corresponding position to that occupied by the processes in the primaries. On both sets of areas the outermost portion, immediately adjoining the margin proper, usually bears radial lines, being continuations of the boundaries of the last row of secondary markings, which, like the secondary markings generally, are most robust on the primary areas. The rim may be smooth, or may have few or many minute apiculi scattered over it. The puncta which compose the striae of the primary areas are arranged in quincunx, so that the striation is the same as in Pleurosigma angulatum, but those of the secondary areas form two sets of diagonal striae cutting each other at right angles, as in P. formosum. Schmidt describes as A. biformis valves in which these two sets of striae meet at rather less than a right angle, so that a third set is visible, closer than the other two, and crossing the area transversely. 38 W. M. BALE ON SOME OF THE DISCOID DIATOMS. Some valves which I have seen with this character were in all other respects similar to normal valves of A. undulatus, among which they occurred, and I see nothing to justify their separation, the slight divergence from the rectangular arrangement of the striae being no more than is often found in P. formosum. Some- times the striae meet at more than a right angle, so that the third set is radial instead of tangential. If Schmidt's species were accepted, this should make another species ! The striae are sometimes nearly or quite obliterated on small patches at the outer angles of the secondary areas, and occasionally along the margins ; in some forms again they are wanting or represented only by a few scattered puncta on a great part of those areas. The umbilicus varies greatly in size, and may be either hexagonal or may have three concave sides. Much variation exists in the extent to which the areas are inflated, or, in other- words, in the depth of the undulations. A consideration of the variations of this diatom will show how many features there are which, met with in isolated forms, may lead to the undue multiplication of species. In several species, perhaps in the genus generally, there is a tendency to produce valves in which the secondary areas or " Nebenfelder " are replaced by primary ones or " Hauptfelder," so that all the areas become alike, except in their elevated or depressed condition. Van Heurck has figured such a form of A. undulatus — the forma sexapjiendicidata, which he says may co-exist in the same frustule with the normal form. He refers only to the presence of a process on every area, and does not mention that the areas are otherwise modified, which, however, I have always found to be the case. Other varieties of A. undulatus exhibit the same tendency ; thus the large forma maxima found in the Nottingham deposit is accompanied by its "forma sexappendiculata" as also is an equally large variety which only differs from it in the strongly apiculate margin. In all these cases the compartments all correspond exactly with the normal primary areas, both in the striation and the coarser secondary markings. There may possibly be varieties with this as the usual condition, as I have found one or two such forms sparsely distributed in material where I noticed no typical valves to which they might correspond. In A. Heliopelta also valves are formed in which all the areas are alike, instead of alternately primary and secondary. It is to be noted that in all species where this phenomenon W. M. BALE ON SOME OF THE DISCOID DIATOMS. 39 occurs it is always the primary area, with its process, which is duplicated ; we never see valves with all the areas alike and having the distinctive markings of the secondary ones. Notwithstanding that it has been recognised that in A. undu- latus the variation in question has no specific importance, being found, in fact, in frustules otherwise normal, a parallel variation in other cases has been made a ground for the foundation of new species, even by observers as recent as Grunow and Schmidt. Such instances are A. Janischii Grun., which, as I shall demonstrate, is only a state of A. splendens, and A. Molleri Grun., which is a form of A. adriaticus Grun. Van Heurck says of A. Janischii that it " se distingue de toutes les autres especes du genre en ce que la valve a toute juste moitie autant d'ondulations que de divisions, de facon qu'une elevation n'est suivie d'une autre elevation que pres da deuxieme appendice suivant. Une espece analogue mais plus petite est V A. Jfolleri d'Adelaide, qui se distingue en outre par sa structure plus delicate et l'absence d'une ligne mediane." This is simply equivalent to saying that each area, instead of each alternate area, bears a process, and it is surprising that the writer did not observe that the character referred to as so exceptional was no other than he has figured in the same plate in the forma sexappendicidata of A. undulatus. A. glabratus Grunow and A. Janischii Grunow are, in part at least, forms of A. splendens, but there is a difference in the relationship which they bear to that species, A. glabratus simply consisting of valves wanting the secondary markings, while A. Janischii is an internal disc. A. splendens commonly has a distinct secondary layer showing more or less branching venation, with the typical distinction between primary and secondary areas, but a gathering usually includes a propor- tion of valves in which the secondary layer is wanting ; and although there is every possible gradation, the smooth valves have been described as a doubtful species, under the name of A . glabratus. Also accompanying them are valves in which all the compartments bear processes, and to these the name A. Janischii has been given, Janisch having figured one of them (as Halionyx vicenarius) in his paper on diatoms from guano. Tn Peru guano A. splendens is one of the commonest species, and the typical valves, with their glabratus-iovms and Janischii-iovms, are readily obtained. In a Cuxhaven gathering I also find all three forms together. And in a slide of Thum's, 40 W. M. BALE ON SOME OF THE DISCOID DIATOMS. which contains a very robust variety, all three forms are similarly associated. In the valves described as A. Janischii the marginal sculpture differs somewhat from that proper to A. splendens, but this is a necessary concomitant of the substi- tution of primary for secondary areas. In A. splendens, as in several other species, the secondary areas terminate in a sub- marginal hyaline band, which encroaches slightly on the primary areas at each side of it. When, however, all the areas have the same structure, this band is wanting, all except the small portion which properly belongs to the primary areas, so that a small rounded hyaline patch opposite the edges of the compartments is all that remains. The relationship between these forms has always appeared to me obvious, as it evidently did to Ralfs, who describes A. splendens as having a tooth on each compartment, or sometimes only on alternate compartments. In order to obtain actual proof of this, however, it occurred to me to examine some Peru guano cleanings which had furnished numerous slides, but in which the complete frustules of A, splendens, where they occurred, had been left. I picked out ten of these and mounted them in balsam, with the result that I found that three out of the ten contained valves of the so-called A. Janischii, each being included in a frustule between two of the normal valves. In all cases where I have examined whole frustules of A. splendens I have found that the two valves were either alike in the number of areas, or one valve had a pair more than the other. Thus, if one valve had sixteen areas it could be predicated that the other would have fourteen, sixteen or eighteen. Where an internal disc was found (A . Janischii) it had the same number of areas as one of the outer valves. In the slide referred to one frustule had the outer valves with fourteen and sixteen areas respectively, and the internal disc with sixteen ; another had the outer valves with sixteen and eighteen, and the inner with eighteen ; and the third had twenty throughout. The areas of the inner disc have the processes rather smaller than those of the outer valves, and nearer the margin. Though the inner disc is usually smooth, like the so-called A. glabratus, this is not invariably the case. I have a specimen covered with reticulations as distinct as in the typical valves. In Van Heurck's opinion several genera, as well as species, have been founded on mere internal valves of various species of Actinoptychus (as also of Asterolampra). Such are Debya and W. M. BALE ON SOME OF THE DISCOID DIATOMS. 41 Gyroptychus, Debya being an internal disc of A. undidatus, very unlike the outer valves, and found by Van Heurck inside the normal frustules. The A. jjellucidus Grunow, figured in Van Heurck's synopsis, PI. 123, fig. 1, is, as will be obvious to any one who compares it with the figure of A. Heliopelta in the same plate, merely a valve of the latter with the border wanting and the secondary reticulation undeveloped. In a genus-slide by Thum I have several such valves, but for the most part they retain a little more of the border, showing the origin of the spines, and some of them also have the secondary markings more or less distinctly indicated. In many marine gatherings from Port Phillip a form of A. adriaticus is found in great profusion, of which a specimen is figured in Schmidt's Atlas, PI. 153, fig. 14. It varies greatly in the distinctness or otherwise of the secondary markings, and especially in the presence or absence or fragmentary condition of the narrow radial lines which in the typical A. adriaticus, as in A . splendens, run outward from the umbilicus, or near it, to the processes. In most slides a few specimens may be found with all the areas alike, and a process on each, and it is this form which has received the name of A. Molleri Grunow. Normally the areas are arched at the ends, as shown in Van Heurck's figures, the secondary ones being shorter than the primary, with a wide hyaline band outside them, but as in the form called A. Molleri they are all primary areas, and conse- quently of the same length, the hyaline band is reduced to a small triangular area at the junction of every two compartments with the margin. All the variations of marking which occur in the normal valves are found equally in this form, and their specific identity is obvious. In reality, this so-called A. Molleri is the true A. adriaticus described by Grunow, his original figure showing a valve with processes on all the areas, and exactly the same marginal sculpture as described above. It is true A. Molleri is supposed to be without the radial lines to the processes, but Grunow recognised in his original description of A. adriaticus that these lines might be present or not, in which he was certainly correct. These radial lines, however (sometimes called pseudo-raphes), appear to be considered by Van Heurck as distinguishing A. adriaticus from A. vulgaris, though he admits a possible exception in A. adriaticus var. pumila. In the common Australian form, however, it is obvious that the presence of 42 W. M. BALE ON SOME OF THE DISCOID DIATOMS. these lines has no specific or varietal significance whatever. Almost every gathering shows valves both with and without them, and innumerable specimens exhibit an intermediate con- dition, i.e. where the lines are more or less broken, or where they are present on some of the primary areas of a valve and not on others. They are scarcely ever complete, but generally stop short of the umbilicus, as in the var. balearica. Valves without them are otherwise identical with those possessing them, having exactly the same range of variation in other respects, and this applies equally to the so-called A. JIdlleri. While reliance on such characters as the foregoing leads to the improper separation of allied forms on the one hand, it tends in other cases to the opposite error. Thus several varieties of A. glabratus have been described, and while some are, as before- mentioned, only smooth valves of A. splendeiis, there are others which, so far as I know, cannot be identified with any special form of that species, and which may probably be themselves entitled to specific rank. A. vulgaris also, as generally under- stood, includes forms which have really no close relationship. One such form is nothing but A. undulatus^ as it is found in Redondo Beach and other deposits, with mostly fourteen areas. The deposit mentioned contains numerous valves of the ordinary form, with six areas, a few with eight, ten and twelve, a good many with fourteen and a few with sixteen and eighteen. The structure of these is absolutely identical with that of the six- rayed forms, and it is as absurd to separate them as it would be to separate forms of A. Heliojjelta with six areas from those with more. Other forms commonly ranked under A. vulgaris are simply valves of A. adriaticus with the pseudo-raphes wanting, as already described, while others seem to be similar, but with deeper and more abrupt undulations. The undulations in A. adriaticus are very shallow, so much so that Grunow origin- ally described it as flat ; but in view of the considerable variation in this respect found in the valves of A. undulatus and other species, the character would seem to be of doubtful importance. Probably the nearest approach to a really flat condition is found in the three-sided A. mari/landicus, in which the six areas show a very slight difference of level near the centre only, else- where blending with each other imperceptibly. This species has a more or less distinctly three-sided umbilicus, and appears to be identical with the Symbolophora trinitatis of Ehrenberg. Ralfs has argued against this view on the ground that >S'. trinitatis is W. M. BALE ON SOME OF THE DISCOID DIATOMS. 43 circular, while A. marylandicus is three-sided, but in Atlantic City slides valves of the latter species are found in which the divergence from the perfectly circular form is scarcely perceptible, so the objection falls to the ground. It is sometimes stated as a character of the genus that the depressions of one valve correspond to the elevations of the other, so that the frustule is radially undulated as a whole. That this is not alwavs the case is evident from the fact that the two valves have often a different number of areas. But I find on comparing a number of species that there is considerable variation in regard to the undulations. First we have forms in which the undula- tions extend to and include the rim itself, so that one valve necessarily fits into the other. A striking example is A. trilingu- latics, in which the whole valve is so strongly undulated that only three points of the margin can be seen at any one focus. Then we have such species as A. undulatus and A. Heliojwlta, in which the undulations do not extend outward to the margin. Apart from the border itself, the sub-marginal zone is about on a level throughout, but the one set of areas is inflated as much above that level as the other is below it. The border itself slopes down rather steeply, but the depressed areas often reach as low a level as the extreme margin. Still, the width of the hoop ensures that such valves may be placed with the depressions opposite each other without coming into contact. Lastly, in A. splendens the depressions do not reach as low as the margin, while the eleva- tions rise considerably above it ; even with a narrow hoop, therefore, there is no question of the depressed areas of opposite valves clashing. According to the definitions of Ralfs and Yan Heurck, a character of the genus is the division of the valve into equal cuneate segments, which would exclude from it the A. hispidus Grunow (Van Heurck, Synopsis, PI. 123, fig. 2), a species which is described as having narrow elevated compartments alternating with wide depressed ones. I believe, however, that the so-called elevated compartments of A. hisjndus are not compartments at all in the same sense as those of Actinoptychiis ; neither are they elevations, but only appear so owing to having depressions on each side of them. The valve is a shallow cone, by far the greater part of which is occupied by about eight or nine broad radial cuneate areas, all of which are depressions. The linear rays or ridges are simply parts of the surface not included in the depressions, but dividing them. These rays slope down evenly 44 W. M. BALE ON SOME OF THE DISCOID DIATOMS. from the umbilicus and join the sub-marginal zone without any interruption of the structure, which indeed is similar all over the valve, except the narrow hyaline border. The valve is very thin, covered with very delicate striae, crossing each other obliquely, and most easily seen on the narrow rays. The secondary markings consist of a fine, delicate, irregular reticulation, at the angles of which are dark points or apiculi, which are larger and darker on the narrow rays and sometimes round the inner border. On each of the linear rays, near the border, is a minute process. In Grunow's figure both the cuneate areas and the dividing rays are abruptly truncate at the border, but my specimens do not agree with this, as the narrow rays widen out in a regular curve towards the border zone, with which they are continuous, the cuneate areas having of course their outer corners rounded off correspondingly, while they do not quite reach the border. Owing to the thinness of the valve, however, and the depressions being by no means abrupt at the outer ends, this character might often pass unnoticed, unless the valve happens to be lying obliquely, when it becomes more conspicuous. Possibly my specimens, which were found in recent gatherings from Port Phillip, may differ specifically from Grunow's guano specimens, but the late Mr. Comber considered them the same. I think the characters by which this species is distinguished from all others of the genus are such as to entitle it to at least the rank of a sub-genus, for which I would suggest the name Radiodiscus. It is possible, however, that it may be brought under the genus Actinodictyon Pantocsek, but I am uncertain of the affinities of that genus, of which I have seen no specimens. I have a single valve, apparently belonging to A. hispidus, which differs in several respects from the usual form. Its depressions are extremely slight, there are no secondary markings and no apiculi, and the cuneate areas terminate in a hyaline band, as in A. splendens, etc.; it also has exceedingly narrow lines (pseudo-raphes) on the narrow areas ; the border is wanting. It may be a varietal form, or possibly an internal disc, but its pseudo-raphes and hyaline bands seem to indicate a closer affinity with such forms as A. adriaticus than would be inferred from the typical form. Journ. Quckett Microscopical Club, Ser. 2, Vol. XII., No. 72, April 1913. 45 SOME NOTES ON BRITISH FRESHWATER RHAB- DOCOELIDA— A GROUP OF TURBELLARIA. By Henry Whitehead, B.Sc. (Read January 28th, 1913.) Plate 4. The members of the group Rhabdocoelida are very similar as regards appearance, shape and movements to the Infusoria, though they are generally much larger and their complicated internal structure enables them to be distinguished at a glance. The Rhabdocoelida form a branch of the group Turbellaria, to which the larger Planarians found in fresh water also belong. The Turbellaria, in turn, together with the Liver-flukes and Tape-worms, are included in the phylum Platyhelminthia or Flat-worms. The British marine Turbellaria have been monographed by Prof. Gamble (12), and our President has taken an active part in the study of the land Planarians of Australasia. The freshwater Turbellaria have apparently received but little attention in this country, though Prof. Gamble publishes a list of British species in the Cambridge Natural History (14). As the larger freshwater Planaria (Tricladida) cannot be regarded as microscopic objects, and are therefore of no special interest to the Club, the writer proposes, in this paper, to deal only with the group Rhabdocoelida. Yon Graff has written two monographs on this group, and has devoted much time to valuable work on anatomical features ; and it is chiefly from these sources that the information con- tained in this paper has been derived. The writer does not propose dealing in detail with the anatomy, but rather to deal with the Rhabdocoels from a general point of view, emphasising matters of particular interest to the field naturalist. The freshwater Rhabdocoels vary in size from 1/2 5th to half 46 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA an inch in length. They are generally found in ponds, lakes and ditches, and less frequently in running water. Like many other microscopic inhabitants of ponds, they appear in great abundance at certain seasons of the year and then suddenly disappear. The body is more or less transparent, slightly flattened, and is provided with cilia. The Turbellaria are remarkable for peculiar secretions given off from the epidermis. These secretions are of two distinct kinds — one a mucous fluid, and the other con- sisting of very small solid bodies, or rhabdites, which, on coming in contact with the water, produce mucus. Several forms of rhabdites have been described (spindle-shaped, rod-shaped, egg- shaped and spherical). They are formed in special glandular cells which lie beneath the epidermis, and the rhabdites pass to the surface by means of minute ducts. Another interesting feature is the presence, in certain species, of nematocysts similar to those found in Hydra.* The Rhabdocoels are provided with a mouth, a pharynx and an unbranched, sac-like gut. The position of the mouth varies and affords a valuable generic character. It may lie at the extreme anterior or in a median position anywhere along the ventral surface as far down as two-thirds of the body length. The excretory system consists of renal organs which are, in some cases, somewhat complicated in structure. The nervous system is simply, and comprises a two-lobed brain and a pair of nerves running along the body close to the ventral surface. In some species the pigmented eyes are clearly defined, in others the eye pigment is scattered, and in some cases eyes are absent. Some of the freshwater Rhabdocoels have at their anterior end pit-like depressions which contain cilia (PI. 4, fig. 3, cp). The ciliated pits rest upon a group of ganglion cells which are connected with the brain. Similar structures are found in Nemertine worms, and some zoologists consider that this suggests affinity between the groups. Another interesting organ is the statocyst, which is present in some species. This consists of a cavity containing fluid, in which is suspended a highly * Mr. Scourfield has recently called my attention to a paper by C. H. Martin (20) on this subject. The author shows conclusively that the nematocysts are derived from the prey upon which the Turbellarian feeds. A GROUP OF TURBELLARIA. 47 refractive particle of calcium carbonate — the otolith (or statolith). The statocysts serve as organs of equilibration. Reproduction is, in most cases, sexual. The animals are hermaphrodite, but the male organs ripen first. The sexual organs are very complicated, and the details of their structure are of great value in classification. On this account it is often impossible to determine the species of immature individuals, and sometimes it is necessary to have specimens in both the male and the female stages before identification can be certain. Fresh- water Turbellaria undergo no metamorphosis, and newly hatched individuals are similar to their parents in general appearance. Asexual reproduction occurs only in the section Hysterophora. A chain of individuals is formed by the development of mouths, eyes, etc., at intervals along the body. Constriction of the body and gut then follow, and fresh individuals are produced by fission. The process is illustrated in PI. 4, fig. 3. Some species which reproduce asexually throughout the year develop sexual organs in the autumn. These produce eggs which lie dormant through the winter. Considerable interest has recently been aroused in certain green or yellow cells which are found in the bodies of some species of Turbellaria. The green cells contain chlorophyll and are able to decompose carbon dioxide in the presence of sunlight. Two marine species, Convoluta roscoffiensis and G. jmradoxa, found on the coast of Brittany, have been the subjects of detailed study, and the results have been summarised by Prof. Keeble in a little book entitled Plant- Animals. The genus Convoluta belongs to a group of Turbellaria, the members of which have not, up to the present, been found in fresh water. The green cells or zoochlorellae, as they are termed, are now regarded as algae similar to Chlamydomonas. In the case of Convoluta it is certain that the presence of zoochlorellae is of benefit to the Turbellarian, and that the relationship is a true symbiosis. Von Graff (17) mentions twenty-five species of freshwater Rhabdocoels in which green cells have been found. The fresh- water species containing zoochlorellae have not been well studied, and some zoologists doubt whether there is mutual benefit in the association. This aspect of the subject will, however, be dealt with later. The Rhabdocoelida live under various conditions, but generally 48 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA — prefer still or gently flowing water to rapid streams. One species, Prorhynchus stag7ialis, is sometimes found on moist earth. Many of the aquatic forms are free swimmers, and may be captured in the net in the same way as rotifers and water-fleas ; others live in mud. In the latter case it is best to pour a little of the mud into a glass tank containing clear water, and to remove any Rhabdocoels by means of a pipette. They should be examined in a live box, and it will be found that a slight pressure is necessary to ensure making out their internal structure. They are very difficult to prepare in a satisfactory manner as permanent objects, and the writer has made numer- ous experiments with a view to narcotising them, but with little success. Eucaine, chloroform, ether and alcohol are of no use. The difficulty seems to lie in the fact that the rhabdites are discharged as soon as the animal is irritated, and these, of course, produce quantities of mucus. Moreover, the epidermal cells get destroyed during the process. The only satisfactory method of killing seems to be by means of some hardening re- agent, like corrosive sublimate solution, which takes effect before the mucus and rhabdites can be discharged. The following well- known method is the best. The specimen is placed in a watch- glass with a little water, the bulk of which is withdrawn by a pipette. A drop of Lang's Fluid is then delivered from a pipette on the side of the watch-glass and is allowed to run over the animal. Death is almost instantaneous, and but little shrinkage takes place. Even with this method the writer has not yet succeeded in killing species of Mesostoma without disruption. After remaining in Lang's Fluid from ten to fifteen minutes, the specimens are removed to 45-per-cent. spirit. They are afterwards passed through alcohol of increasing strength, stained with borax-carmine and mounted in Canada balsam in the usual way. Some of the Rhabdocoels appear to be entirely vegetarian in diet, and consume desmids, diatoms and unicellular algae. In fact, care is sometimes necessary to distinguish the food from the zoochlorellae. The latter, however, never occur in the gut. The majority of species take animal food, which consists of water- fleas, small worms, etc. We may now consider a few typical species which have been taken by the writer in the neighbourhood of London. A GROUP OF TURBELLARIA. 49 Catenula lemnae (Ant. Dug.). Occurs in ponds and lakes, and often appears suddenly in considerable numbers in collections of rain-water during the spring and summer, and disappears as rapidly as it comes. It is white and thread-like in appearance, consisting of a chain of 2 — 4 individuals (rarely more) and attaining a length of 5 mm. The body possesses a well-defined head lobe, which is marked off by a slight constriction and a ring of comparatively long cilia ; a statocyst is present. The usual mode of repro- duction is by fission, but sexual organs are developed when the pond or ditch begins to dry up. Microstomum lineare (Mull.) (PI. 4, fig. 3). This species is very similar to the foregoing, but the colour is yellowish or greyish brown. It is usually found in the form of a chain of zooids of which there may be as many as 18. The colony attains a length of 8 mm. Each zooid develops a pair of red eyes, behind which may be seen the ciliated pits. The skin is thickly clad with cilia. No rhabdites are present, but nematocysts, similar in form to those of Hydra, are present (20). The figure shows the manner in which new individuals arise, and various stages in the formation of mouths may be seen. The gut is common to all the zooids in the chain, until fission takes place. The writer has seen desmicls which had been swallowed for food pass along the common gut from one zooid to another. Sexual organs are sometimes produced, and the ripe eggs are oval in shape and orange or dark red in colour. This species is fairly common in stagnant or slowly moving water. It has been found in thermal springs at a temperature of 130° F. and also in brackish water. It moves slowly on a surface, but is a graceful and swift swimmer. Dalyellia viridis (G. Shaw) (PI. 4, figs. 1 and 2). Examples of this species attain a length of 5 mm., and are generally spinach-green in colour. The colour is due to the presence of algal cells Which lie beneath the epidermis. The body is truncated in front, widens towards the middle and then tapers towards the tail. There are two bean-shaped eyes. There is a very distinct pharynx and the gut is sac-like. Journ. Q. M. C, Series II.— No. 72. 4 50 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA Specimens of this interesting Rhabdocoel were taken in one of the ponds in Richmond Park, on the occasion of the Club's visit on April 13th, 1912. The following week the writer took specimens from a pond near Chigwell Row, Essex. It was noticed that the animals had a number of eggs (in one instance 49 were counted) in the spongy body tissue, and individuals in this condition avoided the light. As far as could be ascertained, no eggs were deposited by the living animals, but, on death, the eggs were liberated on the decomposition of the body of the parent. So far none of these eggs have hatched. Prof. Sekera (16) of Tabor, Bohemia, succeeded in keeping specimens alive for some time, and the following notes are taken from the account of his observations. Young specimens were taken in ponds in March, when ice was still floating on the water. The animals were colourless, but as soon as they approached maturity, and the sexual pore developed, it was noticed that a few algal cells (zoochlorellae) had entered the body cavity by this means. Streaks of green granules then began to spread from this region and extend beneath the cuticle over the whole body, until finally the animal became quite green. (T would remark, in parenthesis, that mature specimens show distinct lines or bands devoid of zoochlorellae.) Solid food in the form of diatoms, rotifers, etc., was ingested during this period. While rapid division of the algal cells was taking place, they formed spherical or ellipsoid clusters, each group being surrounded by a colourless membrane. The membrane finally disintegrated and the algal cells were dispersed in narrow irregular lines or bands. The mature zoochlorellae showed no signs of an enveloping membrane. The animals exhibited at this period a distinct tendency to crawl towards light (phototactic), but sank to the bottom of the vessel at night. During the third week eggs were formed in the body cavity. The worms at this stage began to avoid the light and spent the whole day at the bottom of the vessel or under vegetation. During the first week in May the animals died off rapidly, and with the decomposition of the body the eggs were liberated. The algal cells were set free and continued to live, and developed an investing membrane, then passed into a resting stage, probably awaiting an opportunity of invading the next generation of Dalyellia. Prof. Sekera thinks that the alga is of little or no value to the A GROUP OF TURBELLAEIA. 51 animal in the way of providing food, his reasons being that closely allied species, living under similar conditions, do not con- tain algae, and that solid food is ingested after the algal cells are fully developed. The writer hopes to investigate this question more fully, for Sekera's argument does not seem to be quite conclusive. Sir J. G. Dalyell (1) wrote an account of this interesting species in 1814, and states that it sometimes occurs in large numbers, and then suddenly disappears. He found his specimens chiefly in the spring, but some were found in the autumn. Mesostoma Spp. (PL 4, fig. 4). Some of the species of Mesostoma produce two kinds of eggs — thin-shelled and thick-shelled. The thick-shelled eggs, which contain a large quantity of yolk, are produced in the late summer and lie dormant during the winter. The young hatched from these so-called " winter " eggs, when less than half the size of the parent commence to produce thin-shelled eggs with but little yolk. It is probable that these eggs are unfertilised ; they are produced in great numbers and begin to hatch in April and May. The young hatched from these eggs attain full development and produce thick-shelled " winter " eggs, which have been fertilised (14). There is some difference of opinion amongst observers as to the precise nature of the life-cycle in this genus. See von Graff (17). They vary in size from 3 to 15 mm. in length according to the species and condition. They live in clear, still or slowly flowing water and swim or creep over water-plants. Their food consists of entomostraca, small worms, etc., which are sometimes caught by means of slime threads. Bothromesostoma personatum (Schm.). Specimens of this species attain a length of about 7 mm. and are easily identified by two white patches which look like large eyes on each side of the "head." The rest of the body is either grey or black. The writer has taken specimens on the leaves of water-lilies and creeping on the surface film, at Staines and at the East London Waterworks. The genus Bothromesostoma is closely allied to Mesostoma, and like the latter produces both summer and winter eggs. 52 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA Gyratrix hermaphroditus Ehrbg. (PI. 4, fig. 5). This species appears to be widely distributed. It is about 2 mm. in length, is almost transparent and is a rapid and graceful swimmer. It can easily be recognised by the com- paratively long stiletto at the posterior extremity. This weapon, although connected with the male copulatory apparatus, is furnished with a gland which probably secretes a poison of some kind and is used by the animal when attacking its prey. It has a well-marked proboscis, behind which are two eyes. The mouth and pharynx are situated near the middle. As a general rule, only one egg-capsule is present, and this produces one or two embryos. The field is almost unworked as regards this country. Von Graff records 110 species of Ehabdocoelida from Germany. As far as the writer can ascertain, only 30 species have been recorded from the British Isles. It is hoped that this short account mav arouse the interest of some of the members of the Quekett Microscopical Club in these interesting animals. List of British Species. In the following list the descriptions of the species will, unless otherwise stated, be found in Die Silsswasserfauna Deutschlands, Heft. 19. The initials H. W. after the localities denote that the species has been found by the author at those places : Sub-order RHABDOCOELA. Section Hysterophora. Fam. CATENULIDAE. Catemila lemnae Ant. Dug. Near Cork (14). Stenostomum leucops (Ant. Dug.). Common (14) ; Clare Is. (24) ; Staines (H. W.). S. unicolor 0. Schm. Clare Is. (24). Journ. Q.M.C. Ser. 2, Vol. XII., PI. 4, rw H W del. Rhabdocoelida. A GROUP OF TURBELLARIA. 53 Fam. microstomidae. Microstomum lineare (Miill). Fresh water (14) : Chigwell : Higham's Park, (H. W.) ; " In all Scottish lochs " (19) ; near Dublin (21). Macrostomum appendiculatum (0. Fabr.) (= hystrix, Oe). Stagnant water (14) ; Clare Is. (salt water) (24). Fam. PRORHYNCHIDAE. Prorhynehus stagnalis M. Schultze. In Devonshire rivers (14) ; L. Lomond (19) ; Fenton Tower, E. Scotland (9). P. curvistylus M. Braun. Near L. Lomond (19). Section Lecithophora. Fam. DALYELLIIDAE. Dalyellia diadema Hofsten (18). Chigwell Row (H. W.). This species appears to have been recorded only once before, viz. in the Bernese Alps. D. viridis (G. Shaw) (= heUuo Miill). Generally distributed (14) ; Richmond Park, Chigwell Row (H. W.) ; Edinburgh (9). D. armigera (O. Schm.). Millport (14). D. Schmidtii (L. Graff). Millport (14). D. millportianus (L. Graff) (9). Millport (9). Jensenia agilis Fuhrm (= serotina, Dorner). Richmond Park, Epping Forest (H. W.). J. truncata (Abildg.). Abundant in fresh water (14), L. Lomond (19). Phaenocora (= Derostomum) punctatum Orst. Theydon Bois (H. W.) ; Edinburgh (9). Opistomum Schultzeanum Dies. L. Lomond (19). 54 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA Fam. typhloplanidae. Rhynchomesostoma rostratum (Miill). Widely distributed (14) ; Millport, Edinburgh (9). Typhloplana viridata (Abildg.) ( = Mesostoma viridatum M. Sch.). Manchester (14) : Clare Is. (24). Mesostoma productum (0. Schm.). Cambridge (14). M. lingua (Abbild.). Cambridge (14). M. Ehrenbergii (Focke). Cambridge (14). M. tetragonum 0. F. M. Cambridge (14). M. Robertsonii L. Graff. (9). Millport (9). M. flavidum L. Graff. (9). Millport (9). Bothromesostoma personatum. (0. Schm.). Preston (14) ; Staines, E. Lon. Waterworks (H. W.). Fam. POLYCYSTIDIDAE. Polycystis Goettei Bresslau. Nr. Abergavenny, L. Lomond (19). Fam. GYRATRICIDAE. Gyratrix hermaphroditus Ehrbg. Common in fresh water (14) ; Chigwell Row (H. W.) ;. St. Andrews (salt water) (9) ; Clare Is. (salt water) (24). Sub-order ALLOEOCOELA. Fam. OTOPLANIDAE. Otomesostoma auditivum (Pless.) ( = Monotus morgiensis et relictus Du Plessis). Deep waters of Scottish lochs (19). A GROUP OF TURBELLARIA. 55 Fam. BOTHRIOPLANIDAE. Bothrioplana sp. ? Manchester (14). Euporobothria bohemica (Vejd.). Tarbet, L. Lomond (19). Bibliography. Confined to the more important works or to papers quoted. 1. 1814. Dalyell, J. G. Observations on Planariae. 2. 1848. Schmidt, E. 0. Die Rhabdocoelen (Strudelwiirmer) des Siissenwassers. 3. 1853. Dalyell, J. G. The Powers of the Creator, vol. ii. 4. 1865. Johnston, G. A Catalogue of the British Non-para- sitical Worms in the British Museum. 5. 1867. Lankester, E. R. Planariae of our Ponds and Streams. Pop. Sci. Rev., vi., pp. 388-400. 6. 1868. Houghton, W. Our Freshwater Planariae. In- tellectual Observer, xii., pp. 445-449. 7. 1878. Jensen, O..S. Turbellaria ad litora Norvegiae. 8. 1879. Hallez, P. Contiibutions a l'histoire naturelle des Turbellaries. 9. 1882. Graff, L. von. Monographie der Turbellarien. I. Rhabdocoeliden. 10. 1885. Braun, M. Die Rhabdocoeliden Turbellarien Liv- lands. 11. 1885. Graff, L. von. Article " Planarians " in Encyc. Brit. Ninth Edition. 12. 1893. Gamble, F. W. Contributions to a knowledge of the British Marine Turbellaria. Quart. Journ. Micro. Science, vol. xxxiv., p. 433. 13. 1894. Fuhrmann. Der Turbellarien der Umgebung von Basel. Revue Suisse de Zoologie. 14. 1901. Gamble, F. W. Flatworms and Mesozoa in Cam- bridge Nat. Hist., vol. ii. 15. 1901. Benham, W. B. Lankester's Treatise on Zoology. Pt. IV. Platyhelmia. 16. 1903. Sekera, E. Einige Beitrage zur Lebensweise von Vortex helluo. Zool. Anz., xxvi., pp. 703-710. 56 H. WHITEHEAD ON BRITISH FRESHWATER RHABDOCOELIDA. 17. 1904-8. Graff, L. vox. Das Thierreich, Turbellaria. I. Acoela und Bhabdocoelida. 18. 1907. Hofsten, Nils von. Studien iiber Turbellarien aus dem Berner Oberland. Zeitschr. f. wiss. Zoologie, lxxxv., pp. 391-654. 19. 1908. Martin, C. H. Notes on some Turbellaria from the Scottish Lochs. Proc. Roy. Soc. Edin., vol. xxviii., pp. 28-34. 20. 1908. Ibid. The Nematocysts of Turbellaria. Quart. Journ. Micro. Sci., vol. lii., pp. 261-277. 21. 1908. Southern, R. Handbook to City of Dublin. Brit. Assoc. 22. 1909. Graff, L. von. Die Siisswasserfauna Deutschlands. Heft. 19. 23. 1911. Ibid. Acoela, Bhabdocoela und Alloeocoela des ostens der vereinigten staaten von Amerika. Zeitschr. wiss. Zoologie, xcix., pp. 1-108. 24. 1912. Southern, R. Clare Island Survey. Pt. 56. Platy- helmia. Proc. Roy. Irish Acad., xxxi. Description of Plate 4. Pig. 1. Dalyellia viridis, entire, x 15. 2. Chitinous copulatory organ of D. viridis, X 150. 3. Microstomum lineare, entire, x 20. 4. Mesostoma sp., entire with thin-shelled eggs, x 20. 5. Gyratrix hermaphroditus, entire, X 45. b c, bursa copu- latrix ; c, cocoon ; c p, ciliated pit ; e, egg ; g, gut ; m, mouth ; o v, ovary ; p, poison-sac ; p h, pharynx ; p rf proboscis ; s t, stiletto ; it t, uterus. Journ. Quekett Microscopical Club, Ser. 2, Vol. XII., No. 72, April 1913. 57 THE ROTIFERA OF DEVILS LAKE, WITH DESCRIP- TION OF A NEW BRACHIONUS. By Charles F. Rousselet, F.R.M.S. {Read January 2%th, 1913,) Plates 5 and 6. Devils Lake, the largest body of water in North Dakota, U.S.A., is approximately 30 miles long by 5| miles wide at its broadest part, and of very irregular shape. It receives its water from a territory which forms an inland drainage basin extending northwards as far as the Turtle Mountains. From the records it appears that the level of the lake has fallen 14 feet since 1883 (when it stood at 1,439 feet above sea- level) and 16 feet between 1830 and 1883, making a total recession of 30 feet in eighty years with a corresponding shrink- age of the area of the lake. At the time of its highest level the lake had an overflow outlet at its eastern end into Stump Lake lying further east, and it is probable that this high-water level was reached many times in past centuries through periods of scanty rainfall succeeded by periods of unusually abundant pre- cipitation. In 1910 the level of the water stood at 1,425 feet above sea-level, but fluctuates about 4 feet between very dry and wet periods. The lake has had no outlet for a long period, and as the result of evaporation the water has become brackish, the salinity increasing gradually by concentration, until at the present time the water has a specific gravity of 1*0076 (the sp. gr. of sea water being 1*027). Besides common salt the water contains appreciable quantities of sodium sulphate and magnesium sulphate, carbonate and bicarbonate, so that it is alkaline as well as brackish, and this no doubt accounts for the very peculiar and remarkable Rotif erous 58 C. F. ROUSSELET ON THE ROTIFERA OF DEVILS LAKE fauna it contains, which is abundant in numbers but very re- stricted in species. Since 1910 a Biological station has been established on the shores of the lake by the Legislative Assembly of the State of North Dakota, under the control of the Biological Staff of the State University. At the request of Prof. R. T. Young I have at various times examined samples of plankton collected by him in July 1910 and May 1912, and have found therein only the following seven species of Rotifera, the majority of them rare, strange and unusual forms : Triarthra longiseta Ehrenberg (a single specimen, possibly accidental). Pedalion fennicum Levander. {Very abundant.) Asplanchna Silvestrii Daday. (Very abundant.) Brachionus Midleri Ehrenberg. (Few.) Brachionus satanicus Rousselet. (Very abundant.) Brachionus spatiosus Rousselet. (Very abundant.) Brachionus pterodinoides sp. nov. (Few.) Two of these forms I have already described as new,* and have now to introduce a third still stranger species. The single specimen of Triarthra may have been introduced by accident in one of the tubes. Rotifera are essentially freshwater animals, and brackish or salt water does not suit the great majority of species; this ex- plains the paucity of species living in Devils Lake. This fact does not militate against the theory of cosmopolitan distribution of the class, on the contrary it confirms it, for Pedalion fennicum is known from brackish lakes only in Finland, Egypt, Central Asia, Asia Minor, etc. The presence in the lake of the rare Asplanchna Silvestrii suggests that the " Lago di Villa Rica," in Chile, from which it was first obtained, is a brackish lake. Perhaps Prof. Silvestri, who obtained Daday's * Journ. Q.M.C., Ser. 2, Vol. XL, pp. 162 and 373 (April 1911 and 1912). WITH DESCRIPTION OF A NEW BRACHIONUS. 59 material, would be good enough to confirm or disprove this suggestion. Brachionus pterodinoides sp. nov. (PI. 6, fig. 1). This new Brachionus, of which only very few specimens were found, possesses a type of lorica new to the genus, and appears to have done its best to try to deceive the systematic student by making itself look as closely as possible like a Pterodina. For quite a considerable time I was unable to decide whether the animal belonged to the genus Brachionus or Pterodina until I found one specimen with the foot and its two small toes protruding, which decided the question. As will be seen on referring to PI. 6, fig. 1, the lorica is nearly circular in shape, greatly compressed and flattened dorso-ventrally, and possesses a foot-opening situated just below the middle on the ventral plate, a most unusual situation for a Brachionus, but usual in Pterodina. The dorsal plate of the lorica is greatly extended posteriorly beyond the foot-opening, and under this projecting cover the eggs are carried. The lorica is smooth except anteriorly, where six small ridges mark the continuation of the six frontal spines. The mental edge is a nearly straight line and without indentation. As far as could be made out in the few preserved specimens available, the internal anatomy of this species appears to be normal. In one specimen the wrinkled foot was extended, showing two small pointed toes, as shown in fig. \c. The lateral antennae protrude high up above the middle on each side. I am greatly indebted to Mr. F. P. Dixon-Nuttall for the three figures giving an excellent idea of the form of this new species and new type amongst the Brachionidae. Size of lorica, length 285 /x (l/89th inch), width 224 fi (1/1 14th inch). Brachionus satanicus Rousselet (PI. 6, fig. 2). When describing this species two years ago * I had specimens only which had been obtained in a plankton collection made in * Journ. Q.M.C., Ser. 2, Vol. XI., p. 162 (1911). 60 C. F. ROUSSELET ON THE ROTIFERA OF DEVILS LAKE Devils Lake in the month of July 1910, and all these had the shape shown in the figure, with two long, curved and widely- separated posterior spines. Last year I obtained from Prof. Young a collection made in the month of May 1912, much earlier in the season, when the weather in North Dakota is still cold and the water chilly. Together with the fully developed forms in this collection I found a much smaller form, with short posterior spines, curved inwards and other unusual features as represented in PI. 6, fig. 26-/. The six frontal spines and the mental edge are identical with those of the larger specimens, but the shape of the body and the form and size of the posterior spines are very different, and, strangest of all, the foot-opening is situated on the postero-dorsal side of the lorica, a quite unheard-of position in this genus. My first impression was that these were young animals just hatched from eggs, but this is evidently not so, for some specimens were seen carrying their eggs at the base of the foot on the dorsal side, and they were therefore adults reproducing freely. I can only conclude that this represents a case of dimorphism, possibly a winter form which gradually, in successive generations, transforms itself into the larger form with extended and expanded posterior spines. In saying this I do not mean that the smaller forms (PI. 6, fig. 26-c) can themselves grow into the form of fig. 2a, but that their offspring will in a few genera- tions more and more resemble the larger form. Intermediate forms between the two types figured were not seen. In order to follow up this transformation it will be necessary to obtain plankton collections made about twice a month throughout the year, which at present are not available. It certainly is not easy to see how the dorsally situated foot-opening can change into the median posterior position of the larger form, but it is known that in the case of some Asplanchna (A. amphora, A. Sieboldii) the transition from humped into saccate forms and other changes take place suddenly, from one generation to the next, produced apparently through a change of diet and temperature, as shown by the recent researches of Dr. Arno WITH DESCRIPTION OF A NEW BRACHIONUS. 61 Lange * and Prof. Powers. t Should these changes in B. satanicus be confirmed, it will be the first record of true dimorphism in the genus Brachionus. Fig. 2e and f represent variations in the shape of the posterior spines of the smaller form. Fig. 2a-f were drawn from my own preparations by Mr. F. R. Dixon-Nuttall, to whom I am greatly indebted for these accurate and beautiful drawings. The large form fig. 2a measures 408 /x (l/62nd inch), and the small form 250 /x (1/1 00th inch), in both cases including the posterior spines. Asplanchna Silvestrii, Daday. PI. 5, figs. 1—9. This fine and rare species was first described by Daday in 1902,J and found by him in plankton collections made by Dr. Silvestri in 1899 in the Lago di Villa Rica in Chile. I have not been able to ascertain if this lake is brackish or not, Prof. Daday having no information on this point, but the presence therein of Pendalion fennicum seems to make it highly probable, for the latter species has never yet been found in fresh water. In the collections from Devils Lake I found Asplanchna Silvestrii in great abundance, and moreover it presented a marked dimorphism, and even polymorphism, for all gradations from plain saccate forms to fully developed double-humped animals were represented in the same gathering. PI. 5, figs. 1 — 4 represent three of the forms. It is not possible for me to say wThich of these forms appears first, or which is hatched from the resting-egg, and what causes these changes of form. According to the observations of Prof. J. H. Powers, of Nebraska Univer- * Zur Kenntnis von Asplanchna Sieboldii, Zool. Anz. Bd. 38, pp. 433-441, November 1911. f A case of Polymorphism in Asplanchna simulating mutation. American Naturalist, Vol. XL VI., 1912. \ Beitrage zur Kenntnis der Siisswasser Mikrofauna von Chile. Ter- meszetrajzi Fiizeteh, 1902. 62 C. F. ROUSSELET ON THE ROTIFERA OF DEVILS LAKE sity, who has lately published an account of similar changes in A. amphora found by him in a brackish pool, it is caused by a change of diet, from vegetable to more substantial animal food, and even cannibalistic fare. Prof. Powers found that the animals hatched from resting-eggs were invariably saccate, and that the humped and larger campanulate forms developed from these. Asplanchna Silvestrii is a very large and powerful animal, as is shown by its ability to capture, swallow and digest the large and vigorous Diaptomus which abound in this lake ; one of these Copepods was seen to more than fill its stomach. The male was also found ; it is humped, but the side humps are not bind as in the humped female, as shown in figs. 5 and 6 ; the fertilised resting-egg is represented in fig. 9. The jaws are of the usual type, but are different from those of any other species of the genus, as is shown by fig. 7. The rami are massive, and have a semi-circular cut-out near the tip, which is peculiar ; they have also a strong basal hook and median inner tooth. One of the rami, the one on the right side when the basal hooks are uppermost, has a broad flange near its apical tooth ; this serves as a stop for the opposite tooth to prevent the two rami overlapping and interlocking. The prominent lateral humps differ markedly from those of other humped species, such as A. Sieboldii and A. amphora. In A. Silvestrii these are bifid, having a constriction, more or less pronounced, above the middle of the hump, giving it a double rounded outline (fig. 1) ; on the dorsal side there is a pointed hump near the middle of the body (fig. 2). In intermediate forms the humps are less prominent until the purely saccate form is reached (fig. 3), which in shape does not much differ from that of A. Brightwelli. Prof. Powers has shown that no single animal goes through these various shapes ; they are born with the shape they possess and do not change it in their lifetime, but their jDrogeny may have a different shape from the parent. A young humped individual may be seen in WITH DESCRIPTION OF A NEW BRACHIONUS. 63 the uterus of a saccate female. The change takes place more or less suddenly from one generation to the next. The general anatomy of A. Silvestrii follows that of other allied species, and but few points need be mentioned. The two gastric glands are large and kidney shaped, and are attached to the long and rather wide oesophagus. The stomach has the usual structure of large, dark-coloured granulated cells. The ovary has the form of a narrow horseshoe-shaped band with a single row of germ cells. An enlarged view of one of the lateral canals with the contractile vesicle is given in fig. 8. The flame cells are closely set and numerous, numbering over thirty ; the fine tube to which they are attached adheres for some distance to the nerve-thread of the ventro-lateral antenna on each side. The sense organs consist of three pairs of antennae, namely two on the front of the head, two dorso-lateral and two ventro-lateral in position, each ending in a rocket-shaped organ with a tuft of stiff hairs on the outside. Two finger-like, fleshy processes are seen, one on each side of the head close to the corona. Daday mentions that the animal has three red eyes, but I could discover only a single small cervical red eye, situated on the small brain. The male (figs. 5 and 6) is of usual structure, and has two lateral humps, like the male of A. amphora. Greatest size of female 1,150 /x (l/22nd inch) in length ; male 408 jx (l/64th inch) ; jaws 164 fx (l/155th inch) ; resting-egg 195 /x (1/1 20th inch) in diameter. I am greatly indebted to Mr. Hammond for the excellent figures of A. Silvestrii on Plate 5. It is quite possible that farther plankton collections, and particularly collections made amongst the aquatic vegetation near the shores and in the bays of Devils Lake, may reveal additional species of Rotifera, but a great crowd of freshwater forms cannot be expected to inhabit this brackish and alkaline lake. 64 C. F. ROUSSELET ON THE ROTIFERA OF DEVILS LAKE. Explanation of Plates 5 and 6. Plate 5. Fig. 1. Asplanchna Silvestrii Daday, characteristic female with double humps, dorsal view, x 50. 2. A. Silvestrii, side view, x 50. 3. A. Silvestrii, saccate form, dorsal view, x 50. 4. A. Silvestrii, intermediate form, ventral view, x50. 5. A. Silvestrii, male, side view, x 68. 6. A. Silvestrii, male, dorsal view, x 68. 7. A. Silvestrii, the jaws, x217. 8. A. Silvestrii, vascular system with contractile vesicle, x 150. „ 9. A. Silvestrii, resting-egg, x 65. Plate 6. Fig. la. Braehionus pterodinoides sp. nov., dorsal view, x 196. ,, lb. B. pterodinoides, ventral view, x 196. „ lc. B. pterodinoides, side view, x 196. „ 2a. Braehionus satanicus Rousselet. Normal type, x 180. „ 2b. B. satanicus, small seasonal form (winter), dorsal view, X180. „ 2c. B. satanicus, small seasonal form (winter), ventral view, Xl80. ,, 2d. B. satanicus, small seasonal form (winter), side view, X 180. „ 2e. B. satanicus, small seasonal form (winter), variation in posterior spines, x 200. ,, 2f. B. satanicus, small seasonal form (winter), variation in posterior spines, x 200. Joum. Quekett Microscopical Club, Ser. 2, Vol. XII., No. 72, April 1913. Journ.Q.M.C. Ser. 2,Vol.Xir,Pl. 5. 3 ^-Xr"-' 1 * . 9 A. R. Hammond del.et lith.. West,>4ewma.n imp. As plan elm a Silvestrii Dadcuy. Journ.QM.C. Ser. 2,Vol.XII.Pl. 6. la / lb. F.R. Dixon -Nuttall del.adnat. A.R.Hammond lith.. West, Newman, imp. Rotifera. 65 THE PRESIDENT'S ADDRESS. BY-PRODUCTS OF ORGANIC EVOLUTION. By Prof. Arthur Dendy, D.Sc, F.R.S. {Delivered February 25th, 1913.) Plate 7. We are all familiar with the fact that in the manufacture of any particular product of human industry the raw material employed is rarely entirely used up, a more or less considerable *• residue generally remaining over after the process is completed. In so far as the prime object of the manufacturer is to produce some one special product, the residue which cannot be employed for this purpose must be regarded as waste. It frequently happens that this waste product is a highly deleterious substance, the difficulty in the disposal of which may constitute a very serious obstacle to the successful prosecution of the industry in question. On the other hand, it also frequently happens that what were primarily waste products may prove to have a value of their own quite apart from the main object at which the manufacturer is aiming. They then cease to be merely waste products and become valuable by-products, perhaps even more valuable than the main product itself. Thus in the distillation of coal in a gasworks the main purpose, that for which the machinery and apparatus are primarily intended, is the production of gas, but coke and tar and other by-products are also produced, all of which are now, I suppose, applied to some useful purpose, and thus have a value of their own. Indeed the existence of coal-tar has given rise to a whole series of new industries, involving the production of almost endless substances, such as the wonderful aniline dyes and so forth, which many people will regard as far more valuable and desirable Jourx. Q. M. C, Series II. — No. 72. 5 66 the president's address. objects than the gas for the sake of which the coal was originally- distilled. The value of a by-product will naturally depend upon the particular circumstances of the case, and what is useless, or even harmful, under one set of conditions may be extremely valuable under another. It may be a question of labour supply or of transport, or it may be that the discovery of some new process of manufacture in a totally different industry suddenly creates a demand for a by-product that was previously almost or entirely worthless. It is perhaps not too much to say that the success or failure of a manufacturer in his business must in many cases depend upon the ingenuity that he exhibits in disposing of his by-products ; but the formation of such products in the first instance cannot be avoided, and they may go on being produced, and constitute a characteristic feature of the industry for a long time, before some new factor in the circumstances of the case may give them a special value of their own. It may well be that this may never happen at all, and the substances in question may simply accumulate in harmless, if unsightly, heaps, or, on the other hand, they may become so offensive, or even dangerous, as to render impossible the continuance of the industry which gives rise to them. In short, it would be difficult to exaggerate the importance of the part played by by-products in the evolution of human industries. Such industries are necessarily subjected to a severe struggle for existence in ceaseless competition with one another, and in this struggle the by-products afford abundant opportunity for the elimination of the least fit by the process of natural selection. The by-products, however, did not themselves arise through any process of selection, but as the unintentional and inevitable results of those chemical and physical changes which accompany the manufacture of the main product. We may thus look upon a human industry as an organism, which undergoes a process of evolution subject to the control of natural selection, and some of the most characteristic features of which are to be found in its by-products. Indeed it may often be recognised and identified by its by-products almost if not quite as readily as by the product for the sake of which it primarily exists. We must not, of course, push our analogy too far, but I hope to THE PRESIDENT'S ADDRESS. 67 be able to convince you that in the evolution of living organisms themselves by-products have played a part not unlike that which they have played in the evolution of industries. You have probably already began to wonder why I should have chosen such a subject as this for an address to a micro- scopical club ; but the reason will now become apparent, for I propose to endeavour to elaborate the ideas which I have been suggesting to you by reference to organisms which have long been favourite subjects with the microscopist, and to characters which can only be investigated with the aid of the microscope. We shall perhaps find nowhere in the animal kingdom a more exact analogy to the utilisation of waste products in human industries than in the curious rotifer Melicerta janus. As you are all aware, this minute but highly complex organism builds for itself a beautiful dwelling-place out of pellets of its own dung. I do not, however, propose to dwell upon such cases as this, and for our present purposes I must ask you to allow me to interpret the term waste products, or if you prefer it, by- products— for it is obvious that the two cannot be sharply distinguished from one another — in a less literal manner. There is, in my opinion, no group of organisms better suited for the illustration of the fundamental principles of organic evolution than the Sponges. This arises from the fact that they combine with an essential simplicity of structure an inexhaustible variation in detail, and that this variation is to a very great extent clearly and precisely expressed in the form of the microscopical calcareous or siliceous spicules of which the skeleton is ordinarily composed. Moreover, it appears that an unusual number of connecting links have been preserved to the present day, so that we are able to trace beautiful evolutionary series in the wonderful spicule -forms of existing species. Take, for example, the siliceous spicules which are so character- istic of the Tetraxonida. These are probably all to be derived from a primitive ancestral form or archetype (fig. 1) consisting of four rays diverging at equal angles from a common centre, like the axes which connect the angles of a regular tetrahedron with its central point. The assumption of this regular geometri- cal form by a non-crystalline substance like the hydrated silica, or opal, of which these spicules really consist, is a very remarkable 68 the president's address. fact, especially when we consider how very widely it is afterwards departed from on most lines of spicule evolution. It has been suggested that the equiradiate and equiangular tetraxon was originally adapted to the interstices in a system of spherical flagellated chambers arranged tetrahedrally. This seems probable enough, but in any case we can safely take this form as our archetype without indulging in speculations as to its origin. If we now imagine one ray of our archetype becoming greatly elongated we get a common form of " triaene " spicule known as the " plagiotriaene " (fig. 2), with a long arm or " shaft " and three short arms or "cladi," but still with all the angles equal. If we imagine the angles which the cladi make with the shaft to be increased, so that the cladi come to point forwards, we get the "protriaene" (figs. 5, 5a); if the cladi extend at right angles to the shaft we get the " orthotriaene " (fig. 3), and if they point backwards we have the " anatriaene " or grapnel spicule (figs. 4, 4a). All these long-shafted triaenes are typically oriented with the cladi at or near the surface of the sponge, and the shaft directed centripetally inwards, so that the entire skeleton acquires a markedly radiate arrangement. The cladi of the orthotriaenes usually form a support for the dermal membrane at the surface of the sponge, beneath which they are spread out tangentially, and their efficiency as a dermal skeleton may be greatly increased by their bifurcation (" dichotriaenes," figs. 6, Ga). In the case of the protriaenes and anatriaenes the distal portions of the shafts, bearing the sharp-pointed prongs or cladi, usually project for some distance beyond the surface of the sponge, and in this position they probably serve either to ward off the attacks of enemies or to entangle minute organisms whose decomposition may supply the minute organic particles upon which the sponge depends for its food supply and which will be carried inwards by the inflowing stream of water. A still more remarkable modification is met with in the " discotriaene," in which the shaft is reduced to a short peg inserted in the middle of a flat disk formed by fusion of the cladi. The entire spicule then assumes somewhat the form of a carpet-nail. In the genus Discodermia we find these disco- triaenes stuck close together all over the surface of the sponge,, and forming an impenetrable mail-armour. THE PRESIDENT'S ADDRESS. 69 In Stelletta vestigium, on the other hand, the cladi are reduced to the merest vestiges, and some, if not all of them, may com- pletely disappear, while the shaft remains greatly elongated and forms practically the entire spicule (figs, la — Id). Possibly the simple " oxeote " spicules of this and allied species (fig. 8) have arisen in this manner. An altogether different line of evolution from the primitive tetraxon archetype appears to have given rise to the typical oxeote spicules (figs. 9, 10) of the monaxonellid division of the Tetraxonida. Here two of the four rays of the primitive tetraxon have probably entirely disappeared, while the remaining two have become extended in a straight line with one another. In the typical " stylote " (fig. 11) and " tylostylote " (fig. 12) spicules probably only a single ray persists, so that the so-called organic centre is situated at one end instead of in the middle. In many species the oxea, styles or tylostyles become ornamented with sharp spinose excrescences (fig. 13). In most of the cases which we have so far considered it is easy to see that we are dealing with adaptive modifications. The orthotriaene, dichotriaene, protriaene, anatriaene and discotriaene are all obviously well suited for the fulfilment of their specialised and differentiated functions, and the evolution of these forms is more or less readily explicable in accordance with the well-known principle of the natural selection of favourable variations. The origin of the linear spicules of the monaxonellid forms by complete suppression of two or three of the rays of the primitive tetraxon is, perhaps, not so easy to account for as is that of the triaene series from the same starting-point. In both cases the determining factor was probably, in the first instance, the development of a radially arranged canal-system, requiring a corresponding radial arrange- ment of the supporting skeleton, which could not be obtained wTith spicules of the primitive tetraxon form. That the evolu- tion of the necessary linear spicules has taken place along different paths in different cases is, however, nothing to be surprised at ; it is merely one of those instances of convergence which are quite as common amongst sponges as amongst other groups of the animal kingdom. In the most primitive tetraxonid sponges, which represent more or less closely the ancestral forms from which both 70 THE PRESIDENT'S ADDRESS. Tetractinellida and Monaxonellida have doubtless been derived, we still meet with some of the earliest stages of spicule evolution. Take, for example, Dercitopsis ceylonica, collected by Prof. Herdman in Ceylon, and described in my report on the Ceylon sponges. Here we find the tetraxon spicule in all its primitive simplicity (fig. 25), but associated with it we get numerous diact spicules (figs. 26a — 26c), evidently derived from the tetract by loss of two of the original rays, and clearly showing, by a swelling or an angulation in the middle, that two rays still remain. From such obvious diactine spicules as these, transitional forms lead the way to the comparatively large, straight oxeote spicules which occur in the same and in many other sponges, and which no longer show any trace of their tetraxon and tetract ancestry. In Dercitopsis and its relations — i.e. in the Homosclerophora — although there may be great differences as regards the size of the various spicules, yet we cannot, as in most of the higher groups, sort these spicules out into two distinct categories — megascleres and microscleres — for innumerable gradations exist between large and small. In the course of further evolution, however, the distinction between megascleres, or skeleton spicules, and microscleres, or flesh spicules, becomes very strongly marked. Both have doubtless had a common origin in the ancestral tetraxon archetype, but whereas the former are obviously adapted as the principal skeletal elements, and are arranged accordingly in the sponge, the latter are usually scattered at random through the soft ground substance like plums in a pudding, and neither in form nor arrangement show any evident adaptation to the requirements of the organism. Indeed, the microscleres are usually so extremely minute, requiring high powers of the microscope to make out their true form, that is impossible to believe that their presence can exercise any important influence upon the well-being of the sponge. Still less is it possible to believe that the particular shape which they may assume, which is often highly remarkable, can be of any consequence to their possessor. There are, of course, exceptions to this, as to every generalisation, and sometimes we find microscleres forming a dense protective external crust, as in the case of the " sterrasters " of Geodia, or projecting into the THE PRESIDENT'S ADDRESS. 71 inhalant canals, where they may perhaps serve to filter the incoming water and guard against parasites, as in the case of the " sigmata " of Esp>erella murrayi ; but in the vast majority of cases it is impossible to assign any value at all to the presence of microscleres. Indeed, the numerous species of horny sponges seem to get on quite as well without these bodies. Nevertheless we find that the microscleres, when present, are characterised by very definite and constant forms, and many of them are amongst the most beautiful and wonderful objects that come under the observation of the microscopist. So constant and characteristic are they that they afford by far the most convenient and most reliable data for the classification of the tetraxonid sponges. Particular species, and even particular genera and families of these sponges, are characterised by the presence of highly specialised forms of microscleres, and in the case of species the characteristic form is almost invariable. There can be no doubt that the microscleres have undergone an evolution along definite lines, and one species of a genus is commonly distinguished from another by differences in the shape of these spicules, which, though constant, appear at the same time to be utterly trivial — as, for example, the difference in the shape of the teeth at the small end of the " isochelae " in Cladorhiza pentacrinus (figs. 23, 23a) and Cladorhiza (?) tridentata (figs. 24, 24a). There may be several kinds of microsclere in the sponge, all characteristic of the species, but a single sponge may contain many thousands, or perhaps millions, of the same kind, all exactly alike in shape and size except for an occasional individual variation such as occurs in all organisms. The shape of the microscleres appears to be quite independent of their position in the sponge, and must obviously be attributed to some specific peculiarity of the ovum from which the sponge developed. It is clearly of a blastogenic and not a somatogenic character, and it is usually much more remarkable and quite as constant as that of the megascleres of the same species. The microscleres of the tetraxonid sponges may be divided into two categories, termed astrose and sigmatose respectively. The former (figs. 14a — 14A) may be derived from the tetraxon archetype by multiplication of the rays — due apparently to meristic variation — accompanied usually by diminution in size of 72 the president's address. the whqle spicule ; at the same time the rays may become spiny or branched in a variety of ways, or even soldered together to form a solid siliceous ball (Geodia). The sigmatose microscleres are more remarkable and more constant in form. They are essentially linear spicules, and appear to be derived from minute diactinal oxea. These may be straight (" microxea," fig. 15) or bow-shaped (" toxa," figs. 16, 18a, 186), or their extremities may become bent over to form hooks (" sigmata," figs. 17a, 176, 19). A very peculiar modification of the sigmata is found in the " diancistra " (fig. 21), which often resemble nothing so much as pocket-knives with the blades half open. From the sigmata have also doubtless arisen the " chelae," * characteristic of the family Desmacidonidae, and, in my opinion, the most wonderful of all sponge spicules. Three different chelae are shown in figs. 22 — 24a. A typical chela consists of a curved shaft, bearing a number, commonly three, of recurved teeth, resembling the flukes of an anchor, at each end. The flukes are sometimes expanded into thin blades, and so also may be the shaft. Sometimes the flukes at the two ends of the spicule are equal in size (" isochelae," figs. 22, 22a), sometimes those at one end are larger than those at the other (" anisochelae," figs. 23 — 24a), while in the genus Melonanchora a very curious effect is produced by the meeting and fusing of opposite flukes of an isochela at the equator of the spicule. Minute differences in the form and number of the flukes and the shape of the shaft appear to be constant, at any rate within the limits of a species ; indeed, the very numerous species of Desmacidonidae are to a large extent distinguished from one another by these characteristics (compare figs. 23, 23a, and 24, 24a). The same constancy of form is to be observed in the sigmata, although here there is less scope for specific differences. In both cases the spicule, instead of remaining smooth, may become more or less roughened by the development of minute projections. This is shown, for example, in the sigmata of the genus Par- esperella (fig. 20), where a row of small projections, like the teeth * It is perhaps unnecessary to discuss here the evidence for believing that the chelae have arisen from sigmata. It is derived partly from the development of the chelae themselves and partly from the occurrence of intermediate forms. THE PRESIDENT'S ADDRESS. 73 of a saw, occurs at each end of the shaft, just where it bends round. Now it appears to me quite idle to argue that minute differ- ences in the form of the microscleres, such as I have just described, are of any importance to the sponge in whose soft tissues these microscopic spicules are scattered without order or arrangement. Nevertheless they constitute, as I have already said, constant specific characters, and have undoubtedly arisen by some process of evolution, one form Lading to another just as in the case of any other characters. Such characters are, of course, by no means confined to sponge spicules ; they may be more or less exactly paralleled, for example, in the frustules of Diatoms, the shells of Foraminifera and Kadiolaria, and the calcareous spicules of Holothurians. Natural selection cannot be directly respon- sible for their origin. How, then, are they to be accounted for? Before attempting to answer this question let us inquire how a microsclere actually arises in the sponge. It appears that, from an early stage in embryonic development, certain cells, known as scleroblasts, or mother-cells, are set aside for the purpose of spicule-formation. These mother-cells have the power of extracting silica in solution from the sea-water which circu- lates through the sponge, and depositing it in the form of solid opal, and in the particular shape characteristic of each spicule. Each separate microsclere arises thus in the interior of a single mother-cell. Let us examine a little more closely the conditions under which it is deposited. The mother -cell is, of course, a nucleated mass of protoplasm, and it appears to be bounded on the outside' by a more or less definite cell -membrane. The spicule, at any rate in the case of sigmata and chelae, appears to be deposited on the inner surface of this membrane, and this fact probably explains why it is curved. If we assume, as seems probable, that the mother- cell continues to grow while the spicule is being deposited, and that the spicule is adherent to the cell-membrane, then we may further suppose that the increasing tension and expansion of the latter may cause the thin siliceous film to split into flukes or teeth. Probably, then, the form of the spicule is largely due to mechanical causes. We cannot, however, explain the minute details of structure so simply as this, for why should the chela 74 the president's address. of one species have always three flukes and that of another always more ? Why should the two ends in some cases be equal and in others unequal 1 Why should the teeth at the small end sometimes be shaped as in fig. 23 and sometimes as in fig. 24 ? and why should some be roughened with spines and others not ? We must, I think, assume that these minute differences are dependent upon minute differences in the constitution of the protoplasm of which the mother-cell is composed. It may be a question of the chemical and physical composition of the cytoplasm in which the spicule is actually deposited, or it may be that the nucleus exerts some direct controlling influence upon the form of the spicule, of the nature of which we know nothing. At any rate we can hardly be wrong in attributing specific differences of spicule-form to corresponding differences in the constitution of the mother-cells by which they are secreted. The remarkable thing is that such differences should be so constant, not only throughout hundreds of thousands of mother-cells in the same sponge, but throughout the mother-cells of all the individuals of the same species. We can only suppose, as I said before, that this constancy depends upon some constant peculiarity of the germ-plasm from which all the cells of the individual and all the individuals of the species originate. Obviously the ferti- lised ovum must contain within itself the potentiality of pro- ducing, amongst other things, all the different kinds of spicules which may happen to characterise the particular species to which it belongs. As development goes on differential divisions must take place whereby all the different kinds of cells of which the adult sponge is composed are segregated, and each mother-cell must ultimately retain the power to secrete only one particular kind of spicule. Now there is strong reason for believing that differential cell-division is effected always by the complex process of mitosis or karyokinesis, which concerns chiefly the chromosomes of the nucleus, and hence I think we may pretty safely conclude that specific differences in the form of the microscleres must depend upon differences in the constitution of the nuclei of the mother-cells, or, in other words, that the nuclei of the mother- cells determine to a large extent the form of the microscleres. There appear, in short, to be three secondary factors concerned in the production of any particular form of microsclere : (1) the THE PRESIDENT'S ADDRESS. 75 nature of the material (opal) of which the microsclere is com- posed ; (2) the nature of the medium in which it is deposited, viz. the colloidal cytoplasm of the cell ; and (3) the presence of the cell-membrane, by which the growth of the spicule is to some extent restrained and guided. All three are, however, doubtless dependent upon the hereditary constitution of the mother-cell (including, of course, its nucleus), for while the mother-cells in siliceous sponges secrete hydrated silica, those of the Calcarea secrete carbonate of lime, and so on. We have next to inquire how it is that, if the specific forms of sponge microscleres are of no importance to the sponge, such very remarkable forms should ever have arisen in the course of evolution. We have to remember in this connection that we are dealing not merely with a few isolated and unrelated forms, but with progressive evolutionary series along lines as definite as any other lines of evolution with which we are acquainted, and which certainly seem to require some directive force to explain them. If we were dealing with adaptive characters we should at once say that the result was due, as in the case of the megascleres, to the natural selection of small, fortuitous, favour- able variations ; but the fact that the characters in question are, for the most part at any rate, not adaptive, seems, at first sight at any rate, to rule natural selection out altogether. It might be suggested, however, that the solution of the difficulty is to be found in the well-known principle of correlation. In accordance with this idea certain characters of an organism are inseparably linked together with other characters in such a way that any variation in the one must be accompanied by a corresponding variation in the other, though the reason why such characters should be so linked together is often by no means obvious. To upholders of such a view as this the analogy of by-products, upon which I laid so much stress at the beginning of my address, may, I think, prove useful. Although I doubt whether the hypothesis of correlation is adequate to meet the present case completely, it certainly seems worth while to examine it a little more closely. I may illustrate my meaning by reference to the action of a few drops of acid upon an alkaline solution of litmus. Two per- fectly distinct results will be produced. The solution will become acid and it will change from blue to red. You may desire for 76 the president's address. some special purpose to produce one of these results only, but they are inseparably connected and you cannot have one without the other. You cannot have the result aimed at without having also the by-product. Now suppose some change in the constitution of the germ- plasm of an organism to give rise to two modifications in the developing soma or body. We may call the change or modi- fication in the germ-plasm GA and the modifications in the soma SA and Sa. SA and Sa will be inseparably correlated with one another through GA, though — as for example in the case of white tom-cats with blue eyes, which are said to be generally deaf — the connection between them may appear to be quite arbitrary. Suppose further that SA proves to be a useful character and Sa a useless one. Then, under the influence of natural selection, SA will be preserved and may ultimately develop into a very perfect adaptation ; but, if so, GA must also undergo further modification, and this modification will likewise affect Set, which will therefore keep pace, so to speak, with SA. Thus a non-adaptive character (S«) may undergo progressive evolution, which, though in reality indirectly controlled by the action of natural selection, may appear to be guided by some mysterious vital force or entelechy. Now suppose further that as a result of some change in the conditions of life, or merely as the result of its progressive evolution in some particular direction, So- in turn acquires some value in the struggle for existence. Natural selection will, in future, favour its further development directly, and what was at first a mere by-product becomes an adaptive character. Thus adaptive characters may perhaps become linked together in groups, the existence of each group being dependent on some particular property of the germ-plasm through which all the members of the group are connected. At the same time non-aclaptive characters may persist side by side with adaptive ones, and even harmful variations may persist if their injurious effects are counterbalanced by useful characters with which they happen to be correlated and which cannot exist without them. Inasmuch, however, as two useful characters are more valuable than one, natural selection will tend to favour the correlation or linking together of adaptive THE PRESIDENT'S ADDRESS. 77 characters, and this is perhaps the reason why, in the higher organisms, non -adaptive characters are less frequently met with than in lower forms. Moreover, the effect of natural selection will tend to become cumulative and the rate of evolution corres- pondingly increased. It may be objected that even in the highest organisms characters often vary independently of one another, but who knows how many characters are really involved in each such variation ? Moreover, it by no means follows from what has been said above that new characters, whether valuable or otherwise, may not arise singly and remain quite independent of others. In any case the principle of correlation could hardly help us to explain the specific forms assumed by sponge microscleres, or indeed the exact nature of any non-adaptive character ; it could only help to explain why such characters should exist at all and why they should undergo progressive evolution. If it be asked, what are the adaptive characters with which, in our own particular case, the non-adaptive characters of the microscleres are supposed to be correlated ? it must be admitted that this question cannot — at any rate at present — be answered, but it would be sufficient for the general argument if it were granted that a modification in the constitution of the germ -plasm which gives rise to a useful character may at the same time give rise also to a useless one, or perhaps even to many useless ones. The question, why are the specific forms of sponge microscleres what they are1? is probably one that will have to be answered, if it ever is answered, by the chemist and physicist rather than by the mere biologist ; or perhaps by that happy combination of chemist, physicist and biologist whose advent is so much to be desired. I have suggested that the form is probably determined by the hereditary constitution of the mother-cell, including its power to select silica as the raw material to be worked up, but this is no more than to say that the nature of the product turned out by a factory depends upon the character of the work-people employed and of the machinery and raw material with which they have to deal. In the case of our microscleres we want to know a great deal more about the nature of the machinery and the manner in which it is controlled 78 the president's address. before we can hope to reach even an approximate solution of the problem. Some light may perhaps be thrown on the subject by ex- periments such as those of Leduc and others upon artificial osmotic growths. Leduc, in particular, has succeeded in pro- ducing very interesting growth-forms by the osmotic action of various chemical reagents in solution. Some of these forms bear an extraordinary resemblance to the forms of living organisms. I do not, of course, attribute much importance to the particular forms produced in this manner as explaining the particular forms of any living organisms. What they demonstrate is that purely chemical and physical causes may give rise to more or less definite and at the same time non -crystalline forms in colloidal media, and though none of the forms as yet produced come anywhere near our sponge-spicules in symmetry or sharpness of definition, they certainly seem to indicate a hopeful line of inquiry. The particular form produced depends upon the nature of the reagents employed and upon the conditions under which the experiment is carried out. If these always remain constant we may assume that the osmotic growth will always have the same form, but probably with the means at our disposal it would be impossible to produce exactly the same result twice over. The remarkable thing about the sponge microscleres is that within the limits of the same species the same results very often are exactly reproduced, or at any rate so exactly that we are unable to distinguish between them. I suggest that these results are produced by chemical and physical causes, involved in and controlled by the hereditary constitution of the mother-cell, and that any modification of this hereditary constitution must give rise to a corresponding modification in the results. Further than this I fear we cannot at present venture. It has frequently been objected to the theory of natural selection that, however much useful characters may be en- couraged and fostered in the struggle for existence, it cannot account for the first appearance of such characters. This appears to me to be a very fair criticism. It seems to me, also, very misleading to speak of the origin of species by natural selection, for specific characters throughout the animal and vegetable kingdom are, I believe, generally non-adaptive, and therefore cannot be directly due to natural selection. This is certainly the THE PRESIDENT'S ADDRESS. 79 case with the specific characters of sponges, which, as we have seen, depend for the most part upon trivial microscopical differ- ences in the shape of the spicules. Without entering upon the vexed question of the relation between somatogenic and blastogenic characters, we may assume in our ignorance that such characters as those which we have been discussing arise fortuitously in the germ-plasm, and that it is a mere chance whether or not they may prove to be of any value to the organism. If they are valuable, natural selection will foster and encourage them ; if they are not, they may nevertheless persist for many generations unless too injurious to their possessors. If linked by correlation with useful characters they may be indirectly fostered by natural selection, and un- dergo a course of evolution parallel to that of their correlative characters. Although they may be useless at first, they may acquire some special value under new conditions of life, or in the course of their evolution under the old conditions, and then natural selection will begin to act upon them directly.* Possibly all the characters which an organism exhibits, with the important exception of those which are due to the effects of use and disuse of organs, or to the response of the organism in some other way to the direct action of the environ- ment, have first arisen as by-products of the complex chemical and physical processes upon which the life of the organism depends. There is one more aspect of the problem to which I should like * Having been asked to give a definite example of a character which, at first useless, has ultimately acquired an adaptive value, I suggest the pattern of the venation on the front wings, or tegmina, and on the leaf-like outgrowths of the abdomen in the leaf-insect Pulchriphyllium cvurifoliuvi. This venation so closely resembles that of a leaf as greatly to increase the remarkable protective resemblance which undoubtedly enables the insect to conceal itself effectively from its enemies. The mere pattern of the venation in the more primitive and typical Orthoptera can hardly have had any selective value. Of course the venation itself must always have been useful, both for supporting the wings and for supplying them with air, etc. ; but as regards the pattern which the venation makes (which is the character to which I refer) one type of arrangement would seem to have been as good as another until it acquired a special adaptive value as a factor in bringing about protective resemblance to a leaf, and then doubtless the pattern evolved under the influence of natural selection until it reached its present degree of perfection. 80 THE PRESIDENT'S ADDRESS. to direct your attention before concluding. The constancy in the specific form of the microscleres of the Tetraxonida appears to be much greater in the case of the sigmatose than in that of the astrose series, and in the former at any rate seems to point to the different modifications having arisen as mutations rather than as fluctuating variations. This would, I think, be quite in harmony with the views which I have been endeavouring to express. A mutation, however small it may be, is believed to be due to some change, apparently sudden, in the constitution of the germ-plasm, which may then remain without further alteration until another mutation occurs. To say that the change in question is probably of a physico-chemical character seems almost a truism ; but if it is so it seems only natural to suppose that such a modification, transmitted by cell-division to all the mother-cells of a particular kind, may affect in a uniform manner the form of all the microscleres deposited in these mother-cells, just as a change in the character of the reagents employed will affect the form of osmotic growths ex- perimentally produced. If this view be correct, we must suppose also that any adaptive modifications with which the modifications of the microscleres may possibly be correlated must also have arisen as mutations. I see no objection to such a supposition, for mutations, if they occur sufficiently frequently, may be quite as valuable from the point of view of natural selection as small fluctuating variations. We do not, of course, know what may be the cause of the modification in the constitution of the germ-plasm that gives rise to a mutation, but there is some reason to believe that it may be due either to the permutations and combinations of ancestral characters which take place in the maturation and fertilisation of the germ-cells, or to the influence of some change of environ- ment upon the germ- plasm. If the characters of sponge spicules are really of the nature of mutations it should be possible to obtain Mendelian results by hybridisation, and I hope that at some time in the future experiments may be made with this object in view. The difficulties in the way of carrying out such experiments would probably, however, be very great, and we should require to know a great deal more than we do about the breeding habits and life-history of sponges before we could hope to bring them to a successful issue. 33 33 33 3) 33 33 33 THE PRESIDENT'S ADDRESS. 81 Description of Plate 7. Fig. 1. Ideal primitive tetraxon. 2. Plagiotriaene of Ecionema carteri, x 52. 3. Orthotriaene of Pilochrota homelli, X 52. 4. Anatriaene of Tetilla poculifera, X 52. 4a. Cladome of 4 x 230. 5. Protriaene of Tetilla pocidifera, x 52. 5a. Cladome of 5 x 230. 6. Dichotriaene of Ecionema laviniensis, x 52. „ 6a. Cladome of 6, seen from above, x 52. ,, la-Id. Ends of triaenes of Stelletta vestigium, with reduced cladi, x 230. ,, 8. End of oxeote of Stelletta vestigium, x 230. ,, 9. Angulated oxeote of Pachychalina subcylindrica, x 360. „ 10. Straight oxeote of Reniera pigmentifera, x 360. ,, 11. Style of Axinella halichondrioides, x 230. „ 12. Tylostyle of Hymedesmia curvistellifera, X 230. „ 13. Spined tylostyle of Myxilla tenuissima, x 530. ,, 14a-14A. Astrose microscleres of Xenospongia patelliformis, X 530. „ 15. Microxeote microsclere of Desmacella tubidata, x 230. „ 16. Toxiform microsclere of Gellius angulatus var. canalicu- lata, x 230. „ 17a, lib. Sigmata of Gellius angulatus var. canalicidata, x 230. (Note the angulation of the spicule, suggesting derivation from a diactinal microxeote, such as is represented in figs. 26a-26c.) 18a, 186. Toxa of Toxochalina robusta var. ridleyi, X 230. 19. Sigma of Desmacidon reptans, X 512. 20. End of sigma of Paresperella serratohamata, x 530. 21. Diancistron of Vomerula or Hamacantha, x about 200. 22. Isochela of Esperiopsis pulchella, front view, x 284. ,, 22a. Side view of same, x 284. „ 23. Anisochela of Cladorhiza jientacrinus, front view, x 700. ,, 23a. Side view of same, x 700. „ 24. Anisochela of Cladorhiza (?) tridentata, front view, x 360. „ 24a. Side view of same, x 360. Journ. Q. M. C, Series II.— No 72 6 35 33 33 J3 82 the president's address. Fig. 25. Primitive tetraxon (calthrops) of Dercitopsis ceylonica, x 230. „ 26a-26c. Small oxea of Dercitopsis ceylonica, x 230. (Oxea four or five times as large occur in the same sponge.) (Figs. 2-186, 20, 25-26c, from Dendy's Report on the Sponges collected by Prof. Herdman at Ceylon in 1902. Figs. 19, 21, 22, 22a, 24, 24a, from Ridley and Dendy's Report on the Challertgo Monaxonida. Figs. 23, 23a, from Dendy in Ann. <& Mag. Nat. Hist., Ser. 5, vol. 20, PI. xv.) Journ. Quekett Microscopical Club, Ser. 2, Vol. XII., No. 72, April 1913. Journ.dM.C Ser.2yol.XlI Spicules of Tetra-xorud Sponges. 83 ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. By David Bryce. {Read March 2oth, 1913.) Plates 8 & 9. The five species of which descriptions are furnished in the present paper have been known as distinct forms for many years past, although their distinguishing characteristics have not hitherto been gathered into the formal diagnosis which constitutes scientific baptism. Four of them belong to that important section of the Philodinidae in which the food is formed into pellets after passing through the mastax, and are assigned to the genus Habrotrocha. The fifth species belongs to the more numerous section of the same family in which the food is not at any time agglutinated into pellets, and being oviparous and possessed of three toes is a member of the genus Callidina, as now restricted. Under the name of Habrotrocha munda, I describe the form to which T referred in some remarks upon the identity of Callidina elegans Ehrbg., appended to my paper on " A New Classification of the Bdelloid Rotifera," * as having been wrongly identified as that species by Hudson and Gosse and by other writers. I have endeavoured in that place to show as clearly as possible my reasons for the belief that this form cannot be that which Ehren- berg described ; and inasmuch as none of the various correspondents who have addressed me with regard to my classification have advanced a view contrary to my own in this matter, I think that this victim of mistaken identity may now be established on a firmer and less assailable basis. This species is the most common of the few pellet-making forms which have their usual habitat in ponds and ditches. In fresh gatherings it may frequently be seen swimming vigorously with its head slightly deflexed, or perhaps marching about at a great * Jaimi. Q. M. C, Ser. 2, Vol. XI., p. 61. 84 D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. pace, and will often attract attention from the bright reddish colour of the stomach wall. On closer examination it may be readily recognised from the peculiar shape and pose of the spurs, which are quite distinctive, and from the many-toothed rami. Under more natural conditions, it takes shelter in any convenient recess among debris or in leaf axils, and there makes its home, protruding the head and neck when it desires to feed. The second species, Habrotrocha torquata, has similar many- toothed rami, but in several other respects differs distinctly from H. munda. I believe that in some quarters it has also been accepted as Callidina elegans Ehrbg., probably on account of the rami. Unlike H. munda, it is never found in ditches or ponds, but has its habitat usually in mosses growing in positions fre- quently wet. The spurs are of simple form and the stomach wall is never of reddish tint. It has not been observed to seclude itself in any way and is of comparatively quiet habit. Its specific name was suggested by a curious but illusory appearance in some positions of an annulus encircling the expanded corona. The third of the pellet-making species, Habrotrocha spicida, is a " rather smaller form, which has the, so far, unique distinction of a single spine of small size placed on the pre-anal segment on the median dorsal line. When the body is contracted, or when the animal is seen in lateral view, this spine is sufficiently obvious, but at other times it is most easily overlooked. In my own experience this Bdelloid has only occurred in hilly country in elevated positions, but I learn from Mr. James Murray that he has also met with it in lowland habitats. The fourth species, Habrotrocha ligida, is one of those puzzling forms which can only be recognised with certainty when it is feed- ing. It is mainly distinguished by the possession of a small fleshy tooth, which stands erect in front of the narrow sulcus between the two pedicels of the corona, difficult to discern except in direct dorsal view. In other respects it offers little to remark. For my earliest knowledge of the new Callidina, I am indebted to my esteemed correspondent the late Forstmeister L. Bilfinger, D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. 85 of Stuttgart, who sent to me, as long ago as 1894, a sketch of the animal together with some moss in which it occurred. I have therefore given it the specific name Bilfingeri, in honour and in grateful appreciation of a most courteous correspondent and of a painstaking and careful observer of the Rotifera. The type form of this species is marked by a series of lateral and dorsal knob- like prominences on the posterior half of the trunk. As in most other species with such knobs or with spines, the presence of these ornaments is not constant, and occasional examples are found in which some or even all the typical prominences are absent. Habrotrocha munda sp. no v. (PI. 8, fig. 1). Specific Characters. — Corona moderately wide, exceeding collar ; pedicels with dorsal inclination ; discs more strongly inclined in same direction. Under lip relatively high, centrally prominent and spoutlike, Dorsal antenna long. Rami with seven or more fine teeth. First foot joint with dorsal prominence. Spurs resembling caudal processes of Chaetonotus. In general build and in the somewhat " smothered " appearance of the corona, due in this case to the shortness of the pedicels and to the very oblique setting upon them of the trochal discs, this species has a certain resemblance to Habrotrocha torquata, but can usually be distinguished from it by the shape of the spurs, which in typical specimens have a very characteristic moulding and pose. In the normal or extended position, the body is spindle- shaped, distinctly larger about or a little behind the centre, and smaller at either extremity, and rarely exceeds 320 /x in length. While the rostrum is shorter and thicker than usual, the head and neck are only moderately stout, the trunk being distinctly larger (sometimes almost swollen when well fed), the lumbar segments short and tapering rapidly to a relatively small and slender foot of (I think) three segments. When creeping, the dorsal and lateral longitudinal skin-folds are usually well marked. In adult examples the stomach wall is frequently of a vivid reddish colour, and the lumen of the stomach is usually crammed 86 D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. with obvious food pellets. The first foot segment has a median dorsal prominence of moderate height, rather wider than long, and best seen in lateral view. The second segment has the very- characteristic spurs, which always suggest to me the caudal processes of the common form of Chaetonotus. They are longer than is customary among pellet-making species, frequently measuring 14 to 15 /x in length, but are sometimes much shorter. Near the base they are swollen on the inner side, and closely approximate. About mid-length they suddenly diminish in thickness and are thence produced to rather acute points. The outer side of each is nearly straight, and they are held at a slightly divergent angle. The three toes are difficult to see, but the terminal pair (and I think the dorsal toe" as well) are moderately long and acute. The dorsal antenna is sometimes quite 25 fx long and is carried much as in Rotifer macrocerost being inclined backwards when the animal is creeping about, and directed more or less forward when it is feeding. The corona attains a width of about 45 li. The trochal discs are separated by a shallow furrow, which narrows to a mere notch as it nears the ventral side. On that side accordingly the principal wreath is almost uninterrupted, and in place of the customary appearance in front view of two distinct " wheels '' there is rather that of a toothed band passing rapidly round a. single transversely elliptic course, distinctly broken on the dorsal side and only slightly indented on the ventral. In lateral view it is seen that the pedicels are dorsally inclined, short and obliquely truncate, so that the trochal discs are still more inclined towards the dorsal side. The under lip and mouth margins are high in relation to the discs, and the former centrally prominent and spout-like as in Habrotrocha angusticollis, but in a lesser degree. The upper lip is usually hidden by the reverted rostrum. So far as I have been able to discern, it rises moderately towards the centre and is neither bilobed nor reflexed. The rami are about 19 fx in length, somewhat triangular in outline, and have each at least seven very fine teeth. D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. 87 Habrotrocha munda occurs most frequently in pools, especially when water-mosses and anacharis are present. I have also found it occasionally in sphagnum and in confervae, both in floating masses and in the growth upon submerged stones. In suitable situations it makes for itself a rough case or nest of the same type as that produced by Rotifer macroceros. It is of cosmopolitan distribution. I have noted it for England, Scotland, Germany (Baden, Black Forest, Wurtemberg, Stuttgart), Cape Colony. Habrotrocha torquata sp. nov. (PL 8, fig. 2). Specific Characters. — Of medium size and stoutness. Corona equal to or rather exceeding collar ; pedicels short, distinct ; trochal discs more or less dorsally inclined. Upper lip moderately high, undivided but centrally slightly reflexed ; under lip unusually high, yet scarcely prominent. Dorsal antenna rather long. Kami with six or more fine teeth. Spurs short, divergent, conical. When creeping about, H. torquata is somewhat difficult to recognise, as it lacks any conspicuous peculiarities of form, colour or size. It is perhaps most usefully described by comparison with other species of the same genus having similar many-toothed rami. The body is of moderate dimensions, less spindle-shaped than in H. munda, but less parallel-sided than in H. elegans (Milne). The rather short foot is longer and more distinct than in the latter species, but is less so than in H. constricta (Duj.). The spurs are simple short cones of moderate stoutness, and are held at almost a right angle, differing thus from the slighter and widely divergent spurs of H. constricta, the short, peg-like, very slightly divergent spurs of H. elegans (Milne) and the com- paratively long moulded spurs of H. munda. In most examples the stomach is not obviously tinted, but is occasionally of a yellowish colour, yet never of the reddish shade frequent in H. munda, H. auricidata, and other species. In habit it resembles H. constricta ; that is to say, it lives in the 88 D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. open and is not a dweller in the shelter afforded by natural or contrived gatherings of dirt particles or debris like H. elegans (Milne) and H. munda. I have never met with it in pools, but usually in mosses (not sphagnum) growing in wet positions. When the corona is displayed, it is seen to have a quite unusual appearance. As in H. munda, the trochal discs are inclined towards the dorsal side, but in a varying degree, and are separated by a furrow deeper than in that species. The upper lip rises in a broad rounded lobe which is centrally bent back, leaving visible the fleshy connection, or nexus, between the short pedicels. On the ventral side the under lip rises unusually high, and thus in dorsal view, the collar, which passes round the pedicels on either side and merges gradually into the under lip, has an obliquely upward direction, not obliquely downward as customary. This results in the optical presentments of the rapidly beating cilia of the secondary wreath (those lining the collar and passing round to the mouth), and of the cilia of the principal wreath (those of the trochal discs), being to some extent commingled, and there is the appearance of an annulus or ring passing round the trochal discs immediately below their margins. When the discs are seen so that their planes are nearly coincident with the line of sight, they appear to have deeply grooved margins, but the exact appearance varies with the angle at which they are viewed. Whether the appearance be that of a ring or of discs with deeply grooved margins, it is in my opinion purely an optical effect arising from the mutual interference of the light rays from the two wreaths of cilia. The high under lip is unusually flat and inconspicuous ; the lateral margins of the mouth are scarcely thickened and the mouth cavity is small as compared with that of other Philo- dinidae. When feeding the lumbar plicae are well marked. The foot represents about one-ninth of the total length. It has four joints, the first having dorsally a distinct thickening of the hypodermis. In the confinement of a small cell H. torquata proved only D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. 89 moderately hardy. After a few days, most specimens would feed freely under the unaccustomed light and would remain quiet, but I have never known eggs to be laid under such conditions. By no means a common species, yet widely distributed ; I noted it first in moss sent me in 1895 by Forstmeister L. Bilfinger, of Stuttgart. I have since found it in moss from Epping Forest, Essex ; Chagford, Devon ; Pass of Leny, Perthshire ; Black Forest, Baden. Dimensions. — Greatest length 410 fx, more frequently 320 to 350 fx. Corona 38 to 41 /x. Kami about 15 fx. Spurs 6 to 9 /x. Habrotrocha spicula sp. nov. (PI. 9, fig. 1). Specific Characters. — A single, short, blunt spine, sub-erect upon dorsal median line of pre-anal segment. Corona small, 13-18 [x wide; pedicels adnate; upper lip high, rounded, un- divided. Rami with four teeth each. Spurs, short cones, widely separated. A rather small species, chiefly noteworthy for the solitary spine and its unusual position. No other Bdelloid yet known has only a single spine or has spines only upon the pre-anal segment as in this case. When the animal is in its most retracted position, as one usually sees it lying inert among moss debris, the spine stands out distinctly at the hinder end of the body, and it is also well shown when the animal is feeding and assumes the squatting position natural to many species. It is easily overlooked when the animal is crawling about unless a good side-view is presented. It springs from a thickened base, and is rather blunt, short and slightly bent. When seen from the front the very small corona is nearly circular in outline, the trochal discs being separated by a shallow furrow and the pedicels adnate. In dorsal view the high rounded upper lip rises quite to the level of the trochal discs, and its apex indeed is visible in ventral view. The margins of the mouth have small angular lateral prominences, which are partly 90 D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. visible even from the dorsal side and add to the apparent width of the collar. When extended the body is moderately stout and the longi- tudinal skin-folds are well marked. In most cases it is colourless, but examples of a faintly reddish colour have been seen. The antenna is short, but rather stout. The rami are small, 14-15 tt long. The foot tapers rapidly and is very short. In the feeding position it is usually hidden beneath the trunk. It seems un- suited for crawling on a smooth surface such as glass, as the animals have unusual difficulty in getting foothold. The first joint has frequently a strong protuberance on its dorsal side. The spurs are very small cones about 3 /x long separated by an interspace about 6 /x wide. The largest examples measured were about 200 jx long when extended, but others were from 170 to 185 /x. My earliest speci- mens were found in mosses collected for me on Cader Idris by Mr. D. J. Scourfield in 1895. Others came from collections on Mickle Fell and on Snowdon by the same friend. In 1898 I found it in moss from the top of Ben Ledi, in 1907 from the top of Ben Vrackie, both in Perthshire ; and in 1906 from tree- moss in the woods above Triberg in the Black Forest, Baden. It has also been found repeatedly by Mr. James Murray in Scotland and in many foreign habitats. Distribution : cosmopolitan, mostly at high elevations. Habitat : ground, rock or tree-mosses. Habrotrocha ligula sp. nov. (PI. 9, fig. 2). Specific Characters. — Moderately slender. Corona somewhat wider than collar ; pedicels rather high, semi-adnate ; discs separated by narrow sulcus. Upper lip rising very slightly and displaying a small fleshy tooth, which near its apex tapers suddenly to a point. Rami with four teeth each. Foot three- jointed ; spurs small, tapering cones with interspace nearly equal to their length. D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. 91 A species of rather less than medium size which in its extended position offers no obvious character for its recognition. The rostrum is short and stout, and the dorsal surface has a distinct almost ridge-like thickening of the hypodermis, best seen in lateral view. Its movements are active when crawling about, and when feeding it sways and bends almost incessantly in all directions, the body being well extended and the upper foot joints visible. The trochal discs are rather small and the greatest width of the corona little exceeds that of the collar. The pedicels are adnate to nearly half their height and are very slightly divergent. At the dorsal end of the nexus between them is a small fleshy ligule or tooth, which for the most part is nearly cylindrical, but near the tip tapers rather suddenly to a point. It is so inconspicuous that it can rarely be seen except in direct dorsal view and when the animal keeps steady for a brief interval. Even then the exact shape of the ligule is difficult to determine, but I think that it differs somewhat from the type of ligule possessed by any of the few Bdelloids in which this peculiar ornament or organ has been seen. In Habrotrocha eremita (Bryce), in which it was first noted, it is a simple, short, peg-like tooth, very slender and tapering gradually, and, to judge from the figures given by Murray, it appears to be of the same character in Habrotrocha acornis Murray and Callidina lepida Murray. In the present species the appearance is rather that of a fleshy cylindrical pedestal, with a tapering point inset at the end of the pedestal as if in a socket. The upper lip rises in a low curve about as high as the base of the ligule. The rami have four teeth, but one tooth on each is much less prominent than the others. I have noticed that the food pellets are rather small. Examples isolated produced eggs of oval outline, hyaline, smooth-shelled, measuring 70 /x at the longest by 43 //, at the shortest diameter. I had this species first in 1894 from a roadside near Deal, and in the following year from a wall in Bognor ; in both cases from small button-like tufts of wTall-moss. I did not see it again until 92 D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. some few weeks ago, when it was brought to me by Mr. G. K. Dunstall, who had obtained it from moss collected near Leith Hill, in Surrey. It is probably a more common species than these three isolated records would indicate. It may be that it has a partiality for small tufts of moss (which do not invite examination), or perhaps its restlessness and the absence of any very obvious peculiarity when marching about has led to its being overlooked. In view of Murray's opinion that the presence of a ligule in Bdelloids is an unsafe specific character, as it often appears in species where it is not normally present, it must be pointed out that, while it may be presumed that the ligule in Habrotrocha ligula is fairly constant, it is by no means impossible that examples should occur in which it might be absent, and in that case, if normal specimens were not available for comparison, identification might well be difficult. Dimensions. — Length about 320 fx. Corona 30 /x. Collar 25 /a. Ramus 1 7 /x. Spurs 5 ll. Callidina Bilfingeri sp. nov. (PI. 9, fig. 3). Specific Characters. — Of medium size, and moderately stout, posterior trunk having a series of knob-like prominences. Trochal discs well separated, but corona not exceeding collar width. Upper lip rather high and wide, with shallow central depression. Rami with two teeth each. Dorsal antenna short, about half the neck thickness. Foot three- jointed; first joint laterally swollen, second very short, somewhat distended to form sucker-like disc. Spurs very minute cones, with wide, slightly convex interspace. So far as I am aware, this rather well-marked species, of moderately stout build and medium size, has been met with only in ground-mosses. Typical specimens are easily recognised from the series of knob-like prominences which ornament the sides of the trunk segments and the dorsal surface of the rump segments. D. BRYCE ON FIVE NEW SPECIES OF BDELLOID R0TIFER4. 93 The number of these "knobs" appears to be very inconstant, as in sketches made by Forstmeister Bil finger, James Murray, and myself it varies from eleven to five ; and I was informed by the first-named correspondent that he had met with examples without any knobs at all. In such cases the species can still be determined with moderate certainty from the peculiar structure of the second foot joint, and the minuteness and wide separation of the spurs. When the full number of prominences are present they are distributed thus : the third segment of the trunk (or central portion of the body) has one at either side, close to its anterior boundary ; the same segment and the fourth and the sixth have each one at either side near their posterior boundaries; while on the dorsal side of the fifth and sixth segments there are three more, arranged in a triangle (two in front on the fifth and one behind on the sixth segment, the latter on the median line). The fifth segment is moderately swollen laterally. The lateral knobs on the sixth segment (the anal) are more nearly constant than the others. Those most frequently absent are the anterior pair of the third segment. The first foot joint has distinct lateral swellings, and is per- haps swollen dorsally as well. The second joint is very short, and slightly distended with thickened skin, forming a sucker- like disc from the lower surface of which the three short, broad toes are protrusible. The flange-like hinder margin of this foot disc forms the slightly convex interspace between two very minute spurs. When creeping about the animal is seen to have a short and stout rostrum. In the feeding position the body is somewhat flattened, and the dorsal longitudinal skin-folds are obliterated. The trochal discs are well separated, but the head is stout and the corona does not exceed the collar width. The upper lip rises rather widely and high, and has a shallow central depression. The rami are 14 to 16 ^t long, and are widest above the middle. The anterior outer margin of each is distinctly thickened, and passes gradually into a delicate winglike expansion of the ramus. 94 D. BRYCE ON FIVE NEW SPECIES OF BDELLOID ROTIFERA. As already stated, this species was first discovered by the late Forstmeister L. Bilfinger in the vicinity of Stuttgart, and notified to me in 1894. It was afterwards found by Mr. George Western, probably near London, and in 1904 by James Murray, near Fort Augustus. In 1906 I met with it in moss gathered on the bank -of a roadside ditch near Triberg, in the Black Forest. Quite recently numerous examples have been found in moss collected by Mr. G. K. Dunstall near Leith Hill, Surrey. Dimensions. — Length about 315 /a. Corona 38 /x. Collar 41 /a. Spurs 1 to 2 /a (on inner edge). i Description of Plates 8 and 9. Plate 8. Fig. 1. Habrotrocha munda sp. nov., extended, dorsal view, x 350 ; la, head and neck, corona displayed, in lateral view, X 650 ; lb, the same, in ventral view, x 750 ; lc, mouth, in front view (diagrammatic). „ 2. Habrotrocha torquata sp. nov. In feeding position, corona displayed, dorsal view, x 550 ; 2a, spurs, x 1600. Plate 9. Fig. 1. Habrotroclut spicula sp. nov. In feeding position, corona displayed, ventral view, x 600 ; la, retracted position, X 600 ; 16, foot extended, dorsal view, x 800 ; lc, ramus, X1600. ,, 2. Habrotrocha ligula sp. nov. In feeding position, corona displayed, dorsal view, x 480. ,, 3. Callidina Bilfingeri sp. nov. In feeding position, dorsal view, x 350; 3a, ramus, x 1600. Journ. Quekett Microscopical Club, Ser. 2, Vol. XII., No. 72, April 1913. Joum.QM.C. Ser. 2.Vol.XH,P1.8. i \ r / - 8 Ifn ( ■ I Aft f i fr""M'. '*? ' 11/ 1 4 la. 2. HBryce AelacLnat. lb. AH.Searle.lith. New Species of Bdelioid Rotifera. Journ. Q.M.C. Ser2.Vol.Xn,P1.9. - ■ \© i la. i - h m * f \i ■ "J I ■\(\. ..-.,V-. p /■•■! V ! I u lb. 2. F=^ lc. 3a AHSearie. New Species o£ Bdelloid Rotifera. 95 NOTES. A NEW LOW-POWER CONDENSER By Edward M. Nelson, F.R.M.S. {Read November 26th, 1912.) The condensers which at present are supplied with microscopes are only suitable for low powers ranging from | inch upwards. With powers lower than these a difficulty arises, for it is not possible to fill the field with the image of the source of light focused upon the object, as it should be. Substage condensers suitable for low powers are all too short in focus, consequently the image of the source of light is far too small. In these circumstances microscopists have been, and are, accustomed to waive critical illumination and employ the most uncritical of all illumination, viz. to focus the image of the source of light upon the front lens of the objective ; this is nothing more nor less than lantern illumination, which gives a critical image of a diaphragm limiting the field, but of nothing else ; all delicate lines and structures are coated with black diffraction borders. The obstacle in the way of using a long-focus condenser is that there is not sufficient room to focus it. Powell's No. 1 stand has a good deal of room, but not enough, and other microscopes are simply nowhere. Now the way this difficulty may be surmounted is to construct the condenser upon the telephoto principle. This has now been done, and Messrs. Baker will show you this evening a substage condenser they have made from my design which has 4 inches of focal length and requires only 1 inch of working distance. With this condenser the image of the fiat of the flame bears the same relation to a 4-inch objective with the large field of a P. & L. No. 1 A eye- piece, as the image with one of the ordinary universal condensers, with the top off, does to a | inch ; and this is precisely what was wanted. Now let us understand exactly what this means. A 4-inch objective has a focal length of 2| inches; with a No. 1 A eyepiece the size of the object on the stage that is embraced 96 E. M. NELSON ON MICROSCOPE CONSTRUCTION in a field of view is —$ inch, therefore it is necessary for the condenser to focus upon the stage an image of the flat of the flame ■—$ of an inch wide. The condenser has a low aperture of N.A. 0*14, but large enough for the objectives for which it is intended to be used. NAVICULA RHOMBOIDES AND ALLIED FORMS.* (Addendum.) By Edward M. Nelson, F.R.M.S. {Bead November 2M7i, 1912.) With reference to the question, " What was the Amician Test?" quite accidentally I recently came across a notice to the effect that the test used by the Jurors at the International Exhibition (London, 1862) was the Navicula ?'homboides under the name of JV. affinis. This of course clears up all the difficulty. This N. rhomboides would have been of the kind termed the " English " rhomboides in my paper, and would have had 72 to 73 striae in 0*001 inch. ON MICROSCOPE CONSTRUCTION AND THE SIDE SCREW FINE ADJUSTMENT. By Edward M. Nelson, F.R.M.S. (Bead November 26th, 1912.) There is one point which has been overlooked with respect to the evolution of the microscope. It is thought that the modern plan of placing the coarse adjustment slide and the body upon the fine adjustment was the invention of Zentmayer (1876), and that it first appeared in this country in the Ross-Zen t may er model. This however is not the case, for Powell in 1841 invented this plan, as well as that of the side pinion fine adjustment, now so much in vogue. In the frontispiece of Cooper's Microscopiccd Joumcd an illus- tration of this model will be found, f Some years ago Mr. T. * Journal Q.M.C., Ser. 2. vol. ii. p. 93. f This was the first microscope Powell introduced after Lealand had joined the firm (vide Journal B.M.S., 1900, p. 287, fig. 78). AND THE SIDE SCREW FINE ADJUSTMENT. 97 Powell kindly showed me one of these microscopes, but it had escaped my memory. The coarse adjustment was by rack and pinion ; this was not attached to the limb by a slide, but by a kind of cradle. This cradle was pressed down by a spring on to a horizontal cone, which was moved by a horizontal fine- adjustment screw, which had a milled head on each side of the limb. The importance of this model should be recognised by every one who uses a microscope, for not only was it the first microscope to have a side screw, but also it was the first instrument in which we find the limb attached to the foot on two upright pillars. This double support to the joint (now almost universally used) was the invention of George Jackson (President R.M.S. 1852-3). Before this all microscopes that were capable of being inclined were attached to the foot by a single upright post and a compass joint.* Powell attached the two pillars to a flat tripod base by a swivel so that the base could be placed in such a position as to give the greatest amount of stability however much the body might be inclined (some makers in copying this arrangement graduated this arc of rotation !). Ross copied this kind of joint in the model he brought out in 1843, but substituted two parallel flat plates for the two pillars ; but Messrs. Smith and Beck adopted the two-pillar form in their 1846 model. This microscope of Powell's had a Turrell stage, a micrometer stage, an achromatic condenser, Nicol polarising and analysing prisms ; so it was in its day an instrument of a very advanced type. In 1843 Powell & Lealand discarded the two pillars for the gipsy tripod, which is the best form of foot ever designed.f Coming now to modern times, horizontal fine adjustments may be placed in two groups, viz. (a) those with continuous motion and (b) those without. The drawback which those of the first kind possess is that the user does not know whether he is focusing up or down ; and the drawback which all the second kind, excepting the Berger, have is that of damage and injury to the delicate moving parts when they butt up against a stop. The Berger avoids all risk of damage from this source by causing * Some ancient non-achromatic microscopes had ball and socket joints, but those early forms are not now under discussion, t For fig. see Journal R.M.S., 1900, p. 289, fig. 79 Journ. Q. M. C, Series II.— No. 72 7 98 E. M. NELSON ON MICROSCOPE CONSTRUCTION. an idle nut to butt against a stop ; if this nut receives damage or- strain to its thread it is of no importance. The first kind adopt a continuous motion in order to secure immunity from this danger, and put up with the great disadvantage of having a fine adjustment which does not follow the direction of the movement of the milled head. The following simple device has been designed to effectually prevent any damage taking place. To the right hand side of the limb, where the micrometer drum-head is placed, a short piece of tube, threaded on the outside, is fixed, and through it the fine adjustment pinion passes just like the cannon pinion in a clock. Fig. 1. Fig. 2. An idle nut works on this screw in a slot inside the micrometer drum. It is then arranged that this nut will permit ten rotations of the fine-adjustment pinion to be made, and then stop further motion by butting either against the side of the limb or against the end of the inside of the micrometer drum. Figs. 1 and 2 will make this simple device clear without further explanation. NOTE ON PLEUROSIGMA ANGULATUM. By Edward M. Nelson, F.R.M.S. {Read January 28th, 1913.) About the end of the eighties I took a photomicrograph of a specimen of Pleurosigma angulation, which had been broken in a very remarkable manner so that it was possible to demon- E. M. NELSON ON V LEU RO SIGMA AStiULATUM. 99 strate the existence of two membranes. At one part the upper membrane had been torn away leaving the lower membrane, at another the lower membrane had gone while the upper was left, the rest of the valve having both membranes in position. These three photomicrographs of the upper, lower and both membranes were exhibited to the Club. No other specimen I have seen has been so fortunately fractured as to demonstrate both membranes so clearly as this one. The network in one membrane differs slightly from that of the other, so that after a little practice one is able to state whether the membrane under observation is an upper or lower membrane. The upper membrane in P. strigosum resembles the diamond panes of a leaded light, while the lower is like wire netting, fig. 3. In P. balticum and allied forms the upper memb^ine has slit-like apertures in longitudinal rows, while III O-go Fig. 3. Fig. 4. the lower membrane has circular apertures, fig. 4, where the circular apertures in the lower membrane are seen through the intercostal silex of the upper membrane and in a line with the bars between the slits. Now at that time it was thought, and probably it is still the received opinion, that the lower membrane " eye-spotted " the upper membrane ; by which is meant that the apertures in the lower membrane are directly below those in the upper membrane — much in the same way as in Coscinodiscus the eye- spot is directly below the perforated cap at the top of the cell. Recently, however, study on P. angidatum with a Leitz apo- chromat, y1^ inch of 1*40 N.A., has caused me to change my opinion, for the apertures in the lower membrane can be un- mistakably seen below the intercostals of the upper membrane, and this is true not only of P. angidatum, but also of all allied forms that have been examined. No mention has been made of Mr. T. F. Smith's observation. 100 E. M. NELSON ON PLEUROSIGMA ANGULATUM. on the structure of the genus Pleurosigma, because this note, not being an exposition of the structure of this genus, deals merely with the single fact of my altered opinion with regard to the apertures in the lower membrane not " eye-spotting " those in the upper. The genus Pleurosigma has been seventy years before the microscopical world, not laid aside, but worked at continuously by the most skilful microscopists, yet all the problems con- nected with their structure have not been solved. It is only by recording from time to time a little bit here and a little bit there, and by putting these little bits together, that complete and accurate knowledge of this difficult subject will be attained. ACTINOCYCLUS RALFSII AND A COLOURED COMA. By E. M. Nelson, F.R.M.S. {Read January 28th, 1913.) The following account of a microscopical phenomenon, never previously observed, may be of interest. When working on a mixed diatom gathering, dry and un- covered, with a Powell & Lealand | inch and a lieberkuhn, there appeared round an Actinocyclus Ralfsii a wide border of brilliant orange, green and blue light. The inside of the valve was uppermost and the bottom of the cup was in focus, so that the surrounding mist was caused by the out-of -focus edge, which, of course, was at a higher level. Any one seeing this coloured mist would have exclaimed what a badly corrected objective ! but if they had looked at the other diatoms in the field, they would have seen that the out-of -focus coma was white ! The colour, then, must be a function of the Actinocyclus. Another objective with a lieberkuhn, viz. a Powell & Lealand T4^ inch, was tried on the same diatom ; the border was now red, the green and blue having gone ! A third objective, viz. a Wenham | inch with lieberkuhn (really a T4