NA TURK 



337 



THURSDAY, AUGUST 9, 1! 



THE ZOOLOGICAL RESULTS OF THE 

 "CHALLENGER" EXPEDITION. 



Report on the Scientific Results of the Voyage of H.M.S. 

 " Challenger" during the Years 1873-76, under the 

 command of Captain George S. Nares, R.N., F.R.S., 

 and the late Captain Frank T. Thomson, R.N Pre- 

 pared under the superintendence of the late Sir C. 

 Wyville Thomson, Knt., F.R.S., and now of John 

 Murray, one of the Naturalists of the Expedition. 

 Zoology— Vols. XXI 1 1., XXIV., and XXV. (Published 

 by Order of Her Majesty's Government, 1888.) 



THE first two memoirs in Vol. XXI 1 1, are Reports on the 

 Pteropoda by Dr. Paul Pelseneer. Dr. Pelseneer's 

 Report on the Gymnosomatous division of the Pteropods 

 was published in Vol. XIX., and we now have his Report 

 on the Thecosomata and one on the anatomy of the 

 whole group. 



In the first of these Reports all the certainly genuine 

 species at present described are enumerated, and full 

 details are given about all those which have been more 

 or less imperfectly described. As the diagnoses of the 

 families and genera of the Pteropods seem to have been 

 copied from originals of a comparatively early date and 

 without modification, it has been necessary on re-study 

 to re-write these, so as to bring them up to the level of 

 scientific accuracy. This monographic study of the sub- 

 group of the Thecosomata has been based not only on 

 the collections made by the Challenger, but on those 

 in the British and Brussels Museums, as well as those of 

 several private collections. Like the Gymnosomata, these 

 Thecosomata are pelagic Mollusks, .which descend to 

 certain depths to avoid too bright a light, and reascend 

 to the surface of the water when the light is feeble or 

 absent, and when the sea is calm. With a less highly 

 organized alimentary system than the Gymnosomata, the 

 Thecosomata content themselves with humble prey, 

 feeding mainly on Radiolaria, Foraminifera, Infusoria, and 

 even on some of the lower Algal forms. 



The Thecosomata were taken alive at seventy different 

 stations, and while they include twenty-eight species, 

 representing all the known genera, they have all been 

 already described. Of those dredged from the deep sea, 

 where " Pteropod ooze" was found, some twenty- four 

 species could be distinguished, of which one was new to 

 science. The total number of Thecosomata now known 

 amounts to forty-two. 



While the generic titles given to living forms amount 

 to thirty-four, these can well be included, according to 

 the author, in the following eight : — 



Cavolinia, Abildgaard. 

 Cymbulia, Peron and Lesueur. 

 Cymbuliopsis, gen. nov. 

 Gleba, Forskal. 



In an appendix to the account of the species of the first 

 two of these genera, some account is given of the forms 

 described by A. Adams as Agadina stimpsoni, and A. 

 gouldi, which are proved to be Gastropod larvae. 



Shells of Thecosomata have not been found in a greater 

 Vol. xxxviii.— No. 980. 



Limacina, Cuvier. 

 Peraclis, Forbes. 

 Clio, Linn. 

 Cuvierina, Boas. 



depth than 1950 fathoms. Mr. J. Murray attributes this 

 to the greater proportion of carbon dioxide in the water 

 at greater depths, and to the more rapid solution of the 

 delicate shells in sea-water under great pressure. 



The third part of Dr. Pelseneer's Report treats of the 

 anatomy of the whole of the Pteropods. With it this 

 Report is now the most comprehensive treatise in exist- 

 ence on the group. As a result of his studies he regards 

 the Pteropods as forming not a primitive group, but, on 

 the contrary, a recent and specialized one — a terminal 

 group. There are in it but a small number of species ; 

 these exhibit only a slight variability, and they are pro- 

 foundly modified in adaptation to a special mode of 

 existence. 



Since the days of Cuvier the Pteropoda have been re- 

 garded as forming a distinct class among the Mollusca, 

 of the same value as the Cephalopoda, Gastropoda, &c. ; 

 but Dr. Pelseneer regards it as proved that they are but 

 Gastropods, in which the adaptation to pelagic life has so 

 modified their external characters as to give them an 

 apparent symmetry ; that even among the Gastropods they 

 do not constitute a distinct sub-class, nor even an order, 

 that they belong to the Euthyneura, and among these to the 

 Pectibranchiate Opisthobranchs, differing less from these 

 than they differ from the other Opisthobranchs. The 

 Thecosomata and Gymnosomata are two independent 

 groups, not having a common origin, the former having 

 descended from the Bulloidea, and the latter from the 

 Aplysioidea. 



These Reports are illustrated with seven plates. 

 The third Report in this volume is by Prof. G. J. All- 

 man, forming the second part of his memoir on the 

 Hydroida. The author has taken advantage of the 

 opportunity afforded by the typical character of the col- 

 lection to make it the basis of a general exposition of 

 Hydroid morphology, and this from the present stand- 

 point of our knowledge, so that this Report is not a mere 

 mass of descriptive and distributional details, but one 

 which will have an abiding interest for the biologist. 



The rare occurrence in the collection of British species 

 is striking, and would seem to indicate a peculiar definite- 

 ness in the geographical distribution of the Hydroids. 



The few Gymnoblastic Hydroids in the collection belong 

 to three genera — Stylactis, Eudendrium, and Monocau- 

 los ; the species (M. imperator), by which the last genus 

 is represented, being perhaps the most remarkable Hy- 

 droid obtained during the Expedition. The stem, though 

 only half an inch in thickness, was 7 feet in height, the 

 hydranth extending, from tip to tip of the tentacles, to a 

 width of 9 inches, so that, as regards size, all other 

 Hydroids sink into insignificance when compared to it ; 

 while the depth of about 4 statute miles from which it 

 was brought up adds to the special interest of this 

 marvellous animal. 



The families of the Calyptoblastea were numerously 

 represented in the collection, and among those of which 

 few examples had hitherto been known are those to 

 which belong the genera Cryptolaria and Grammaria, as 

 well as a new and interesting genus, Perisiphonia. Idia, 

 hitherto only known by the poor description and figure of 

 Lamouroux, proved, on the examination of good speci- 

 mens of the only species, /. pristis, Lamx., to be con- 

 structed on a type quite unique among the Hydroida. 



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