Oct. 12, 1888.] 



SCIENTIFIC NEWS. 



39i 



Reports of the Scientific Results of the Exploring Voyage of 

 H.M.S. "Challenger." Prepared under the direction 

 of the late Sir Wyville Thomson, F.R.S., and now 

 of Mr. Jno. Murray. Vol. xxiii. : Zoology. I. and 

 II. : Reports on Pteropoda (part ii., Thecosomata; and 

 part iii., Anatomy), by Paul Pelseneer, D.Sc. 

 III. : Report on Hydroida, by Prof. G. J. Allman, 

 M.D., LL.D., F.R.S.S. L. and E., etc. 

 The above reports on the curious minute molluscs, 

 scientifically known as Pteropoda, but from their shape 

 and movements more popularly termed " winged 

 snails" and "sea butterflies," form the second and third 

 memoirs which Dr. Pelseneer has contributed on this 

 subject to the Challenger series, he having dealt with the 

 Gymnosomata, i.e., those Pteropoda which in the adult 

 state have neither a shell nor mantle skirt, in a previous 

 volume (" Zool. Chall. Exped.," part Iviii.). In the first 

 report in the present volume the author gives a full 

 systematic description of the other great division of the 

 Pteropoda — the Thecosomata — which in the adult condi- 

 tion possess both shell and mantle. This memoir and 

 the following one are based on a very extensive set of 

 specimens, including, besides the Challenger's spoil, those 

 collected by the Triton, by Mr. Rattray in the Buccaneer, 

 and by the Italian Ve/tor Pisani in its three years' scien- 

 tific cruise, as well as collections made at Malta by 

 Surgeon D. Bruce, M.B., and by Dr. Pelseneer himself 

 at Naples, a wealth of material rarely available, and of 

 which the writer has rendered ample account. It seems 

 at first sight rather curious to learn that although the 

 Challenger specimens were taken from seventy different 

 stations in all parts of the world, and included shells 

 dredged from the deposits of " Pteropod ooze," only one 

 form worthy of anew name was discovered. This ceases, 

 however, to be very remarkable when we find that only 

 forty-two species of Thecosomata exist ; indeed, the really 

 striking thing is this small number of species, for the 

 Pteropoda not only occur in all the great seas from Arctic 

 to Antarctic regions, but they swarm to such a prodigious 

 degree that, though of very minute size, they often 

 actually colour the surface of the water for several square 

 miles in the Arctic seas, where they are said to form an 

 important part of the food supply of the Greenland 

 whale. 



The Thecosomata, as looked at from the general stu- 

 dent's point of view, have left Dr. Pelseneer's hands in a 

 greatly simplified condition — out of a previously possible 

 thirty-four genera he has abolished all but eight, while 

 among the species the slaughter of names has of course 

 been proportionately heavy. Thus the fourteen species 

 of Clio recognised by Dr. Pelseneer, have hitherto rejoiced 

 in six generic and fifty-seven specific designations, and 

 his genus Cavolinia of eight species represents four genera 

 and fifty-four species under old systems of classification. 

 This is indeed something to be thankful for. 



The second report (part iii.), which deals with the 

 structure and classification of the Pteropoda, will be of 

 much wider interest than the two previous memoirs. 

 In it the author discusses the comparative anatomy of 

 each genus of both the great Pteropod divisions in as far 

 as the main organs have in his opinion either been 

 hitherto imperfectly understood, or are calculated to 

 throw light on the affinities and systematic position of the 

 group. This part of the work seems to have been 

 carried out with great thoroughness, and, as might be 



be expected, involves many differences of opinion and 

 corrections, as well as confirmations of the work of his 

 predecessors, Souleyer,Van Beneden, Huxley, Fol, Gegen- 

 baur, and others. What may be called the battle of the 

 ganglia is fought at great length, and the partial twisting 

 of the body, on which the proof of affinity to other groups 

 of Mollusca so much depends, receives its share of atten- 

 tion. Perhaps, however, the reasoning in these two 

 questions would have been more readily followed if one 

 or two additional illustrative diagrams or drawings had 

 been introduced. The conclusions of Dr. Pelseneer from 

 these studies are that the Pteropoda are not a branch of 

 the cuttlefish group or Cephalopoda, nor are they a class 

 (of equal value with the latter) of the Mollusca, both of 

 which views have prevailed and still prevail among 

 zoologists, but that they are a subordinate branch of the 

 Gastropoda or snail-like Molluscs. This itself is enough 

 to cause a mild surprise, but we are positively startled to 

 learn that the two divisions of Pteropoda themselves are 

 not at all related to one another as Pteropoda, but that al- 

 though both are derived from Tectibranchiate Gastropoda, 

 the Thecosomata spring from a family of which Bulla may 

 be taken as the type, while the Gymnosomata originate 

 from a not very distant family represented by Aplysia, 

 the "sea-hare," the modifications in their form arising 

 from the adoption of a life on the high seas remote from 

 land and the consequent necessity of habits of continual 

 swimming. 



The Pteropods are thus not a primitive group which 

 has existed without much change from remote periods, 

 but a recent and terminal one. They certainly possess 

 the following characteristics of terminal groups quoted 

 from Prof. Giard. (1) They are profoundly modified 

 in adaptation to a special mode of existence. (2) They 

 exhibit very slight variability. (3) They include a very 

 small number of species. If, however, the Pteropoda are 

 a recently developed group, it may be asked what be- 

 comes of Theca, Conularia, Cleodora, Tentaculites, and 

 other Palaeozoic and secondary fossils hitherto classed as 

 Pteropods. The answer is short. Dr. Pelseneer ejects 

 them all from the group without hesitation, and recog- 

 nises no fossil Pteropoda below the Tertiary. In this he 

 is probably right, and on the conchologist and palaeonto- 

 logist, who appear equally to lack his esteem, will devolve 

 the task of finding a new home for the outcasts. It should 

 be mentioned that, as Dr. Pelseneer points out, De Blain- 

 ville was the first to show the near relationship of the 

 Pteropoda to the Gastropoda, and that his views have 

 been since supported by Souleyet, Spengel, Grobben, and 

 Boas. As no classification can now be accepted which 

 lacks the aid of embryology, it is to be hoped that this 

 test will shortly be applied to the views so ably expounded 

 by Dr. Pelseneer. It is, perhaps, worth pointing out that 

 on page 88, fourteenth line from the top, the perplexing 

 word " Aplysoidea " is evidently a misprint for " Thecoso- 

 mata." 



III. The Report of Prof. Allman on the Hydroida deals 

 with the Tubularinae, Corymorphinae, Campanular nas, 

 Sertularinae, and Thalamophora ; the Plumularinae and 

 Hydrocorallinae having been already described, the 

 former by Prof. Allman and the latter by Prof. Moseley 

 ("Zool. Chall. Exp.," part vii.). It is divided into two parts, 

 the first being a complete " Exposition of Hydroid Mor- 

 phology from the standpoint of our present knowledge," 

 and the second a description of the various genera and 

 species collected in the expedition. Thirty-nine splendid 

 plates drawn by the author and Miss M. M'Daniel, a map 



