THE 



VOYAGE OF H.M.S. CHALLENGER 



ZOOLOGY. 



REPORT on the Pteropoda collected by H.M.S. Challenger during the 

 Years 1873-76. By Paul Pelseneer, D.Sc. (Brussels). 



PART I.-The GYMNOSOMATA. 



INTRODUCTION. 



1. History of the Group. 



It is now more than two hundred years since a Gymnosomatous Pteropod was first 

 described and figured; 1 but it was only at the beginning of this century that the. 

 organisation of these animals was investigated, and the group Pteropoda established. 2 



As to the subdivision Gymnosomata, its establishment is of a still later date. Peron 

 and Lesueur, who considered the Pteropoda to form a much larger group than they 

 really do, 3 divided these animals into two subgroups : — (l) those without shells; (2) those 

 with shells 4 — and it has been found that this division, established on the very empirical 

 character of the presence or the absence of a shell, is quite justified by the anatomical 

 differences, as will be seen further on. 



Nevertheless, the majority of zoologists continued for a long time to divide the 

 Pteropoda into non-natural groups. Thus, Cuvier 5 distinguished those forms with 



1 Clime limacina, in 1676, by Martens, Spitzbergisehe oder gronlandische Reisebeschreibung, p. 169, pi. P. fig./. 



2 By Cuvier, in 1804 (Memoire sur l'Hyale et le Pneumoderme ; Ann. Mus. Hist. Nat. Paris, t. iv. p. 232), and 

 not in 1798, as noticed by Bronn (Die Klassen unci Ordnungen des Thierreichs, Bd. iii. p. 584). 



3 They embraced, in fact, Opisthobranchia (Phyllirhoe, Glaucus), Heteropoda {Carinaria, Firola), and even 

 Ctenophora {Callianira). 



4 Histoire de la famille des Mollusques Ptiropodes; Ann. Mus. Hist. Nat. Paris, t. xv. p. 57, 1810. 

 6 Le Regne animal, ed. 1, 1817. 



(zool. chaix. exp. — part lviii. — 1887.) Mmm 1 



