58 
THE VOYAGE OF H.M.S. CHALLENGER. 
2A. But it is in the second group of interpretations of the systematic position of the 
Pteropoda — that is to say, among those which place them along with some other 
Molluscan class — that we find the idea of their connection with the Cephalopoda carried 
to the furthest extreme. This view consists in regarding the Pteropoda as Cephalopoda, 
and in simply ranking them within this group. It was long since defended by Oken 1 
and by Eschscholtz. 2 More recently it has been adopted by Ray Lankester. 3 * 
2B. We now come to the third hypothesis, according to which the Pteropoda should 
be placed among the Gastropoda. 
In this connection it is interesting to point out that Cuvier, who established the 
“ class” Pteropoda, remarked in his memoir on Clio borealis 4 that this animal exhibits 
“ aucun des caracteres des Cephalopodes,” but that on the contrary it “ offre beaucoup 
de rapports avec les Gasteropodes.” In 1800, in his Legons d’anatomie comparee, he even 
placed Clio ( = Clione) among the Gastropoda, which, however, did not prevent him four 
years later from creating a distinct class for the Pteropoda. 
It must be noted, however, that certain important points in the morphology of the 
Pteropoda were incompletely understood by Cuvier; thus he misunderstood the foot 
(that is the median part of the foot) of the Gymnosomata. This organ was compre- 
hended only by de Blainville, wdio with remarkable insight affirmed that the relations of 
the Pteropoda were with the Opisthobranchia (“ Bulleens ”), at the same time reducing 
the group Pteropoda to its proper rank, and abstracting from it the foreign forms 
(Heteropoda, Nudibranchia, Coelenterata) which had been introduced by Peron and 
Lesueur, with the exception of Phylliroe , 5 
I must admit, however, that the two hypotheses which I have placed in the second 
main group have not had very favourable receptions. I have already stated that Oken’s 
interpretation, that the Pteropoda are Cephalopoda, is only defended at the present day 
by Ray Lankester. De Blainville’s interpretation, that the Pteropods are Gastropods 
nearly related to the Bulloidea, which was so ably defended by the lamented Souleyet, 6 
who died in 1852, has also fallen into oblivion. 
Spengel, however, in his study of the nervous system of the Mollusca, places the 
Pteropoda among the Euthyneurous Gastropoda, as a group of the same rank as 
the Opisthobranchia and Pulmonata, 7 though still with a certain amount of reser- 
vation. 8 
1 Lehrbuch der Zoologie. 2 Zoologischer Atlas. 
3 Mollusca, Encyclopaedia Britannica, 9th ed., vol. xvi. 4 Ann. Mus. Hist. Nat. Paris, 1802. 
6 It was Souleyet and not Leuckart who first recognised the true affinities of Phylliroe. His work dates from 1846 
(Com pies rendus, t. xxii. p. 473), whilst that of Leuckart was only published in 1851 ( Archiv f. Naturgesch., Jahrg. xvii. 
P-139). 
0 Voyage de la Bonite, Zoologie, t. ii., 1852. 
7 Die Geruchsorgane und das Nervensy stern der Mollusken, Zeitschr. f. wiss. Zool., Bd. xxxv. p. 373. 
8 Ibid., p. 381. 
