resemblance with Gastropoda greater and in consequence did not think it necessary to bring 

 Clio to a separate order. Yet, this was done by him two years afterwards ^). And on his great 

 authority only, later investigators accepted his division. 



The "ordre des Ptéropodes" remained, and the only modification, made by Cuvier himself 

 afterwards'), was that the "orders" of Cuvier were now called "classes". That the notion of 

 "class, order" etc. was not yet fully comprehended, is illustrated by the following fact : in 1810 

 Péron and Lesueur, who have the same opinion as Cuvier with respect to the systematic 

 treatment, speak of the "familie des Ptéropodes" in their article : Histoire de la familie des 

 Mollusques Ptéropodes. Ann. Mus. d'Hist. Nat. Paris 18 10. Vol. XV, p. 71. 



That the Pteropoda constitute a separate class among the Mollusca has long been a 

 prevalent opinion and is perhaps so still. It would be going too far, to mention the names of 

 all those who have stuck to this opinion. 



Of the zoologists of later time, some of whom have at least made studies of their own 

 about the organisation of the Pteropoda, the best known are : 



LOVÉN (1848), TrOSCHEL (1848), OWEN (1S55), BURMEISTER (1856), WoODWARD (1856), 



Keferstein (1866), ScHMARDA (1872), voN Ihering (i8;6), Huxley (1877), Gegenbaur (1878), 

 Claus (1882). 



In this respect we must not overlook the fact that Gegenbaur ^) brought Gastropoda, 

 Pteropoda and Heteropoda all to one class, viz. the Cephalophora ("Gastropoda im weiteren 

 Sinne"), maintained this opinion in his "Vergleichende Anatomie", and then changed his mind so 

 much afterwards. On the other hand. Claus regards the Pteropoda as an order of the Gastropoda 

 in his third edition of his "Lehrbuch der Zoölogie" p. 574 (1885). And voN Ihering, who in 

 1876^) emphatically pointed to the conformity of the two classes: Pteropoda and Cephalopoda 

 has changed his opinion afterwards ^), at least with respect to the pretended resemblance. 



The general conviction is that the Pteropoda are nearest related to the Cephalopoda. 

 This opinion, maintained by many zoologists so persistently, was principally founded on the 

 resemblance of the head-appendages of the Gymnosomata and the arms of the Cephalopods. 



Some have even gone so far that they regarded the Pteropoda as an order of the 

 Cephalopoda. This idea, first pronounced by Oken °), was held afterwards by Ray Lankester '), 

 who divided the class Cephalopoda in two groujas : 



a. Pteropoda and h. Siphonopoda (= Cephalopoda s. str.). 



It was in 1821 that de Blainville pointed out the many points of resemblance which 

 the Pteropoda had with the Gastropoda "). It was his opinion that the Bulloidea were the 



1) Sur l'Hyale. Sur un nouveau genre de Mollusques nus (Ie Pneumodermon) et sur rétablissement d'un nouvel ordre de 

 Mollusques (les Ptéropodes). Ann. Mus. d'Hist. Nat. Paris, Vol. IV, p. 232. 



2) Règne animal. Paris 181 7, Vol. II. p. 378. 



3) Gegenbaur. Untersuchungen über Pteropoden und Heteropoden. Leipzig 1855, p. 189. 



4) ^'^''gl- Anatomie des Nervensystems und Phylogenie der MoUusken. 1876, p. 272. 



5) Zeitschr. Wissenschaftl. Zool. 1881, Bd. 35, p. 4. Über die Verwandschaftsbeziehungen der Cephalopoden. 



6) Lehrbuch der Zoölogie. Bd. I, p. 326. 



7) Encyclopaedia Britannica. g'h Ed. Vol. XVI, 1883. 



8) Dict. des sciences naturelles. Prt. XXII, p. 66. 



