ox THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA 1/5 



Xatica and Sigaretus. In both these genera it shows a tendency to 

 invest the head. In the Cephalopoda, the anterior arms, which must 

 be considered as the propodium, fairly unite in front of the mouth, and 

 it seems ver\' possible that the cephalic hood of Gasteropteron, the 

 " oral " tentacles of Aplysia, the hood of Tethys, the " lips " of some 

 Pteropoda, and the hood of Pneuinodermon may be the result of a 

 similar change. But all attempts to settle these points, save by de- 

 \-elopment, must be more or less hypothetical.^ 



To this same test of development we must refer everything which 

 claims to be called " mantle',' a word which has perhaps been more 

 vaguely and loosely used than any other term in zoology. Surely if a 

 term is to have an)- value in either zoological or anatomical nomen- 

 clature it must be applied to only a defined thing. The " mantles " of 

 a Sepia, a Cleodora, or a Buccinuin may be homologous with one 

 another, but they certainly are not so with what is called the 

 ■' mantle " in Doris or any other Xudibranch.^ The simple fact 

 that the cephalic tentacles arise in the midst of the so-called " mantle " 

 of the latter, is sufficient evidence to show that it cannot be homologous 

 with the " mantle " of the former. The so-called " margins of the 

 cloak " in these genera appear to me to have much more relation to 

 the epipodium. 



Cuvier allows a mantle to Doris, but denies it to Glaucus and 

 Eolidia ; why, is not obvious. 



Leuckart defines a mantle to be " a scutellate (schildformig) dupli- 

 cature of the outer integument extending from the neck for a var\'ing 

 distance backwards." By this definition, however, the upper surface 

 of the anterior division of a Bulla would be a " mantle," which it is 

 not, since the true mantle is obviously behind separated from this b\' 



1 In the absence of any knowledge of development perhaps the source of the nervous 

 supply is one of the best tests of the real homology of a part. llr. Hancock, in his valuable 

 paper "Upon the Olfactory Apparatus in the Bullids" (Annals of Nat. Hist., March, 

 1852), has, I observe, applied this test to the cephalic expansion of the BtcUidie, to the hood 

 of Gasteropteron, &c. ; and since it clearly appears that these parts are supplied by ner\-es 

 from the cephalic ganglia, which never give branches to any portion of the foot, the sug- 

 gestion in the text must be given up. 



- Leuckart, believing the hoemal tegument of the Xudibranchiata to represent a mantle, 

 suggests that there is a difference between their "gills" and those of other moUusks, which 

 as he justly observes, are never processes of the mantle, he. cit. p. 130. The argument in 

 the text tends to show, that in this respect there is in reality no difference between the 

 "gills" of the Nudibranchiata and those of other moUusks., On other grounds, however, I 

 am inclined to think that Leuckart's distinction is a. just one. The organs called gills in 

 the Xudibranchiata appear to me to be in all cases what they undoubtedly are in Eolis, viz., 

 gastro-hepatic appendages. Even in Doris, where they are gill-like, they are supplied with 

 hepatic blood only. See Hancock and Embleton's admirable, memoir " On the Anatomy of 

 Doris," Philosophical Transactions, 1852. 



