Miscellaneous. 521 



forms Neomenia, Proneomenia, and Chcetoderma gave a strong im- 

 pulse to this idea on account of their similarity' in some respects to 

 what obtains in the Polyplacophora ; but it is not safe to argue a 

 direct descent from these forms, or even to imagine that thej^ come 

 into the ancestral line at all. It is quite possible that they and the 

 Polyplacophora are offshoots from the direct stem, and probably we 

 must look more to the embryological history of the Gasteropods for 

 light on the subject. Attempts have been made, notably by Hat- 

 schek (' Studien ii. Entwickelungsgesch. d. Anneliden,' Wien, 1878), 

 to trace a relationship between the Polyrforclms-laicYa of the Anne- 

 lida and the MoUuscan larva, and thus to throw any relationship 

 which may exist between the two groups back to a very early period 

 in their evolution. 



If it can be shown that there is considerable similarity between 

 the larvae of the two groups, and if the differences which do exist 

 can be explained as adaptations to new conditions, the presumption 

 as to the genetic relations between the larvae will be greatly 

 strengthened. As regards the arrangement of the cilia, which is 

 the only point to be dealt with in this note, we have in the Poly- 

 gordius-larya a strong preeoral locomotive band, a more delicate 

 postoral nutritive band, and a still less apparent ciliated region lying 

 between these two bands and leading into the ciliated mouth. The 

 identity of the cilia of the velum of the Gasteropod larva with the 

 first of these has been frequently noticed ; they form a strong prae - 

 oral band, occasionally double, and differing from the band of the 

 Polygordius-larya only in the extent of its development, and in its 

 incomplete closure in manjr cases dorsally. This latter point of 

 difference does not, however, hold throughout ; the former may be 

 explained by the necessity for a more powerful locomotive apparatus 

 than is required for the Annelida, caused by the presence of a shell, 

 a structure which appears very early in the life-history of the Mol- 

 lusca. A postoral band has never as yet been described for the 

 Prosobranchs. Several observ^ers have called attention to the pre- 

 sence of a single band of cilia behind the cilia of the velum, and 

 have regarded it as mitritive in function, and the object of this note 

 is to call attention to the fact that this band passes across the ventral 

 surface of the larva behind the mouth, and is therefore quite com- 

 parable to the postoral band of the Trochophore. My attention was 

 first called to this fact in the larvai of Crepidida fornicata, and I 

 was afterwards able to confirm it in those of Fulgar carka, in a 

 species of Neptunea, in two Prosobranch Veligers as yet undeter- 

 mined, and in the Opisthobranch Montaguia, sp. ? In the undeter- 

 mined Veligers the velum was produced into four long flattened 

 arms, round the margins of which were the strong locomotor cilia. 

 On the under surface of the arms, running parallel to and not very 

 remote from the locomotor cOia, was the finer band of nutritive 

 cilia, the transparency of the arms and their size rendering it very 

 apparent, and it could without much difficulty be traced across the 

 ventral surface of the body immediately behind the mouth. Dr. W'. 

 K. Brooks informs me that he noticed the existence of this postoral 

 band some time ago, and was then inclined to attribute some phylo- 



