20 Mr. H. J. Carter on the SpermatoJogij of a neiv species o/Nais. 



adult mollusk is enclosed between two irregular-shaped valves, 

 like an Ethei'ia, with the tube and the valves of the young shell 

 on the produced end of the attached valve. (See Proc. Zool. 

 Soc.) 



In Humphreyiay on the contrary, the small united valv'es 

 are attached by their ventral edge, and they are extended be- 

 hind into a free, ascending, subquadrangular tube, like Ver- 

 metus, which continues to grow in length as the animal increases 

 in size. 



The use of the tubules in Aspergillum and Clavagella, and of 

 the minute perforations in the lower part of the tube of the 

 genera Furcella and Foegia, has not been satisfactorily explained. 

 They have been supposed to admit water to the front part of the 

 body of the animal, and have been regarded simply as tubes 

 or perforations, as if they were always open ; but they can only 

 be formed round the tentacles, and it is most probable that the 

 tentacles fill up the tubular cavity during the life of the animal, 

 though they are vacant, and the tentacles on which they have been 

 formed are not to be observed in the specimens of the animal 

 which are preserved in spirits. The admission of water to the 

 front of the animal does not appear to be necessary for their 

 (Economy, as such tubules or pores are not to be found in the 

 tubes of Teredo, Gastrochcuna, &c. In some ClavageUce and 

 Aspergilla, the tentacles and the tubules which cover them are 

 branched and spread out, as if the mollusk wished to obtain a 

 knowledge of the animals and other bodies in its neighbourhood. 

 They may also serve to steady the tubes, as roots do trees, 

 and prevent their being thrown down by the usual waves of the 

 sea, as it is the kinds which live sunk a small depth in the sand 

 that apj)ear to have the tubules most extended ; while those that 

 are sunk deeper, or are fixed on rock, have only jjcrforations in 

 their place, — as trees which have their roots near the surface 

 have them greatly extended horizontally. 



It is to be observed, that when these animals have completed 

 their tube, if they extend any more in size, it is only posteriorly 

 in the length of their siphons ; and then they extend the length 

 of the shell by tlie addition of fresh portions to the siphonal end 

 of the tube, as shown by the ruffles in IVarnea and Bryopa. 



IV. — On the Spermatology of a new species ©/"Nais. 

 By H. J. Carter, Esq., H.C.S. Bombay, 



[With three Plates.] 



The following communication contains a description of the de- 

 velopment of the spermatozoa in the ovisac with the ovum, in a 



I 



