76 Natural History of Molluscous- Animals ; — 



brought forward to supply its place ; but, that there may be 

 no deficiency in its length, we find the apex soft and vascular, 

 where, in fact, a continual growth and addition are going on. 

 (Cuvier, Mem. sur la Pa telle, p. 18.) 



The food taken hold of first by the lips, and then divided 

 by the jaws, is immediately seized by the prickles of the 

 tongue, which prevent its regurgitating, while the actions of 

 the adjacent muscles force it into the gullet ; on the sides of 

 which there is a pair of lobulated salivary glands, or some- 

 times two pairs, which have each a single excretory duct to 

 convey their peculiar secretion into its upper part, to lubricate 

 and soften the mass. The gullet is a muscular canal, lined 

 interiorly with a mucous coat, presenting, indeed, the same 

 structure as the whole alimentary canal, and is generally 

 plaited in a longitudinal direction. But the variety exhibited 

 in the form, structure, and disposition of the stomach and 

 intestines is too great to permit us to attempt a general view. 

 The former is sometimes merely a membranous bag, or simple 

 dilatation ; sometimes there is a gizzard, analogous to the 

 gizzard of birds *, to triturate the food previously to its trans- 

 mission into this bag ; sometimes there is a series of dilata- 

 tions, or stomachs, three or four; and, again, in others we 

 find the gizzard, or stomach, armed with horny teeth, or 

 laminae, of which the Scyllae x a affords a remarkable instance. 

 (Cuv. Mem., p. 10. tab. 1. fig. 6.) " There is no division of the 

 alimentary canal into small and large intestines, as in the 

 higher classes ; or rather, among the Mollusca, the relative 

 size of the different parts is reversed. Here the pyloric ex- 

 tremity is usually the largest, while the anal is more slender." 

 (Fleming, Phil. Zool., ii. 411.) The intestine is usually a 

 simple canal, which, after making a volution or two among 

 the lobes of the liver, returns upon itself, and opens outwardly 

 on the side towards the anterior part of the body ; but, in 

 Doris, the anus is pierced on the back towards the tail ; and 

 we find, in Chiton and Dentalium, other exceptions to the 

 usual course; for, in them, the intestine is straight, and has 

 a posterior terminal aperture, like the annulose tribes. To 

 show to what extent the alimentary canal is varied in this 

 tribe, let me give you a representation of that of the Tethys 

 (Jig. 7.)? which you will compare with that of Pleurobran- 



* Of the stomach of Limneus Swammerdam says, " it is of the same 

 structure, in all respects, with that of the hen or cock kind ; so that one 

 would think the real stomach of a hen is here represented, without any 

 difference, but that it is much smaller." 



