Chap, x.] DIGESTIVE APPAKATUS IN THE ANIMAL SEKIES. 163 



of organs of manduoation. WloUy destined for generation, they 

 cannot take any nutriment] hence the brief duration of their 

 life.i 



J£ we except the hrachyopods, whose intestine terminates in an 

 imperforated caecum, the mollushs have a very complete digestive 

 system, and comparable, in a certain measure, with that of the 

 vertebrates. In the cephalopods, we find a long cesophagus, an 

 enlarged stomach, an intestine with circimivolutions, and a 

 rectimi. In the littorine we observe an arrangement of the 

 stomach, which exists in certain vertebrates ; there are a cardiac 

 part and a pyloric part, separated by a salient fold. Sometimes 

 the stomach is furnished with triturating booklets of varied 

 form. But it is especially by the development of the glandular 

 appendices that the stomach of the moUusks is distinguished 

 from that of the animals hierarchically inferior. These organs, 

 in efiect, go on perfecting and complicating themselves more and 

 more in the diverse families of mollusks, and especially in the 

 most advanced of the mollusks, the aquatic cephalopods (Cuvier), 

 there are oesophagian salivary glands with short caecums, a liver 

 developed, compact, divided into lobes, provided each of them 

 with an excretory conduit, and all these conduits open together 

 or separately at the origin of the median intestine, or into the 

 stomach. The liver of the mollusks functionates essentially 

 like that of the vertebrates. That gland is in this class very 

 voluminous, and it fabricates sugar at the expense of the blood 

 though in the mollusks this liquid is destitute of globules. 



From the point of view of the general form of the digestive 

 tube, properly so called, the vertebrates have signal fellowship 

 with the mollusks. However in them the degree of organic 

 specialisation is more elevated still. Thus the buccal cavity 

 which is not divided in fishes and the amphibians, commences in 

 reptiles to be sectionised into two divisions, a nasal or aerian 

 division and a buccal or digestive division. 



Corneous teeth, analogous to the appendices of the same kind 

 ^ Diiges, Pkysiologie Compmrie, p. 279. 



M 2 



