182 BIOLOGY. [Book ir. 



Nevertheless, at very different degrees of the zoological 

 hierarchy the same mode of alimentation seems to bring with it 

 the same structure. Thus the internal surface in certain carni- 

 vorous coleoptera, for instance the stag-beetle, has a reticulated 

 aspect wholly analogous to that of the stomach of the mammifers. 

 It is true that we have here to deal with a superior invertebrate 

 in which the vitality is active, energetic, and the digestive system 

 strongly differentiated. 



Some other facts come to prove the feeble digestive power of 

 the stomach in the inferior invertebrates. Trembley observed 

 that the hydra neither altered nor digested one of its arms when 

 it swallowed it along with a prey. The actinia devoured by a 

 larger individual of its own species is often revomited safe and 

 sound. It therefore resists digestion as the entozoa resist. 

 The fact is not, however, general ; and frequently shell 

 moUnsks, and whole crustaceans, swallowed by the actinise and 

 the asterise are completely digested excepting the shells or 

 the carapace, which are afterwards rejected. 



The facts of resistance opposed to digestion by certain 

 living animals are evidently due to the defect of energy in the 

 digestive liquids secreted, that is to say, to the imperfection of the 

 glandular system. Among the mammifers things go on dif- 

 ferently, and thoroughly living tissues are promptly attacked 

 and digested by the stomachal secretion unless they are pro- 

 tected by a thick epidermic or epithelial varnish. Claude 

 Bernard having. introduced into the stomach of a dog, through 

 a gastric fistula, the posterior portion of a frog, saw that 

 portion dissolved and digested, while the anterior portion con- 

 tinued to live. , 



The agent of this curious dissolution is a very active juice 

 secreted by the stomachal glandules, and of which we have 

 now to speak. 



When the aliments are introduced into the stomachal cavity 

 of a mammifer the mucous membrane is congested, grows red, 

 and we see streaming out, when there is a gastric fistula, as in 



