AND PHYSIOLOGY. 



199 



consisting of a more or less pedunculated thin walled vesicle, 

 which is multiplicated on itself when empty. The second 

 portion consists of a stomach (ventriculus) in which the chyle 

 is formed, and which is continuous at the point of insertion 

 of the malpighian vessels with the third portion of the digest- 

 ive canal. This third portion commences by a small and usu- 

 ally short ileum, which is followed by a colon larger and of 

 variable length. This last often has a caecum at its anterior 

 extremity, and terminates posteriorly in a short, muscular 

 Rectum/' 



"A considerable number of insects take no food during 

 their perfect state, the object of their existence being only to 

 accomplish the act of reproduction. Their jaws are often 

 very rudimentary, and are fit neither for sucking nor for 

 masticating." 



361. The Annelida have sometimes quite complicated 

 jaws, even as many as eight or nine, moving laterally. They 

 have also salivary and hepatic glands, as have many other 

 invertebrates. These are shown on Fig. 197, which repre- 

 sents the whole alimentary canal of an insect. 



362. The Cephalopod Molluscs have a mouth, two horny 

 jaws moving vertically in the pharynx, a tongue, an oeso- 

 phagus f a stomach, a pylorus, and an intestinal canal. 



363. In the Cephalophora the jaws move laterally for the 

 most part. In the whole class we find a biliary apparatus 

 and generally salivary glands. Fig. 201 shows the digestive 

 organs of a Gasteropod, the Aplysia. Nearly all the Ceph- 

 alophora have a longer or shorter fleshy mass attached to 

 the base of the pharynx that is comparable to a tongue. It 

 has a longitudinal grove in it, and is sometimes included in a 

 sheath. It is always covered with horny denticulated plates 

 and spines, which are very delicate, and arranged in quite 

 elegant longitudinal and transverse rows. The points of these 

 spines turn backward, which aids greatly in swallowing. 



