162 BIOLOGY. [BOOK n. 



In the sea-urchins and the holothuria there are a mouth, teeth, 

 jaws, a distinct intestine, an anus. 1 



In the grand class of the arthropods (crustaceans, arachnida, 

 myriapods, insects), there exists a digestive apparatus regularly 

 and definitively constituted. (Fig. 8). Often, especially in 

 the crustaceans and the insects, the intestinal epithelium 

 is clothed with a hard layer of chitin, sometimes emitting 

 projections destined to crush the aliments. In the crus- 

 taceans, certain anterior parts become buccal pieces. The 

 glandular system is enriched and diversified. The crustaceans 

 have a voluminous liver, full of a yellow-greenish bitter juice. 

 This liver decomposes into ramose cylinders. 2 Most insects have 

 also cesophagian glands tubulated, enrolled, lobated, ramified, 

 and which are supposed to be salivary. Other glands forming 

 simple or ramified tubular sacs, debouch into the median in-j 

 testine ; it is conjectured' that they represent the liver of the 

 superior animals. In insects, the secretion has still a mis- 

 cellaneous character. In the long slender and flexuous tubes, 

 which are usually inserted at two distinct points of the intestine, 

 and which are called the vessels of Malpighi, there is secreted by 

 the side of the urine, another matter probably of a bilious 

 nature. The yellowish canals are believed to represent the; 

 biliary canals. 3 



In many arthropods we already remark that the alimentation 

 considerably influences both the form and the dimension of the 

 digestive apparatus. Carnivorous animals have a digestive 

 apparatus conspicuously and comparatively short. The larva of 

 the butterfly, which makes an enormous consumption of aliments, 

 has a very wide intestine, while the butterfly itself, which eats 

 little, and only liquid aliments, has a long and slender digestive 

 tube. 



Certain insects (bombyx, ephemerides, oastri), which are very 

 voracious in the state of larvae, are, in the adult state, destitute 



, Physiologic Compares. 2 Dugks, loc. tit. 



* Leyd.ig,Histologie Comparee, p. 336. Duges, loc. tit., t. III. p. 400. 



