206 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



In the myriapods and larvae the same general plan is continued, the 



alimentary canal still being a simple tube passing from one extremity 



of the body to the other, with an oral orifice and vent, but in these 



animals showing a division into gullet, stomach, and intestines (Fig. 62). 



A difference is also met with according as the animals are carnivorous or 



vegetable-feeders. In the former the canal is narrow and nearly straight, 



with a slight dilatation representing the stomach, 



while in the herbivorous species it is complicated 



by saccular pouches to delay the onward progress 



of the food. In the tunicata the division of the 



alimentary canal into gullet, stomach, and intestines 



is more marked, since we have in them a distinct 



oesophagus, stomach, small and large intestines. In 



the crustaceans there exists a definite digestive 



apparatus, with the first appearance of distinct 



glands having for their function the secretion of 



digestive juices, crustaceans especially having a 



voluminous liver which secretes a yellowish-green 



fluid of the nature of bile. In the crustaceans 

 -cg 



OES 



Fig. 59. — Diagram of 

 the Alimentary Ca- 

 nal of an Earth- 

 worm, after Ray 

 Lankester. 



M, mouth; PH. pharynx; 

 OES, oesophagus ; CG, calcare- 

 ous glands : CP, crop ; G, giz- 

 zard ; I, intestine. 



Fig. 60— Transverse Section of Earth-Worm to Show 

 position and Relations of the Intestines, after 

 Claparede. {Jeffrey-Bell.) 



A, cuticle ; B. hypodermis ; C. layer of circular muscles ; D. layer of longitudinal 

 muscles ; I, enteric cavity ; M, "green layer ; " N, dorsal vessel ; O, liver. 



the liver has become a symmetrical, lobulated organ, instead of the 

 numerous small folliculi which are found in 'earlier forms around the 

 alimentary canal, and which pours its secretion into the upper part of 

 the intestine. In the higher crustaceans, such as the crabs and lobsters, 

 there is a short, wide sac, provided with internal hard, calcareous dent: 

 icles, which serves the purpose of a gullet, stomach, and iiizzard. The 



