60 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL. 



(gastro- vascular system of Polyps, so-called vessels of Medusae and 

 Ctenophora). The so-called stomach of the Anthozoa is simply an 

 invagination of the body wall into the central cavity of the animal, 

 and functions only as oesophagus. 



When a distinct alimentary canal is present, the chyle is absorbed 

 by the walls of the gut, and passed through them into the coelom or 

 space developed between the gut and body walls (into the general 



D 



Br 



FIG. 51. Daphiiia with simple heart. C, the slit -like opening on one side is seen; D, 

 alimentary canal; L, liver; A, anus- G, brain; O, eye; Sd, shell gland; Br, brood 

 pouch placed dorsally beneath the carapace. 



tissue of the body in the acoelomate parenchymatous worms), and 

 there gives rise to a fluid, the blood, in which (with some few 

 exceptions) corpuscles (cellular structures produced in the organism) 

 are found. In this space, or in a system of lacuna? derived from it, 

 the blood circulates. Primitively its movements are quite irregular, 

 taking place with each movement of the body (as in many worms), 

 and are effected chiefly by the contractions of the somatic muscles 



