54 ORGANIZATION AND DEVELOPMENT OF ANIMALS IN GENERAL . 



in the simplest cases, as in the Amoebae and Rhizopodn, by prolon- 

 gations of the sarcode (pseudopodia) surrounding the foreign body 

 (fig. 41). In the Infusoria, which are covered by a firm cuticle, 

 there is a central semi-fluid mass of sarcode (endoplasm), which is 

 distinct from the more compact peripheral layer of sarcode (ecto- 

 plasm), and which receives the nutrient substances through the 

 mouth and digests them. 

 Rows of larger cilia are 

 pre&ent, which serve the 

 purpose of procuring food 

 (adoral ciliated zone of the 

 Ciliata) (fig. 42). 



Fio. 42. Stylonychia mytilns 

 (after Stein) viewed from the 

 ventral surface ; Wz, adoral 

 zone of cilia; C, contractile 

 vacuole; N, nucleus; A T/ ,nucle- 

 olus (paranucleus); A, anus. 



r 6 



FIG. 43. Longitudinal section through the 

 body of an Anthozooid (Octactinia). 

 M, stomachic tube with the mouth open- 

 ing in the centre of the feather-like tenta- 

 cles ; Jiff, mesenteric folds ; G, genital 

 organs. 



Among the animals with cellular differentiation (Metazoa), the 

 internal cavity of the body in the Crelenterata (morphologically 

 identical with the alimentary cavity and not with the body cavity 

 of other animals) functions as a digestive cavity, and its peripheral 

 adially arranged portions as a system of vascular canals (gastro- 



