354 Animal Biology 



Respiration. — Oxygen is taken in from the water through the body 

 surface. Carbon dioxide passes out through the body surface as well as 

 through the contractile vacuoles. 



Excretion and Egestion. — A large contractile vacuole is usually located 

 near each end of the body. Each contractile vacuole has radiating canals 





f-j^ 



PARAMOECIJM 

 PREPARING FOR FISSION 



FISSION COMPLETED 



Fig. 169. — Paramecium reproducing by asexual, binary fission (transverse divi- 

 sion), shown diagrammatically. Note the division of the nuclei, gullet, and con- 

 tractile vacuoles. (From Parker and Clarke: Introduction to Animal Biology, 

 The C. V. Mosby Co.) 



t^"7trl l^ba-g'i. 



rid. tri. fi: 





(»«^^ 



•■'■A 



B 



Fig. 170. — Structure of the ectoplasm of typical Protozoa of the class Infusoria. 

 A, Frontonia leucas (cross section) ; B, Paramecium sp. (cross section) ; C, Para- 

 mecium sp. (surface v^iew) ; pel., pellicle; cor., cortex; tri., trichocyst; enp., endo- 

 plasm; fl., cilium; ha. gr., basal granule (microsome) at the base of each cilium; 

 alv., alveolar layer of minute regular vacuole; rid., surface ridges of the pellicle; 

 fi' ., point of insertion of cilium in the middle of each hexagonal area; hexagonal 

 areas are formed by the striations of the pellicle. (From Borradaile and Potts: 

 The Invertebrata. By permission of The Macmillan Company and the Cambridge 

 University Press, publishers.) 



