346 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



ach as a permanent organ. Food touching the body any- 

 where is ingulfed. The semifluid protoplasm flows around 



it, takes it in, and digests it. 

 Whatever is indigestible is 

 thrown out again, and the di- 

 gested part at once appropri- 



Fig. 233. — Paramcecum. The ar- 

 rows show the course of the food 

 until discharged. 



Fig. 234. — Amcebaproteus:/A, food 

 bodies ; cv, contractile vesicle ; 

 >:, nucleus. (After Leidy.J 



ated and assimilated (Fig. 234) ; see also Fig. 156, page 

 240). These lowest animals have neither tissues nor 

 organs of any kind, but extemporize these as wanted — 

 whether locomotive organs, prehensile organs, mouth, 

 or stomach. 



It is from such low beginnings that, it is believed, all 

 the types of animal structure have been gradually differ- 

 entiated by a process of evolution through all geological 

 times. 



