THE HIGHER ORGANISMS 109 



purposes of motion and locomotion. Many of these 

 forms are further provided with fixed oral openings 

 surrounded by cilia directing currents into a tubular 

 aperture terminating abruptly in the cytoplasm, but 

 acting as a primitive alimentary canal. 



Likewise we find the desmids and diatoms among the 

 vegetable cells provided with complex cellulose enve- 

 lopes and silicious skeletons, and foraminifera and radi- 



c 



FIG. 34. Carchesium. Showing beginning specialization. (Greenwood.) 

 The path which the food takes is represented by dots, a (circular round 

 marks) represents the position of storage; 6 (crosses) represents the position of 

 rest; c (dots), the region of the later changes. 



olaria among animals with wonderfully elaborate sili- 

 cious skeletons which endow the organism with definite 

 form and increase its rigidity. 



These primitive specializations find their homologues 

 in the dermal coverings, the limbs and fins, etc., of the 

 higher animals. 



It is self-evident, however, that an organism composed 

 of a single cell is less well able to increase its complexity 



