136 



BIOLOGY OF THE PROTOZOA 



many demands made upon it as a result of contact with the environ- 

 ment. These may be grouped as cortical differentiations for (a) 

 support and protection; (b) locomotion and irritability; and (c) food- 

 getting and defecation. 



A b c 



Fig. 73. — A, B, C, Form, structure of plates, and division of Coleps hirtus. 



Maupas.) 



(After 



(a) Cortical Differentiations for Support and Protection.— Apart 



from the thickening and hardening of the periplast which furnishes 

 sufficient protection and support for the great majority of flagellates 

 and ciliates, the cortex is the seat of precipitation of different 

 mineral substances; of secretion of gelatinous substances; or of 

 protoplasmic modifications into lifeless organic substances of various 

 kinds. These various products of cortical activity are moulded 

 into close-fitting, lifeless membranes of chitin, pseudochitin, and 

 cellulose, or into loosely-fitting shells, tests, skeletons, cups, tubes 

 and the like. These are not divided when the cell divides but are 

 either left as empty shells and tests, or one of the daughter indi- 

 viduals after reproduction remains in the old shell while the other 

 individual makes a new shell for itself. 



Gelatinous mantles are common in flagellates and are occasionally 

 found in the ciliates (/>. g., Ophrydium versatile), but gelatinous 

 materials are secreted by all types of Protozoa. Usually, when the 

 secretion is abundant, daughter cells remain embedded in it as a 

 matrix after division, and the so-called spheroidal types of colony 

 result (see p. 38). The ability to secrete gelatinous mantles as a 

 reaction to unusual stimuli appears to be very widely distributed, 

 if not universal amongst Protozoa. Bresslau (1921), using a variety 



