PIGMENT TISSUES 



273 



the pigmented secretion (Fig. 235, A and D). The glandular pouches 

 eventually burst, and the elaboration of pigment continues at the ex- 

 pense of the cytoplasm until there remains but the nuclei inclosed in 

 a shallow layer of cytoplasm (Fig. 235, A and ). These nuclei and 

 their cytoplasm finally disintegrate. 



In Vampyrella we have a beautiful example of pigmentation which 

 shows how closely diffused pigment may be associated with assimila- 

 tion. This simple animal is frequently found living with cultures of 

 fresh-water, green Algae. It consists of a film of colorless protoplasm 

 bearing numerous refractive granules. The sheet of protoplasm, when 

 containing no food bodies, is little more than a micron thick. When 





FIG. 236. A-C, three stages in the life-history of a Vampyrella. A, with freshly ingested green 

 food plants; B, food plants turned to a reddish brown; C, the animal departing from its 

 encysted state as three reddish brown individuals. X 725. 



food is ingested, the protoplasm forms a rounded mass about which 

 an encysting membrane is formed. The animal remains quiet while 

 the food is being digested. As digestion proceeds, the plants taken in 

 as food change from green to brownish red. The food decreases in 

 size as its digested parts are absorbed from the food vacuole. The 

 protoplasm becomes pigmented by the assimilated food, so that when 

 the protoplasm breaks from the cyst as a free animal or animals, .it is 

 conspicuously colored brownish red (Fig. 236, A, B, and C). 



Metopus furnishes an example of segregated pigment within a 

 cell. Metopus is a simple, ciliated infusorian found very frequently 

 in old infusions. It will be readily recognized from our Figure 237. 

 At the anterior end is a patch colored dark brown to black. This, 



