PROTOZOA 



23 



cystment is characteristic for certain groups (Fig. 3). These 

 spores sometimes have an amoeboid movement ; sometimes 

 they have a rather long, delicate, threadlike appendage, a 

 protoplasmic process called a flagellum. This is capable of 

 rapid vibration and functions as an organ of locomotion ; such 

 spores are said to be flagellate. In some cases two individuals 

 may fuse with one another before encysting, but just how much 

 significance should be attached to this process — here called 

 conjugation — it is difficult to say. 



Encystment is not always followed by spore formation and 

 may have no connection with reproduction. Thus some of 

 the Rhizopoda secrete a cyst around themselves after they 



D 









\ 



-■ tw- 



J K - 

 E F G 



Fig. 3. Pseudosfora, parasitic in the celis of fresh-water algae. A, the adult 

 individual as it exists within the plant-cell; B, encysted; C, protoplasm divid- 

 ing into spores, with a residual body; D, flagellate spores escaping from cyst, 

 leaving residual body behind; E, flagellate spore as it makes its way into a 

 new plant-cell ; F, G, development of the spore into the amoeboid form of the 

 adult. (From Delage and Herouard's Traite de Zoologie.) 



have ingested a large amount of food, and when digestion is 

 completed they emerge from the cyst. Or encystment may 

 occur when the surroundings of the animal are unfavorable, as 

 when there is a scarcitv of food or of moisture ; thus the inch- 



J 



vidual remains protected until a more favorable season. 



The class Rhizopoda may be divided conveniently into three 

 orders, omitting the Mycetozoa, sometimes placed here, which 

 we have already considered. 



Order 1. Foraminifera 



The Foraminifera (Lat. foramina, holes, and /r/vr, to bear) are 

 mostly marine Rhizopoda, although there are not a few lresh- 

 water representatives. They creep along the bottoms of quiet 



