AMCEBA—GREGARINA. 



87 



have an excretory function, and serve to get rid of the finer 

 waste products. 



Life History. — In favourable nutritive conditions the 

 Amoeba grows. At the hmit of growth it reproduces by 

 dividing into two. In disadvantageous conditions, such as 

 drought, it may become globular, and secreting a cell wall or 

 cyst, lie dormant for a time. With the return of favourable 

 conditions it revives, and, bursting from the cyst with 

 renewed energy, begins anew the cell cycle. The conjuga- 

 tion of two Amcebffi has been observed, and it is said that 



Fk;. 16. — Life history of Amreba. 



1. 7t. Nucleus, c.v. contractile vacuole. 



2. Division into two 



3. Encyst.ition. 



4. Escape of amoeba from its cyst. 



spore formation occasionally occurs ; of these processes, 

 however, little is certainly known. 



Second Type — Greg.a.rina. 



Gregariiia, a type of those Gregarinida or Sporozoa in 

 which the cell is divided into two regions by a partition. 



Description. — Various species occur in the intestine of the 

 lobster, cockroach, and other Arthropods. When young they 

 are intracellular parasites, but later they become free in the 

 gut. They feed by absorbing diffusible food stuffs, such as 

 peptones and carbohydrates, from their hosts, and store up 

 glycogen within themselves. The maximum size is about 

 one-tenth of an inch. There is a firm cuticle of " proto- 

 elastin," which grows inwards so as to divide the cell into a 

 larger nucleated posterior region and a smaller anterior region, 

 and also, in the young stage, forms a small anterior cap. The 



