32 ILLINOIS BIOLOGICAL MONOGRAPHS [242 



LIFE HISTORY OF A TYPICAL CEPHALINE GREGARINE 



The life history may be outlined briefly as follows: Sporozoite — tro- 

 phozoite — sporont — gamete — zygote — spore — sporozoite. The sporozoite 

 is a very minute falciform body liberated from the spore by the action of 

 the digestive juices of the host which has swallowed it.* This small body 

 apparently possesses no means of locomotion other than the extrusion of 

 protoplasm. It lodges among the cilia of the intestinal epithelium and 

 bores its way into the cell by ameboid movement. (Leger and Duboscq, 

 1909). Penetration is probably effected by the excretion of a toxin 

 which lowers the resistance of the cell wall. It either merely punctures 

 the wall and projects a small portion of its body into the cell, as in most 

 Gregarinidae, or completely embeds itself in the cell mass, deriving its 

 nourishment from the cell sap, as in the Stenophoridae. As soon as the 

 sporozoite begins to absorb nourishment and to grow, it becomes a tro- 

 phozoite. A combination of factors determines when the trophozoite 

 shall be liberated into the lumen of the cell. The destruction of epithe- 

 lial cells and the growth of the parasite go hand in hand and when the 

 cells no longer supply sufficient nourishment or when the activity of the 

 parasite causes it to release its hold, the trophozoite is liberated into the 

 intestine and thenceforth absorbs nourishment from the fluids of that 

 cavity. 



After the cell has been destroyed and the parasite liberated, the epi- 

 merite is no longer useful and drops off. With the loss of the epimerite 

 and change in habitat, the animal becomes a sporont. At some stage in 

 sporont life, generally an early one, a member of the genus Gregarina 

 attaches to one end of the body another sporont, the two forming an as- 

 sociation. In genera in which the sporonts are solitary, attachment of 

 two sporonts takes place just previous to cyst formation. Upon reach- 

 ing a certain size or density or because of some unknown internal factor, 

 the two sporonts rotate about a common axis and form a sphere. This 

 spherical mass acquires a relatively thick gelatinous covering, the cyst, 

 and leaves the body of the host with the feces. If it remains in a moist 

 place for 48 hours, development proceeds as follows: The sporont nu- 

 cleus breaks up into a myriad of small chromidial bodies, each small 

 body acquiring a small amount of the residual protoplasm of the sporont. 

 These nucleated particles are gametes. The gametes of the two sporonts 

 are allowed to mingle by the beaking down of the separtion walls, when 

 they fuse two by two and form zygotes. The zygote acquires a tough, 

 resistant transparent covering and the content breaks up into eight parts, 



♦There is some evidence to substantiate the theory that autoinfection occurs 

 and accounts for the enormous number of parasites which is often present in a 

 host. See last page of section on cysts. 



