GREGARINA. 



87 



cell into a larger nucleated posterior region and a smaller 

 anterior region, and also, in the young stage, forms a small 

 anterior cap. The cell-substance is divided into a firmer 

 cortical layer and a more fluid central substance. The 

 protoplasm often presents a delicate fibrillar appearance, 

 suggesting that of striated muscle. The nucleus is very 

 distinct, but there are no vacuoles. We may associate the 

 absence of locomotor processes, " mouth," and contractile 

 vacuoles, as well as the thickness of the cuticle and the 

 general passivity, with the parasitic habit of 

 the Gregarines. It is not clearly understood 

 how these and other intestinal parasites have 

 become habituated to resist the action of 

 digestive juices. 



Life history. — The young Gregarine is 

 parasitic in one of the lining cells of the gut ; 

 it grows, and, leaving the cell, remains for a 

 time still attached to it by the cap (Fig. 35, 

 a., yg.) ; later this is cast off, and the indi- 

 vidual becomes free in the gut, while still 

 increasing in size. Two or more individuals 

 attach themselves together end to end, but 

 the meaning of this is obscure. Encystation 

 occurs, involving a single unit or two to- 

 gether, and from the division of the encysted 

 cell or cells, spores are formed. All the 

 protoplasm is not always used up in forming 

 the spores, but a residue may remain, which 

 forms a network of threads supporting the 

 spores. The cyst is sometimes (as in G. 

 blattarum) complex, with "ducts" serving 

 for the exit of the spores, each of which is 

 surrounded by a firm case. Eventually the 

 cyst bursts, the spore-cases are liberated, and from within 

 each of these the single spore emerges to become a cellular 

 parasite. The spore of G. gigantea is at first non- 

 nucleated ; it gives off two processes, one of which becomes 

 detached, vibratile, and nucleated, while the other seems 

 to come to nothing (Fig. 35, sj> 2 ). The adult of this 

 species is sometimes three-quarters of an inch in length — 

 enormous for a Protozoon. 



Fig. 34.— End- 

 to-end union 

 of Gregarines. 

 — After Fren- 

 zel. 



