98 PHYLUM PROTOZOA- -THE SIMPLEST ANIMALS. 



m 

 if 



or more individuals attach themselves together end to end, 

 but the meaning of this is obscure. Encystation occurs, 

 involving a single unit or two together, 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. 43, sp-). 

 The adult of this species is sometimes three- 

 quarters of an inch in length - - enormous 

 for a Protozoon. 



Sixth Type of Protozoa MONOCYSTIS. 



MonocystiS) a type of those Sporozoa in 

 which the cell is not divided into two parts 

 by a partition. 



Description. Two species (M. agilis and 

 M. magnd) infest the male reproductive 

 FIG. 42. End- organs of the earthworm almost constantly, 

 to-end union The full-grown adults are visible to the 

 Mt? a pren' na ^ed eye. They are usually flattened worm- 

 ze f. like cells, but the shape alters considerably 



during the sluggish movements. There is a 

 definite contractile rind, which is sometimes fibrillated, 

 and a more fluid medullary substance, in which the large 

 nucleus floats. In one species there is an anterior pro- 

 jection which resembles the cap of Gregarina, otherwise 

 unrepresented in Monocystis. As in Gregarina^ and many 

 other parasitic forms, a contractile vacuole is absent. 



Life history. The young form is parasitic within one of 

 the reproductive cells of the earthworm. It grows, and 





i 

 t 



