II 



PHYLUM PROTOZOA 



85 



and allied genera by the division of the body into two parts, 

 protomerite in front and deutomerite behind, by a sort of transverse 

 septum formed by an ingrowth of the layer of myonemes the 

 nucleus being usually situated in the deutomerite. Sometimes the 

 protomerite is produced in front into a process ending in a rounded 

 enlargement, the epimerite, which may be provided with radiating 

 spine-like projections (Fig. 64). When it escapes from the spore 

 the sporozoite in nearly all cases (Fig. 64, 7) enters one of the cells 

 of the epithelium of the alimentary canal of some member of the 

 higher animal phyla, and lives and grows there for a time as an 

 intracellular parasite (8). As it grows it comes to project into the 



3 



-n 



FIG. 64. Gregarina. Development from the sporozoite. 1, cells of the digestive epithelium 

 of the host ; 2, nuclei of the same ; 3, spore ; 4, spore discharging sporozoites (5) leaving 

 residual mass (6) ; 7, sporozoites in the act of entering epithelial cells ; 8, the same as 

 intracellular parasites ; 9-12, different stages in the growth of the young Gregarines into the 

 lumen of the intestine ; 13, epimerite ; 14, protomerite ; 15, deutomerite. (After Lang.) 



cavity of the canal (9, 10, 11, 12), and may eventually become entirely 

 free therein or in the body-cavity, or remain attached to the cell by 

 the epimerite. The formation of spores in Gregarina and its allies, 

 as in Monocystis, is preceded by the close apposition to one another 

 of two trophozoites and their enclosure in a common cyst. Such 

 conjugating trophozoites in Gregarina, as also in Monocystis, are 

 not of the nature of gametes : they are cells in which gametes are 

 produced and are appropriately named gametocytes. The cells 

 that result from the division of the nuclei and protoplasm of the 

 two associated gametocytes are the true gametes : they copulate. 

 i.e. completely coalesce, in pairs, each pair developing into a spore. 

 The two gametes the copulation of which leads to the formation of 

 a spore may be entirely alike ; but in some at least of the Gregarinida 



