GREGARINIM; 



79 



After the fusion of the gametes, the copula assumes a spindle 

 form and secretes an envelope, and in this stage it is known as the 

 pseudo-navicella. Within the pseudo-navicella eight sporozoites are 

 formed, the result of repeated nuclear division, accompanied by division 

 of the cell (sporogony). These lie in the long diameter of the pseudo- 

 navicella and are arranged in such a way that their nuclei are all 

 congregated in the bulging central portion of the spindle. At a first 

 glance, the sporozoites appear also to be long and spindle-shaped and 

 to have the nucleus in the centre of the body. But it will be found 



O 



FIG. 22. Monocystis from the seminal vesicles of the earthworm, a, Cysts, during 

 the formation of gametes (gamogony). 6, Microgamete. c, Macrogamete. d t Copula, 

 before the fusion of the nuclei, e, Copula, during fusion of the nuclei. (After Brazil.) 

 Magnified, a, 600 : 1 ; b-d, 1,200 : 1. 



upon closer investigation that the nucleus is always placed at one pole 

 of the sporozoite, and that all the blunt nucleated poles occupy the 

 centre of the pseudo-navicella, while the pointed anterior poles run off 

 into its two ends. 



The pseudo-navicellae vary in size in earthworm Gregarines of 

 different species, their length varying from 0'015 mm. to 0'028 mm. 



(b) Gregarines of the Mealworm. 



Of the polycystic Gregarines, those most readily obtainable are the 

 varieties parasitic in the larvae of Tenebrio molitor, the mealworm, 

 largely cultivated as food for birds. Four such varieties are recog- 

 nized and, in spite of their similarity and the fact that they are found 



