170 



THE SPOROZOA 



portion of the body ; the intracellular stage or " Coccidian 

 phase" being practically suppressed. In other cases, again, a 

 large portion of the body, containing the nucleus, 

 is imbedded in the epithelial cell, while the rest 

 of the body projects freely from the host -cell. 

 But in typical cases the youngest trophozoites 

 are found as intracellular parasites, completely 

 enclosed by a cell of the epithelium, either of the 

 gut or some of its diverticula. In this situation 

 the parasite grows rapidly, and soon becomes 

 larger than the host-cell. The trophozoite then 

 falls out of the exhausted cell, usually passing 

 inwards towards the lumen of the gut, sometimes, 

 however, outwards into the vascular system or 

 body-cavity. Gregarines in the latter situation 

 are commonly termed "coelomic," without distin- 

 guishing whether the body-cavity in which they 

 lie is a true coelomic space or a part of the 

 haemocoele. Coelomic Gregarines, in the latter 

 sense, occur very frequently in insects (Fig. 9), 

 and in many cases a Gregarine may occupy 

 different situations at different periods of the 

 life of its host. It commonly happens that a 

 Gregarine inhabiting the digestive tract of an 

 insect -larva passes through the wall of the gut 

 at the metamorphosis, and so becomes a coelomic 

 Gregarine in the imago. 



The young trophozoites have been shown to 

 have remarkable effects upon the cells in which 

 they are parasitic. The infected host-cell passes 

 through two successive phases first one of 

 hypertrophy, then of atrophy. The facts have 

 been investigated by Laveran and Mesnil [16], 

 and still more recently by Siedlecki [28], in 

 The youngest trophozoites of Lankesteria ascidiae, 

 studied by Siedlecki, place themselves deep in the basal portion 

 of the epithelial cell, the region where the protoplasm of the cell 

 is least differentiated for secretion (Fig. 10, a). The nucleus 

 of the host-cell soon begins to appear swollen, its chromatin 

 network becomes loose and stains in a diffuse manner, and its 

 nucleolus increases greatly beyond the normal size, acquiring 

 irregular contours and often dividing into several parts. Hyper- 

 trophy of the nucleus is soon followed by that of the cytoplasm, 

 which appears clearer than in the adjacent cells, apparently as the 

 result of a sort of liquefaction. The protoplasm becomes difficult to 

 fix, and always stains much more feebly than the protoplasm of 



Larva of Tipida ole- 

 racea, opened to show 

 the gut covered with 

 coelomieGregarine 

 cysts. (From Wasie- 

 lewski, after Leger.) 



several species. 



