I-IFE-CYCLE OF " CYSTOBIA " lEEEGULAllIS (mINCH.). 11 



the gut, but^ after laborious examination of a great many 

 sections, no traces of Cystobia could be found. ^ 



(3) Habitat and Mode of Life. 



(ft) C. irregularis. 



Mincliin (loc. cit.) lias described the general habitat of this 

 parasite and its relation to the vascular system. This is well 

 shown in his figures 9, 10, and 19, and also in my figures 5, 20, 

 and 41. Some additional observations, however, may be noted. 



Trophozoites — as both young forms and adults are termed 

 while they are still taking in nourishment — occur chiefly in 

 the complex vascular meshwork, known as the "rete mirabile," 

 which is attached to the second loop of the gut, the intestine 

 proper. This is essentially the region of absorption, and the 

 fluid circulating in these finely anastomosing vessels is doubt- 

 less very rich in nutrient solutions. Hence it is particularly 

 suitable for the gi-owing Gregarines, which probably pass 

 into it directly from the intestine. 



Histology of the vascular network. — The structure 

 of this network differs considerably from that of the more 

 anterior part of the vascular system, which runs along the 

 first, or what may be called the stomach, loop. In the latter 

 the longitudinal vessels are much more distinct and of larger 

 calibre, and the vascular plexus is much simpler. The chief 

 difference, however, is in the wall. That of a main vessel or 

 connecting branch in this anterior region is very thin and 

 transparent-looking, and pale or slightly reddish in colour. 

 In section (fig. 7, pi. 1) it is seen to consist of loose, spongy 

 cells {s-p. c), bordering- and traversing the lumen irregularly, 



^ A reason for these unsuccessful infections is perhaps to be found in the 

 fact that, in the majority of spore-containing cysts, subsequent examination of 

 stained material showed that the spores themselves were not ripe, having only 

 four nuclei. This preponderance of the four-nuclear stage was noticed by 

 Minehin (loc. cit.). Probably the enclosing epithelium often breaks dowu 

 before the sporozoites are fully formed, and the spores ripen either in the 

 body. cavity or after expulsion from the host (see below, in text). 



- The vessels have no true epithelial lining internally. 



