LIFIS-OYCLE OF " CYSTOBIA " lEKEGULAlHS (mINCH.). 19 



(4) Form, Size, and General Appearance. 

 (ft) C irregularis. 



Observed living and " free/' the parasites never showed 

 the least tendency to displace themselves; neither did I notice 

 anything comparable to englenoid movements causing flexion 

 or constriction of the body/ such as Brasil (2) figures in the 

 case of Urospora lagidis. Changes in shape, e.g. the 

 rounding off of the Gregarines, on encysting are probably 

 more passive than active — that is to say, impressed, as it were, 

 upon them by their relation to the surrounding tissue ; and 

 the same applies equally to C. minchinii. In short, the 

 Gregarines appear tobe perfectly n:otionless;~ this peculiarity 

 will be readily understood when the minute structure of the 

 peripheral region of the body has been described. 



The typical form of an adult trophozoite, really of a double- 

 adult or "couple," is that of a beautifully symmetrical ovoid. 

 Fig. 1, pi. 1, represents a medium-sized parasite, its length 

 being "5 mm. and its greatest width "25 mm. Around the 

 middle of the body is a slight, V-shaped constriction, causing 

 a break in the contour of the side. This marks the plane of 

 junction of the two members of the couple, which is further 

 indicated by the distinct septum running transversely across 

 the body." The two halves are always, so far as can be seen, 

 of equal size. In each is a perfectly spherical nucleus with a 

 single large karyosome. Another rather larger trophozoite, 

 obtained free of the vessel and scarcely so perfect in outline, 

 is shown in fig. 2. Here the union is complete, there being- 

 no perceptible break in the contour, and the couple might be 



' Irregularities in contour, such as Mincliin (loo. cit.) mistook lor the 

 normal appearancej are undoubtedly the result of deformation. 



2 Brasil, iu a quite recent paper (3), characterises Gonospora varia as 

 " completely immobile." This coelomic parasite is, indeed, probably closely 

 related to C irregularis (see under Systematic Position, p. 60). 



3 The reasons why this septum is considered to represent a plane of union, 

 and not a separating partition or plane of division, will be discussed later (see 

 below, p. 65). 



