LIFE-CYCLE OF " CYSTOBIA " IRREGULARIS (mINCH.). 21 



parasite which I have seen are drawn in figs. 31 and 32. 

 The latter individual is only 18 n by 12 ^^ and from its 

 elongated form (not yet having become rounded off) looks as 

 though it had but recently passed from the lumen into the 

 wall of the respiratory tree. Its general appearance is 

 similar to that of the C. irregularis of fig. 30. The Gre- 

 garine in fig. 31 shows only one nucleus, but the other is 

 only one or two sections distant. Other, larger, trophozoites 

 in the same situation are seen in figs. 18 and 19, and in 

 neither is there any trace of a septum. The parasite in the 

 latter figure has a diameter of 0'15 mm. and the two nuclei 

 are far apart from each other, but in the other trophozoite, 

 which is rather smaller, they are again in contact. This 

 nucleai- contiguity ^ is purely accidental, and does not indi- 

 cate either nuclear union or separation ; in all cases the 

 nuclear membrane is quite intact. As in C. irregularis, 

 each nucleus has a single large karyosome. The body of 

 the parasite, when in this situation, is always practically 

 spherical, this being, probably, because it thus offers more 

 or less uniform resistance at all points to the surrounding 

 tissue-layers of the host. 



The true '^gregariniform" shape, however, is here also that of 

 a regular ovoid. This is exhibited by all the individuals which 

 are endeavouring to penetrate the coelomic epithelium. Two 

 of these are seen in figs. 9 and 10, the larger one being 

 Oo-l mm. in length by 0'2 mm. in width. Besides the invari- 

 able absence of any septum, another very constant feature of 

 this species, and one which distinguishes it from C. irregu- 

 laris, is the position of the nuclei. In a typical gregariui- 

 form adult the nuclei are always placed transversely (instead 

 of longitudinally) with respect to the long axis of the body, 

 and generally about one third of the animal's length from the 

 anterior end, designating thus the end which is farthest in. 



The transverse position of the nuclei in the gregariniform 

 adults of C. minchinii strongly suggests that the association 



* The same thing also occurs not infrequently in C. holothuriae, from 

 H. tubulosa (see Mincliin, loc. cit., fig. 21). 



