LIFE-CYCLE OF " OYSTOTIIA " IRKEGULAKIS (iMINCH.). 13 



they most likely escape tlience when some Cuvierian organs 

 are extruded. Probably the stalk of attachment is here 

 stronger, in order to prevent the Gregarines breaking loose 

 and being carried away before spore-formation has proceeded 

 far; in H. tubulosa, which does not possess Cuvierian 

 organs, such a precaution is not necessary. 



There is no hard and fast line to be drawn with regard to 

 the condition the parasites are in when they evaginate the wall 

 of the blood-vessel. They may, as sporonts, have already 

 commenced nuclear division, or they may be quite young 

 trophozoites. In fact, the smallest example I obtained was 

 in the latter condition. Such cases are frequent towards 

 autumn^ when the lowering of the temperature and other 

 factors proclaiming the end of the season may perhaps induce 

 precocious evagination, in the endeavour to sporulate before 

 the appi'oach of winter. About one third of the adults met 

 with were "out," and had become rounded oif; the remainder 

 were, of course, in the lumen, and these possessed a perfectly 

 definite body-form. 



(h) C. minchinii. 



The habitat of C. minchinii in Cucumaria is very 

 different from that of C. irregularis. In the first place, 

 I never once came across the parasites in the vascular net- 

 work attached to the gut, strong a priori evidence that 

 they do not penetrate through the wall of this latter. The 

 most general situation is inside the respiratory trees, in the 

 wall of the branching and blindly ending diverticula. Here 

 they occur as white, opaque little spheres. PI. I, fig. 4, gives 

 an idea of part of a small diverticulum, which contained seven 

 Gregarines. When present, the parasites are sometimes very 

 numerous and all in a practically similar stage, only varying 

 in size. They range from 17ju to '20 mm. in diameter, and 

 between these limits all gradations in size are to be met with. 

 The smallest individuals I obtained were in this situation. 

 Figs. 31 and 32 show two of these tiny ones in section^ both being 



