OBSERVATIONS ON THE GREGARINES OF HOLOTHURIANS. 295 



nothing of the sort either in Gregarina irregularis or 

 Holothuria, and am inclined to think that what Mingazzini 

 took for spines were little bits of dirt (bacteria?) sticking to 

 the cyst, as commonly occurs. Nor have I observed anything 

 like the sporoduct described by Mingazzini, though it is quite 

 possible that a structure of this kind is formed later. The 

 internal cavity of the cyst is limited by a strong and distinct 

 membrane. 



All the cysts which I observed contained either spores or 

 sporoblasts. It was noteworthy that in the latter case the 

 cysts could be recognised by their contents being more or less 

 shrunk by the action of the alcohol, while in cysts containing 

 spores the inner mass was perfectly spherical. 



In the case of the sporoblasts, what I have described above 

 for G. irregularis is perfectly applicable here; they are 

 spherical bodies with a distinct membrane filled with strongly 

 refringent granules, and containing an internal nucleus appear- 

 ing as a clear space, as Mingazzini has already described 

 (p. 316). 



Fig. 24 represents a spore in outline x 730, and fig. 25, a and 

 hy two others with the contents drawn in, from a preparation 

 of Professor Biitschli. It can be seen that the spores agree 

 closely in the majority of details with those of G. irregularis. 

 Like them they are egg-shaped, and have a funnel-like ex-- 

 pansion of the cuticle at the narrow end. The cuticle has a 

 delicate external layer and a thick internal one, which stains 

 more readily, as Professor Biitschli first pointed out to me. 

 Both layers take part in the formation of the funnel, at the 

 base of which a thin diaphragm is formed by the internal layer. 

 But at first sight these spores appear to differ strongly from 

 those of G. irregularis in the fact that the external layer of 

 the cuticle is prolonged into a delicate caudal process — as we 

 may call it — at the broad end, which is nearly as long as the spore 

 itself. The caudal process is simply a flattened sheet-like ex- 

 tension of the cuticle ending in a point. At its edges it ap- 

 pears to be continuous with two ridges, which run forwards 

 along one surface of the spore to the funnel, curving inwards 



