LIFE-CYCLE OP " CYSTOBL\ " IRREGULAELS (mINCH.). 87 



follows the usual plan. To Mincliin's description of the spore 

 it may be added that there is a deeply-staining plug or cap 

 closing the mouth of the inner spore membrane at the funnel 

 end; this is doubtless dissolved by the digestive juices of the 

 fresh host, thus allowing the sporozoites to pass out. 



The spore of D. rainchinii is very similar in form to that 

 of D. irregularis, but only about half the size. Tlie sporo- 

 cyst is veiy delicate, and is probably itself dissolved ; the fact 

 that I have not observed any ping at the base of the fiumel 

 also points to this conclusion. 



These two parasites are much more nearly related to each 

 other than is either to Cystobia liolothnrias, and for this 

 reason have been placed in a distinct genus. Diplodina 

 is undoubtedly closely allied to Gonospora; the affinities of 

 Cystobia holothuriee, on the other hand, are rather with 

 Lithocytis and Urospora. 



(10) The consideration of these neogamous Clregarines has 

 afforded a useful opportunity of discussing the phenomenon 

 of association as a whole. 



Considering first the variations in time and manner of the 

 process, we see that precocious and intimate association has 

 been especially developed in the three genera Diplocystis, 

 Diplodina, and Cystobia. These have proceeded along 

 rather different and independent lines, which reach their cul- 

 minating points in D. schneideri and Diplodina min- 

 chiuii respectively. In the former genus the desired result 

 is attained by successive (phylogenetic) modifications of the 

 encystment process ; in the latter (and also in Cystobia) the 

 tendency is towards intrinsic cytoplasmic union between the 

 two associates. 



Precocity of association is undoubtedly correlated with the 

 absence of movement in these ccelomic forms. It is simply 

 an endeavour to insure a suitable and durable association. 

 There is certainly nothing approaching true sexual conjuga- 

 tion, as yet, between the two members. Even where neogamy 

 is most intimate the nuclei remain, manifestly, quite distinct, 

 and I think the cytoplasm of each associate also retains its 



