riFE-CyCLE OF "CYSTOBIa" IKrvEGULAEIS (mINCH.). 75 



As the life-cycle of any Gregaviue becomes completely 

 known, it will almost certainly be found that each individual 

 is, at some time or other prior to the commencement of 

 sporulation, associated with a fellow one, such association being 

 in nearly all cases permanent, and. followed by encystment 

 and true conjugation. I have not been able to find a single 

 instance Avhere it has been definitely proved that a single 

 Gregariue, which has never associated, can sporulate, 

 and the more life-histories that are thoroughly investigated 

 the more unlikely does such an occurrence become. Siedlecki, 

 Cuenot, Berndt, and Leger, in their recent researches, respec- 

 tively emphasise the fact that they never observed single 

 encystment at all. Brasil observed solitary encystment occa- 

 sionally in Gonospora and Urospora, but it was unsuc- 

 cessful; thenuclearmultiplicationwasabnormaland the cystfell 

 a prey to the phagocytes of the host. Still, one or two authors 

 have described the occurrence of normal solitary encystment, 

 and appear to consider that successful sporulation without 

 conjugation (i.e. parthenogenesis) results. These instances 

 are considered below. What I maintain, however, is that, 

 granting such cases do occur, in all probability there has 

 been a temporary association previously, when the develop- 

 mental stimulus was imparted ; and, indeed, where solitary 

 sporulation is described, temporary association is usually 

 mentioned as also taking place. 



Relation betAveen association and conjugation. — 

 We may now compare the varying relations between associa- 

 tion and conjugation which we find in the group. The least 

 modified condition is seen in the Septate Gregarine Ptero- 

 cephalus, where there is markedly anisogamous conjuga- 

 tion, after association and common encystment of the couple 

 (see Leger and Duboscq [23]). Now, it is obvious, when the 

 formation of gametes became delayed until after association, 

 and their successful copulation was thus practically insured, 

 there Avas no longer the same necessity for the gametes to 

 be differentiated. Hence, as might be expected, Ave find a 

 reduction to isogamy taking place, of Avhich Stylorhynchus 



