74 H. M. WOODCOCK. 



occuivence of sucli association;^ in otlier words, the process 

 acquired a distinct physiological import, in that by it a 

 developruental stimulus was imparted to each associate. We 

 thus arrive at the present-day condition in the group. 



Essential importance of the process. — Association 

 is necessary in the great majority, if not in all, Gregarines for 

 sporulation to take place; in other words, we may say that an 

 interacting stimulus such as is mutually exerted by the two 

 associates is requisite to produce the formation of gametes or 

 primary sporoblasts, and without it the animals are unable to 

 fulfil their complete life-cycle.- A very interesting parallel 

 case, proving that association may undoubtedly become neces- 

 sary for the production of gametes, is seen in the Coccidia. 

 Here, with the exceptions to be mentioned, the phenomenon 

 is unknown, the gametocytes giving rise to the gametes 

 apart and quite independently. In Adelea mesnili, how- 

 ever, we generally find association of the male and female 

 gametocytes either in the same or in neighbouring cells. 

 The male individual (microgametocyte) may, however, still 

 develop microgametes apart from the female individual 

 (megagametocyte), but in that case they come to 

 nothing (seePerez [30]). In Adelea ovata and Klossia 

 helicina, on the other hand, unless the male gametocytes 

 become associated with the female ones, neither can they 

 form male elements nor can the female cells matu- 

 rate and become ready for fertilisation (see Siedlecki 

 [38]). That is to say, we have here an attempt on the part 

 of certain Coccidia to imitate the highly successful expedient 

 of the Gregarines; and just as in the above mentioned para- 

 sites association is obviously necessary to induce the for- 

 mation of gametes (equivalent to sporoblasts), so it has 

 undoubtedly become in the vast majority of Gregarines. 



1 There are many examples of ripe solitary sporonts dying olT instead of 

 producing sporoblasts, and tliis is, in all likelihood, because they have been 

 unable to associate. 



' Siedlecki (loc. cit.) has already expressed a similar opinion with regard to 

 the stimulating effect of association, in the case of Lankesteria ascidise. 



