BLOOD-PARASITES OF FISHES OCCUEEING AT ROVIGNO. 127 



parasites of both types occur^ and these are fairly plentiful. 

 We think the most probable explanation is that we have to 

 deal here with more than one infection. The great majority 

 of the small forms must be regarded as tlie early stages of a 

 new or recent infection ; the forms showing sexual differen- 

 tiation, on the other hand, belong, we think, to an older 

 infection. Most of them occur as adult large forms, and only 

 a few are to be met with as young or intermediate-sized indi- 

 viduals. The young parasites of the female type (belonging 

 to the older infection) are probably not very different in 

 appearance from the numerous small forms of ordinary type 

 (of the recent infection), and thus are only distinguishable 

 where they are beginning to grow into the stout type (fig, 14). 

 The two forms of merozoites, which give rise in time to the 

 large individuals, have doubtless been developed by a schizo- 

 gonous process,^ probably occurring in the internal oigans. 



The large forms themselves must represent one of two 

 phases, schizonts or gametocytes respectively. If, according 

 to the first of these interpretations, we have here micro- and 

 macro-schizonts which will give rise again to a fresh series of 

 micro- and macro-merozoites, it is evident that sexual dimor- 

 phism is apparent throughout the schizogonous series of 

 generations (as is known to occur among certain Coccidia, 

 e.g.Adelea, Cyclospora), If, on the other hand, our 

 two types are micro- and macro-gametocytes respectively, we 

 have no indications with regard to the nature of the ordinary 

 schizogony (or fission) in this parasite, which may be very 

 likely all ot one kind, that is to say, " indifferent " in 

 character, with no sexual dimorphism manifest (as in many 

 Coccidia and all known Heemosporidia). In this case it will 

 only be in the last generation produced by schizogony that 

 sexual dimorphism appears, in the formation of Avhat are 

 really the young micro- and macro-gametocytes (cf. above). 



Unfortunately, from our own preparations alone, Ave cannot 



' The process is, perha^js, comparable to the formation of merozoites 

 of two sizes in cysts of Karyolysiis (cf. Labbe [5]). both as regards 

 the development and the significance of the small elements formed. 



