THE SPOROZOA 229 



It is thus seen that the life- cycles of the Coccidia can be 

 arranged in what is evidently a natural series ; but it is open to 

 debate which end of the series should be considered as the more 

 primitive, and should be taken as the starting-point of the evolution. 

 The tendency of modern authorities has been rather to consider the 

 condition in Coccidium as primitive, and to regard Benedenia as a 

 form in which the alternation of generations is secondarily sup- 

 pressed. It does not, however, seem probable that a method of 

 reproduction so useful to the parasite as the schizogony would have 

 been abandoned when once acquired, and the existence of the vast 

 legion of Gregarines, in which schizogony is of the rarest occurrence, 

 makes it probable that in Coccidia also the primitive ancestral 

 type was without schizogony, and that the alternation of genera- 

 tions has been acquired by the majority of the group as an 

 adaptation to parasitic life. But even assuming the correctness of 

 this view, it does not necessarily follow that the case of Benedenia 

 itself is primitive. More intimate acquaintance with the life-cycles 

 of different Coccidia is necessary before a definite opinion can be 

 framed with regard to this point. 



(c) Classification. The order Coccidiidea is divided into families 

 characterised by the number of sporocysts (if any) formed within 

 the oocyst. Generic characters are sought chiefly in the number of 

 sporozoites formed in each spore, and to a less extent in the form 

 and characters of the sporocyst. Four families are thus recognised, 

 but the differences which separate the first of them, the Asporo- 

 cystidae, from the -other three are such as should give it the rank of 

 a sub-order rather than a family. 1 



1 The classification of Labbe [4] is founded upon the number of uninucleate 

 masses or archispores into which the schizout or sporont divides up in the first 

 instance. In Eimeria each archispore becomes a sporozoite ; in other forms each 

 archispore becomes a sporoblast which secretes the sporocyst, and then may further 

 divide up to form sporozoites. On this basis of division Labbe founds two sub-orders 

 I. Polyplastina, with numerous archispores (Eimeria, Klossia, Adelea, etc.) ; II. 

 Oligoplastina, with few (2-4) archispores (Coccidium, Diplosp&ra, etc.). 



Lt'-ger [47] considers that the primary subdivision of the Coccidia should be 

 based upon the number of sporozoites formed in each oocyst. He therefore classifies 

 them as follows : 



A. Coccidia with polyzoic oocysts, including (1) Aspvrocystidae (Eimeria), with 

 no sporocysts ; and (2) I'olysporocystidae, with sporocysts, which are monozoic 

 (Barroitssia), dizoic (Adelea), trizoic (Benedenia), or tetrazoic (Klossia). 



B. Coccidia with octozoic oocysts, including (1) Disporocystidae, with two tetrazoic 

 sporocysts (I)iplospora) ; and (2) Tetrasporocystidae, with four dizoic sporocysts 

 ( Coccidium, C'rystallospora). 



C. Coccidia with tetrazoic oocysts, including one genus (and family ?) Cyclospora, 

 with two dizoic sporocysts. 



Mesnil [49], on the other hand, divides the Coccidia into two divisions, the 

 Asporocystea and the Sporocystea. The Asporocystea are to include the Asporo- 

 blastease Monosporoblastea, for the species Leyerel/a (Eimeria) nova, andtheSporo- 

 lilastea, for the malarial parasites. The Sporocystea are the ordinary Coccidia. 



It should be noted that the four families of Coccidia now generally recognised are 

 not named in accordance with the accepted rules of zoological nomenclature, which 

 require that a family should be named from its type-genus. Thus the Asporocystidae 



