SKX I\ IM<()I()ZOA 193 



by the simple process of cndoiiiirosis, or rhc failure of a zygote to 

 undergo meiosis, perhaps the difference between these two types of 

 cycle is not of outstanding- importance in the evolution of these 



Order Coccidia 



In typical Coccidia there is pronounced anisogamy, but in the 

 Suborder I'.imeridea the macro- and microgametes are generally 

 formed independently of each other, the small flagellated microgam- 

 etes swimming to and fertilizing the large non-motile macrogametes. 

 In the Suborder Adeleidea the gamonts become associated before the 

 gametes arc produced. Although some of the older accounts of game- 

 togcnesis in the Coccidia indicated pregametic meiosis, nearly all 

 recent accounts show postzygotic meiosis, so that the vegetative 

 stages are haplonts (Table IV). 



Figure U shows diagrammatically the life cycle of Adel'ma 

 derovis, a typical member of the Adeleidea, as described by Hauschka 

 (1943). The zygote (1) nucleus undergoes a meiotic division (2, 3), 

 reducing the chromosome number from twenty to ten. A second 

 di\'ision produces four nuclei, two of which proceed to the next 

 division in advance of the other two (4). Other nuclear divisions 

 result in eight to fourteen, usually twelve, nuclei. The cytoplasm then 

 divides into uninucleated sporoblasts which surround themselves 

 with sporocysts to produce spores, each with two sporozoites (5, 6). 



Fig. T. 



1-48, stages in gametogenesis and sporogenesis of Urospora lagidis from Naville 

 (1927a). 1-8, stages in mitosis of female and 9-16 of male gamonts, second period of 

 development (note four chromosomes dividing and passing to each pole); in 3, 

 the eight chromosomes are explained as resulting from a precocious prophasic 

 separation of chromatids; 17-24, female, 25-32, male, stages in mitosis of third period 

 of development (two chromosomes pass to each pole); 33-48, development of 

 zygote and sporozoites; 33, fusion of gamete nuclei in zygote; 34, resting stage of 

 zygote nucleus; 35-40, first mitosis of zygote; 41, binucleate stage; 42-44, second 

 mitosis in zygote; 45, tetranucleate condition; 46, 47, eight nuclei following third 

 mitosis; 48, small abortive zygote. 49, "head" to "head" pairing of Stylorhynchus 

 oblofigatus, from Leger ( 1904). 50, anterior end pairing of Kalpidorhyncbiis arenicolae, 

 from Cunningham (1907). 51, lateral pairing, both "heads" together, in Cystobia 

 chiridotae, from Dogiel (1906). 52, lateral pairing, "heads" toward "tails" of Lecy- 

 thiufn thalassemae, from Mackinnon and Ray (1931). 53, macrogamete, 54, micro- 

 gamete, of Pterocepbahts nobilis, from Leger and Duboscq (1903). (All illustrations 

 redrawn.) 



