COCCIDIA 



573 



cytomeres first appear and then merozoites; alternation of genera- 

 tions and of hosts which are marine annelids, molluscs and crus- 

 taceans. 



Genus Aggregata Frenzel. Schizogony in a crustacean and sporo- 

 gony in a cephalopod; zygote produces many spores, each with 3 

 sporozoites. Many species. Cytology (Moroff, 1908). 



Fig. 245. Ovivora thalassemae (Mackinnon and Ray)- a, two mature 

 organisms in host egg, seen in reflected light, X250; b, schizonts in sec- 

 tioned egg; c, micro- and macro-gametocytes in an egg, X500; d, two 

 maturing microgametes still attached to cytoplasmic residuum, X1075; 

 e, cyst with zygotes in some of which nuclei are dividing, X500; f, a spore 

 with 10 nuclei, X900. 



A. eberthi (Lab-be) (Fig. 246). Schizogony in Portunus depura- 

 tor and sporogony in Sepia officinalis. Spores (a) germinate in the 

 crab gut, each liberating 3 sporozoites (b) which grow and produce 

 merozoites (10/x by 2/x) by schizogony in peri-intestinal connec- 

 tive tissue cells (6 chromosomes) (c-/); when host crab is eaten by 

 a cuttlefish, merozoites penetrate gut wall and develop into mi- 

 cro- and macro-gametocytes (h, k), and further into gametes (j-l); 

 anisogamy (m) produces zygotes; zygote nucleus contains 12 

 chromosomes which become divided into 2 groups of 6 in the first 

 division (n, o); repeated nuclear division (p) forms many sporo- 

 blasts (q), each transforms itself into a spherical spore with 3 sporo- 

 zoites (Dobell, 1925; Naville, 1925; Belaf, 1926). 



