THE XEOSPORIDIA 403 



An example of the Disporea is Ceratomyxa drepanopsetta;, of which the 

 spore-formation is described by Awerinzew (759). The trophozoite has at 

 first only two nuclei, which are considered by Awerinzew to be derived, 

 ''beyond all doubt," from division of a single nucleus; it seems far more 

 probable, on the contrary, that the binucleate trophozoite is to be derived 

 from the association and fusion of two distinct planonts. In the binu- 

 cleate trophozoite each nucleus divides by karyo kinesis into two nuclei, 

 a larger and a smaller (Fig. 166, A). The two smaller nuclei are vegetative, 

 the two larger generative, in function. Round each of the two generative 

 nuclei the protoplasm becomes concentrated so as to form two cells which 

 lie embedded in the endoplasm of the trophozoite. These two cells are usually 

 of distinctly different sizes, and represent a microgametocyte and a macro- 

 gametocyte respective!}'. Each gametocyte next divides into two gametes 

 (Fig. 166, B, C, D), and in each gamete a certain amount of chromatin is 

 extruded from the nucleus, first into the cytoplasm of the gamete, and then 

 into the endoplasm of the mother-trophozoite. Then each microgamete 

 copulates with one of the two rnacrogametes (Fig. 166, E, F). The two 

 zygotes thus formed represent the sporoblasts, each of which forms a spore 

 independently of the other. 



Each sporoblast divides into two cells, a larger and a smaller (Fig. 166, G), 

 and the smaller divides again into two (Fig. 166, H) ; the result is an aggregate 

 of three cells : a larger, which gives rise ultimately to the two parietal cells 

 which form the valves of the sporocyst, and may be termed the " sporocyst- 

 mother-cell " ; and two smaller cells, one of which is the mother-cell of the 

 two capsulogenous cells, the other the future sporozoite or amcebula. The 

 sporocyst-mother-cell may become temporarily separate from the capsule- 

 mother-cell and the amcebula. 



The three cells of the previous stage build up the spore in the following 

 manner : The sporozoite grows in size, and its nucleus divides into two. The 

 capsule-mother-cell divides into two capsulogenous cells, each of which 

 forms a polar capsule in its interior. The amcebula and the two capsulogenous 

 cells are placed close together and arranged in a definite manner (Fig. 166, 7). 

 The sporocyst-mother-cell divides into two parietal cells (Fig. 166, J), which 

 place themselves on either side of the cell-complex composed of the associated 

 amcebula and capsulogenous cells (Fig. 166, K), and each secretes one valve 

 of the sporocyst enveloping the whole complex. 



Thus the trophozoite consists finally of an amoeboid body containing two 



FIG. 166. Spore-formation in Ceratomyxa drepanopsettce. A, Trophozoite sketched 

 in outline, showing in the plasmodium two generative nuclei (g.), each sur- 

 rounded by a cell-body, and two vegetative nuclei (v. ), which lie in the pro- 

 toplasm of the body (left blank) ; note that the generative cells are of different 

 sizes ; B, C, the two generative cells have divided each into two, so that 

 there are now two macrogametes ( $ ) and two microgametes ( $ ) ; chromatin 

 is being given off from the nuclei of the gametes into the cytoplasm ; D, each 

 microgamete is apposed to a macrogamete ; the chro matin-bodies given off 

 by the gamete-nuclei are now extruded into the plasmodial body ; E, F. 

 stages in the syngamy between the gametes ; in E the cell-bodies are fused, 

 in F the zygotes (z.) are complete ; G, each zygote (sporoblast) has divided 

 into a larger (p) and a smaller cell ; H, the smaller cell in each sporoblast 

 has divided into two, the capsule-mother-cell (c.m.) and the sporozoite (am) ; 

 the larger cell (p.) is the mother-cell of the parietal cells ; I, a single sporoblast 

 showing the parietal mother-cell (p.) still undivided, the sporozoite (am) 

 with its nucleus divided into two, and two capsulogenous cells (e.g.) derived 

 from division of c.m. in H ; J, a trophozoite showing the two parietal mother- 

 cells of H each divided into two parietal cells (p.') but still separate from the 

 cell-complex consisting of the binucleate sporozoite (am) and the two capsu- 

 logenous cells (e.g.) ; K, union of all the cell-elements of the spore ; the two 

 parietal cells (p.') surround the cell-complex (drawn on a smaller scale than 

 the last figure) ; L, spore nearly fully formed : n.p., nucleus of a parietal 

 cell ; am, sporozoite with two nuclei (n.g.) ; p.c., polar capsules. After 

 Awerinzew (759). 



