i88 



THE SPOROZOA 



about double the length of the body, posteriorly, and as bearing 

 an undulating membrane which runs in a loose spiral from the 

 rostrum to the base of the flagellum. The microgametes fertilise 

 the " ova " in the usual way. 



Another and interesting variation in the type of conjugation 

 has been described by L6ger [21] in the genus Ophryocystis of the 

 Schizogregarinae. Here perfect isogamy obtains, combined with 

 reduction of the gametes. The sporonts become encysted to- 

 gether, separated at first by a septum (Fig. 31, c-/). In each the 

 nucleus divides into two, and one daughter nucleus degenerates 

 (Fig. 31, g). The remaining nucleus divides again, and again one 

 daughter nucleus degenerates (Fig. 31, h}. The survivor is the 

 pronucleus and represents one -fourth of the nucleus of the 

 sporont. The protoplasm of the sporont condenses round it to 

 form a single gamete, leaving a large quantity of residual proto- 

 plasm containing the degenerating nuclei. The two gametes 

 derived in this way, each from one of the original sporonts, fuse, 

 the septum becoming absorbed. Thus in each cyst is formed a 

 single zygote (Fig. 31, i, j), which develops into the single 

 spore, containing when ripe the usual eight sporozoites. Some- 

 times, however, the septum is not absorbed, and each gamete 

 then develops parthenogenetically, so that the cyst contains two 

 small spores instead of a single large one. It is evident that this 

 condition is to be derived from that in Monocystis by reduction and 

 degeneration of all the gametes formed from each gametocyte except 

 one. In the allied genus Schisocystis numerous gametes are formed 

 from each sporont, and conjugate after the manner of Monocystis. 

 The spores of Gregarines are either naked gymnospores 



or chlamydospores, invested 

 by a tough envelope. The 

 former condition is uncommon, 

 but is found in two genera of 

 Cephalina. In the first of 

 these, the genus Aggregate, 

 Frenzel, the gymnospores or 

 sporozoites are scattered in 

 the cyst round several residual 

 masses of protoplasm, giving 

 a certain resemblance to the 

 cysts of the malarial parasites 

 formed in the stomach of the 



tteres passing through a eoelomic cyst of Aggregaia niOSQuitO (Fig. 32). In the 

 coelomica, Leger. The numerous sporozoites (s) 11 



are arranged radially round masses of residual SCCOnd, the genUS Jrorospord, A. 



protoplasm (r.p). cy, cyst-wall; ep, intestinal o_i. n crkArr >lYlaefo oro Wmorl 



epithelium. (After Leger, x 180.) fecnn., sporoblasts are lormed, 



each of which gives rise to very 

 numerous sporozoites grouped round a central mass of protoplasm, 



FIG. 32. 

 Portion of a section of the intestine of Pinno- 



