330 THE PROTOZOA 



portion of the body develops into an epimerite which may acquire 

 a large size and a complicated structure. Originally attached to 

 one cell, which it destroys, the epimerite may acquire a secondary 

 attachment to other cells of the epithelium, which in this case are 

 not injured by it, as in Pterocephalus. Ultimately the epimerite 

 breaks off, and the body of the sporont drops into the cavity of 

 the digestive tract. In some cases (Pyxinid) the early attached 

 stages may free themselves from the epithelium several times, 

 and attach themselves again. 



3. When liberated from the host-cell, the trophozoite grows 

 into the adult sporont, which, as its future history shows, is a gamont 

 or gametocyte. A remarkable feature of gregarines at this stage 

 is the tendency to associate together (Fig. 7), a habit from which 

 the name Gregarina is itself derived. In some cases quite a number 

 of individuals may adhere to one another in strings ; such associa- 

 tions, known as " syzygies," are, however, of a temporary nature, 

 passing flirtations, as it were, which have no significance for the 

 life-cycle or development. On the other hand, a true association 

 of individuals destined to form gametes always, apparently, occurs 

 at one time or another in the life of the sporont. In the majority 

 of cases, however, the sexual association does not take place till 

 the end of the trophic phase, when the sporont is full-grown and 

 ripe for reproduction. But in a number of instances the associa- 

 tion takes place early in the trophic phase, between quite young 

 free trophozoites ; and " neogamous " association of this kind may 

 lead to almost complete fusion of the bodies of the two individuals, 

 only their nuclei remaining separate, thus producing the appear- 

 ance of a binucleate trophozoite (Fig. 70, p. 128). 



In general, the two trophozoites which associate are perfectly 

 similar in appearance, and exhibit no differentiation ; this is so 

 in all cases where they pair side by side. In some cases where 

 there is an early association end to end that is to say, where one 

 sporont attaches itself by its protomerite to the deutomerite of 

 another (Fig. 7, p. 9), as is common in polycystid forms the two 

 sporonts may be differentiated one from the other. In Didy- 

 mophyes, for instance, the protomerite of the posterior individual 

 disappears ; in Ganymedes the two sporonts are held together by 

 a ball-and-socket joint (Huxley). It is not known whether these 

 differences stand in any constant relation to the sex of the sporonts. 

 In Stylorhynchus the two partners attach themselves to one another 

 by their anterior extremities (Leger, 614). 



4. As soon as growth is completed, the reproductive phases are 

 in iated by the formation of a common cyst round the two asso- 

 ciated sporonts, which together form a spherical ma.ss (Fig. 144, a). 

 The parasite is now quite independent of its host ; it is, in fact, a 



