58 PROTOZOA. 



that they separate and encyst separately. As a rule, however, they 

 remain together, and a cyst-wall is secreted round the syzygium ; but 

 even in this case the fusion of the conjugating individuals does 

 not appear always to be complete, for the line between them can 

 frequently be seen until the spore-formation has begun. In Diplo- 

 cystis and Gamocystis conjugation occurs very early, so that it is 

 rare to find any but very small forms not united with another in 

 conjugation. This precocious conjugation may take place some time 

 before encystment. The internal processes accompanying conjugation 

 have not been thoroughly made out, but it appears that the nuclei of 

 the conjugating pair meet in the bridge of protoplasm which connects 

 the two bodies, and there fuse to form a zygote-nucleus. This divides 

 and gives rise to a number of nuclei, which travel to the surface and 

 are budded off with a certain portion of the protoplasm as the small 

 rounded spores. The protoplasm of the syzygium is more or less 

 used up in this process, but there generally appears to be a certain 

 amount (residual protoplasm) left over, unchanged, in the cyst. The 

 uninucleated spores acquire a chitin-like coat, which has often a 

 spindle-shaped, oval, or oblong form, and in this condition are called 

 pseud 'ojiavicelhe.* The contents of the pseudonavicellae divides longi- 

 tudinally into a number, generally six to eight, of sickle -shaped 

 structures called the falciform bodies, and into a small amount of 

 residual protoplasm, which disappears. The falciform bodies on the 

 bursting of the cyst and the solution of the spore-case become young 

 Gregarines. It thus appears that the young Gregarines arise by the 

 division of the spore -protoplasm. "When first liberated from the 

 case, the young often perform active serpentining movements and 

 make their way into a cell of their host (generally a new host, 

 but in endogenous spomlation it may be the same host, see below), 

 in which they increase in size, until they grow too large for the 

 cell and project into the neighbouring space. Eventually they 

 become detached and lie freely in the organ they infest alimentary 

 canal, testis, kidney, or whatever it may be. Some of the forms 

 are only knoAvn in the full-grown free condition, and we cannot 

 therefore be certain that they are intracellular in habit in the 

 young stage. The spores escape by the bursting of the cyst, or in 

 some cases through sporoducts which are formed in the protoplasm 

 of the syzygium and everted through perforations in the cyst-wall. 



As a general rule conjugation precedes the formation of the cyst, 

 but encystment of solitary forms and subsequent sporulation has been 



* In Porospom yigantca of the lobster the spores are naked. 



