MONOCYSTIS. 



15 



of the worm are aggregated, and in consequence 

 the parasite may often be found covered with hair- 

 like structures, which in some species are the 

 adhering spermatids, but are hair-like outgrowths 

 of the pellicle in others. The trophozoite consists 

 of granular protoplasm enclosed in a pellicle, and is 

 capable of slight amoeboid movement. A mouth 

 is absent, nutrition being effected by osmosis of 

 the fluid contained in the vesicula seminalis through 

 any part of the cuticle. 



. Reproduction. 



When the trophozoite is full grown it becomes a gameto- 

 cyte and passes through a series of changes that 

 convert its protoplasm into spores. The changes 

 may be defined as (1) enclosure of two gametocytes 

 within a cyst ; (2) formation and fusion of gametes 

 or reproductive cells produced by the division of 

 each gametocyte ; (3) the formation of spore-coats 

 round the fused gametes. 



Two gametocytes come together and form a 

 common enclosing membrane. The nucleus of 

 each cell divides and subdivides into a great number 

 of small nuclei, which then travel to the surface of 

 each gametocyte, where they become surrounded 

 by a portion of the originally continuous proto- 

 plasm and form the gametes or germ-cells. So far 

 the events in each gametocyte have gone on inde- 

 pendently of those in the other. 



Now, however, conjugation of the gametes of 

 one gametocyte with those of the other takes place. 

 To allow of this, the partition between the two 

 gametocytes breaks down and allows free passage 

 of gametes in each direction, though how the move- 

 ment of the gametes is performed we do not know. 

 The nuclei and protoplasm of gametes having fused 

 in pairs, usually of different origin and of slightly 

 different character, a coat is formed about the fused 



