THE SPOROZOA 165 



bodies of the two associates into a number of minute nucleated 

 corpuscles or gametes, which conjugate in pairs. Thirdly, 

 there is the formation of resistant spores by whose means the 

 parasite is disseminated and introduced into new hosts. The 

 course of these events is as follows. Two mature trophozoites 

 which as they are destined to give rise to gametes may now 

 conveniently be called gametocytes, come together in close 

 apposition (fig. 34, E and F). While retaining their individu- 

 ality, they lose their characteristic form, become hemispherical, 

 and together form a subspherical mass, which undergoes slow 

 rotatory movements while secreting a cyst-wall from its surface. 

 First an outer rigid epicyst is formed, afterwards an inner thin 

 and soft endocyst. During the formation of the cyst the two 

 associated gametocytes shrink in size and a space filled with 

 fluid is formed between them and the cyst-wall, but although 

 enclosed in a common envelope, they are still perfectly distinct 

 from one another and separated by their cuticles at the surface 

 of contact. While the cyst is being formed the nucleus of 

 each gametocyte undergoes changes preparatory to division. 

 The karyosomes diminish in volume and are partly dissolved 

 in the nuclear sap, while in their place small granules or short 

 filaments of chromatin make their appearance. A centrosphere 

 with astral rays appears outside the nucleus ; the nuclear 

 membrane disappears and a mitotic spindle is formed which 

 elongates until it stretches right across the body of the 

 gametocyte (fig. 34, G). The two daughter-nuclei resulting 

 from the division are smaller than the parent nucleus and 

 situated at opposite ends of the body. They divide again 

 with mitosis to form four grand-daughter nuclei of smaller 

 size, and the process is separated again and again. At each 

 division the nuclei reform, rest awhile, and then undergo 

 a fresh mitotic division. Eventually a large number of minute 

 nuclei are formed, mostly collected near the periphery of each 

 gametocyte. Throughout this period the two associated 

 individuals have retained their identity, but now the cytoplasm 

 of each divides into several irregular fragments each containing 

 a number of nuclei projecting from its surface. The nuclei 

 then become surrounded by clear protoplasm, which is pre- 

 sently segmented into a number of small ovoid cells, each 

 containing a single nucleus and attached by its base to the 

 residuum (fig. 35, A*). The minute nucleated cells thus 



