THE SPOROZOA 159 



on within the bodies of the gametocytes. In the nucleus of each 

 individual the karyosomes break up and become partially dis- 

 solved in the nuclear sap (Fig. 5, a-d, ky). At the same time a 

 number of chromosomes, in the form of grains or short filaments 

 of chromatin, appear grouped in a clump in the nuclear sap, 1 

 constituting a renovated chromatic nucleus which may be termed 

 the segmentation-nucleus (Fig. 5, a, n.seg). At this point the 

 nuclear membrane disappears and the segmentation - nucleus 

 divides by karyokinesis, forming a nuclear spindle which 

 becomes elongated until it stretches across the whole body of 

 the gametocyte (Fig. 5, a and b, ac.sp). The two daughter-nuclei 

 divide again in their turn, and in this way repeated nuclear 

 divisions follow one another in each gametocyte ; but those in one 

 individual take place independently of those in the other, and 

 are not synchronous (Fig. 5, c). The karyosomes of the primitive 

 nucleus are left free in the cytoplasm and are slowly absorbed. 

 As the nuclei multiply, their size, and that of the karyokinetic 

 spindles, diminishes until it reaches a minimum (Fig. 5, b and d). 

 Nuclear division then ceases, and the minute nuclei travel to the 

 surface of the body. The cytoplasm of the gametocyte now 

 breaks up into a number of small masses each centred round 

 one of the tiny nuclei. Each of the small nucleated bodies thus 

 formed is commonly termed a sporoblast, but should be dis- 

 tinguished as a primary sporoblast, or better still, as a gamete 

 (Fig. 6, a). The protoplasm of the gametocyte is not entirely 

 used up to form the gametes, but a surplus of residual protoplasm 

 is left over, termed the cystal residuum (" reliquat kystal," " Rest- 

 korper "), which serves for the nutrition of the sporoblasts during 

 their further development. In the residuum are found also a 

 certain number of degenerated nuclei (Fig. 6, r.p, r.ri), 



The next step is the conjugation of the gametes, which takes 

 place within the cyst. The cuticle which formed primitively the 

 body -wall of each gametocyte becomes dissolved, and the two 

 original individuals can no longer be distinguished, since the 

 gametes and other protoplasmic fragments derived from them 

 become intermingled. The gametes themselves now begin to 

 exhibit lively movements, the so-called " dance of the sporoblasts," 

 which gradually cease as they conjugate in pairs. It is probable 

 that in each pair one gamete is derived from one of the two 

 parent gametocytes, and the other from the other, but it is by no 

 means certain that this is always the case. The two conjugating 

 gametes unite completely to form a single zygote or definitive sporoblast, 



1 According to Cuenot the chromosomes are formed independently of the karyo- 

 somes, but it is more probable that, as in Coccidia (p. 216), their chromatin substance 

 is derived from a part of that which is stored up in the latter. The more recent 

 observations of Prowazek [25a] confirm this supposition. 



