THE MALARIAL PARASITE 183 



as they are formed begin to execute vigorous lashing move- 

 ments (fig. 39, -D). At the same time the body of the micro- 

 gametocyte contracts till it is scarcely more than half its 

 original diameter. While these changes are in progress the 

 nucleus has broken up into eight pyriform or oval masses 

 surrounded by fine granules of chromatin. The pyriform 

 masses are composed of plastin containing a certain amount 

 of chromatin, and are therefore karyosomes. At first they lie 

 among the melanin granules in the centre of the cytoplasm 

 (fig. 39, C) but soon travel to the periphery of the gametocyte, 

 and a single karyosome with a number of surrounding chromatin 

 granules enters each of the long hyaline protoplasmic processes. 

 The last named are then set free as active filiform microgametes, 

 which wriggle away actively in all directions. In each micro- 

 gamete the karyosome occupies the centre and the chromatin 

 granules are strung out along the length of the rest of the body 

 (fig. 39, E). The remainder of the microgametocyte, contain- 

 ing the whole of the pigment granules, is left behind as residual 

 protoplasm and gradually disintegrates. As the number of 

 karyosomes is usually greater than the number of micro- 

 gametes formed, some of the former are left behind in the 

 residual protoplasm. The next step is the fertilisation of 

 the macrogamete by the microgamete. The former puts forth 

 a conical process of protoplasm, or "cone of reception," from 

 that part of the surface nearest to the nucleus, and as soon as 

 a microgamete touches this cone it adheres to it by one of its 

 extremities and is very rapidly absorbed into it, till only about 

 half of its length remains outside, still continuing to perform 

 lashing movements (fig. 39, F). After a short time the whole 

 body of the microgamete is drawn into the macrogamete, and 

 its entry is accompanied by violent streaming movements 

 of the cytoplasm, which slow down and cease in about ten 

 minutes' time, when the female nucleus is found to be situated 

 in the centre with the male nucleus fitted against one side of 

 it like a cap. The two nuclei remain distinct from one another 

 for some little time, but eventually fuse together to form a 

 single fertilisation nucleus or synkaryon. The single cell 

 formed by the union of the micro- and the macrogamete is of 

 course a zygote, comparable in all essential respects with the 

 zygote formed by the union of two gametes in Monocystis. 

 In the malarial parasite the zygote elongates, assumes a 



