GENERAL ORGANIZATION 759 



with one another, do not fuse. These binucleate amoeboid bodies, which 

 are about 11 microns in diameter, escape into the intestine of the worm 

 and proceed to develop, so that auto-infection has to be recognized. 

 The two nuclei of each amoeboid body divide to form a total of four nuclei, 

 two of which migrate to the periphery and, together with some of the 

 cytoplasm, form the capsule which develops, while the two remaining 

 nuclei increase in size. The cytoplasm within the capsule, which increases 

 in size, divides to form two cells, while by a further division four cells are 

 produced, two of which are larger than the other two. By further 

 divisions, which proceed somewhat irregularly, eventually eight small cells 

 and eight large cells are formed. These are gametes, and it appears that 

 certain reduction bodies are discharged from their nuclei. The gametes 

 unite in pairs (anisogamy), forming eight zygotes within the cyst. Each 

 zygote, which, in addition to the nucleus, contains a granule of what 

 appears to be residual chromatin, develops into a three-rayed spore. 

 By a series of nuclear divisions, two, four, six, and then seven nuclei are 

 formed. Three of these migrate to one end of the cytoplasmic mass, 

 where they become the capsulogenous cells from which the polar capsules 

 are formed, three of them pass to the opposite pole and form the cells 

 which give rise to the three-rayed spore envelope, while the remaining 

 nucleus divides many times till twenty-seven nuclei are formed. Of these 

 nuclei, twenty-four are nuclei of sporozoites and three the residual nuclei 

 of the spongioplasm, in the substance of which the twenty-four sporozoites 

 are eventually developed. 



In this development it will be seen that the union of the sporozoites is 

 not a syngamic process, as the nuclei remain distinct. When the nuclei 

 divide to form four nuclei, two of the nuclei, together with some of the 

 cytoplasm, form the cyst wall, which encloses the rest of the cytoplasm 

 containing two nuclei. Eventually sixteen gametes are produced from 

 these two cells, and it seems probable that eight of these, which are macro- 

 gametes, are derived from one sporozoite, while the eight microgametes 

 are formed from the other. Finally, there is a spherical cyst containing 

 eight zygotes. When each zygote has completed its development, the 

 spherical cyst contains eight closely packed spores. The worm Tubifex 

 tubifex appears to harbour at least four species of Triactinornyxon. 

 T. ignotum. Stole, 1899, has eight sporozoites in each spore; T. legeri 

 Mackinnon and Adam, 1924, has twenty-four; T. sp. Leger, 1904, has thirty- 

 two; and T. mrazeki Mackinnon and Adam, 1924, has more than fifty. 

 The cycles of development of these species resemble one another very 

 closely, and it appears probable that, apart from the difference in 

 shape of the spores, the members of the other known genera of 

 Actinomyxidiida develop in a similar manner. Granata (1925), who 



