REPRODUCTION 185 



two individuals undergo a complete fusion within one test and en- 

 cyst. In Stephanosphaera pluvialis (Fig. 80), both asexual and sexual 

 reproductions occur, according to Hieronymus. Each individual 

 multiplies and develops into numerous biflagellate gametes, all of 

 which are alike. Isogamy between two gametes results in formation 

 of numerous zygotes which later develop into trophozoites. 



Anisogamy has been observed in certain Foraminifera. It perhaps 

 occurs in the Radiolaria also, although positive evidence has yet to 

 be presented. Anisogamy seems to be more widely distributed. In 

 Pandorina morum, Pringsheim observed that each cell develops asex- 

 ually into a young colony or into anisogametes which undergo sexual 

 fusion and encyst. The organism emerges from the cyst and develops 

 into a young trophozoite. A similar life-cycle was found by Goebel in 

 Eudorina elegc.ns 



The wood-roach inhabiting flagellates belonging to Trichonympha, 

 Oxymonas, Saccinobaculus, Notila and Eucomonympha, were found 

 by Cleveland (1949a-1951a) to undergo sexual reproduction when 

 the host insect molts. It has been observed that the gamete-forma- 

 tion is induced by the molting hormone produced by the prothoracic 

 glands of the host insect. The sexual reproduction of Trichonympha, 

 possessing 24 chromosomes, as observed and described by Cleve- 

 land, is briefly as follows (Figs. 81, 82): About three days before its 

 host molts, the haploid nucleus in the flagellate divides, in which 

 two types of daughter chromosomes (or chromatids) become sepa- 

 rated from each other: the dark-staining male gamete nucleus and 

 light-staining female gamete nucleus (Fig. 81, b-d); in the mean- 

 time, a membrane is formed to envelop the organism (b, d). When 

 the cytoplasmic division is completed (e-g), the two gametes "ex- 

 cyst" and become free in the host gut (h; Fig. 82, b). In the female 

 gamete, there appear "fertilization granules" (Fig. 81, h), which 

 gather at the posterior extremity (i), through which a fluid-filled 

 vesicle ("fertilization cone") protrudes (Fig. 82, a). A male gamete 

 (6) comes in touch with a female gamete only at this point (c), and 

 enters the latter (d-f). The two gamete nuclei fuse into a diploid 

 synkaryon (g, h). The zygote and its nucleus begin immediately to 

 increase in size, and undergo two meiotic divisions (i-k), finally giv- 

 ing rise to vegetative individuals (Fig. 81, a). 



Among the Sporozoa, anisogamy is of common occurrence. In 

 Coccidia, the process was well studied in Eimeria schubergi (Fig. 

 243), Aggregata eberthi (Fig. 246), Adelea ovata (Fig. 253), etc., and 

 the resulting products are the oocysts (zygotes) in which the spores 

 or sporozoites develop. Similarly in Haemosporidia such as Plasmo- 



