REPRODUCTION 



145 



of its nuclear material, fuses with the other and the zygote thus 

 formed, encysts. In Stephanosphaera pluvialis (Fig. 70), both 

 asexual and sexual reproductions occur, according to Hieronymus, 

 Each individual multiplies and develops into numerous biflagel- 

 late 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, Gregari- 

 nida (Lankesterella, Fig. 174; Schizocystis, Fig. 185), etc. It per- 



Wm ^ 



Fig. 69. Sexual fusion in Copromonas subtilis, X1300 (Dobell). 



haps occurs in the Radiolaria also, although positive evidence has 

 yet to be presented. Anisogamy seems to be more widely dis- 

 tributed. On the whole, the differences between the micro- and 

 macro-gametes are comparable with those which exist between 

 the spermatozoa and ova of the Metazoa. The microgametes are 

 motile, relatively small and usually numerous, while the macro- 

 gametes are usually not motile, much more voluminous and fewer 

 in number (Fig. 71). In Chlamydomonas monadina (Fig. 90), ac- 

 cording to Goroschankin, the two gametes come in contact at the 

 anterior end where the membranes become dissolved and the 

 contents of the microgamete stream into the macrogamete. A 

 new shell is then secreted around them. Later the shell becomes 

 swollen and the organism multiplies into 2, 4, or 8 swarmers 

 which in turn develop into the trophozoites. In Pandorina morum 

 (Fig. 72), Pringsheim observed that each cell asexually develops 

 into a young colony (a, h) or into anisogametes (c) which undergo 

 sexual fusion {d-g) and encyst {h). The organism emerged from 

 the cyst, develops into a young trophozoite {i-m). A similar life- 

 cycle was found by Goebel in Eudorina elegans (Fig. 73). 



Among the Sporozoa, anisogamy is of common occurrence. In 



