REPRODUCTION 



151 



secreted by the other. Kuhn, Moewus and Wendt (1939) recognized 

 "hormones," and named them, termones (sex-determining hor- 

 mones), anderotermone (male-determining hormone) and gynoter- 

 mone (female-determining hormone). 



In a few strains or species of Chlamydomonas, sexual fusion is 

 found to take place among the gametes that develop within a single 

 clone. Moewus considers in these cases there exist two types of 

 gametes in a clone. However, Pascher, Pringsheim, and others ob- 

 tained results which seem to indicate that there is no physiological 

 or sex differentiation between the fusing gametes. In the much- 

 studied Sporozoa, for example, Plasmodium, the two gametes are 

 both morphologically and physiologically differentiated, and sexual 

 fusion always takes place between two anisogametes. 



Fig. 73. Sexual fusion in Coprompnas subtilis, X1300 (Dobell). 



The isogamy is typically represented by the flagellate Copro- 

 monas suhtilis (Fig. 73), in which there occurs, according to Dobell, 

 a complete nuclear and cytoplasmic fusion between two isogametes. 

 Each nucleus, after casting off a portion of its nuclear material, 

 fuses with the other, thus forming a zygote containing a synkaryon. 

 In Stephanosphaera pluvialis (Fig. 74), both asexual and sexual re- 

 productions 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 niorum (Fig. 75), Pringsheim observed that each cell de- 

 velops asexually into a young colony (a, b) or into anisogametes (c) 

 which undergo sexual fusion {d-g) and encyst (/i).-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. 76). 



