180 



Volvocinea? 



Reproduction occurs in Pandorina by zoogonidia which are precisely 

 similar to the mature cells of Chlamydomonas (Dangeard, '00). They arise 

 by the longitudinal division of the contents of the mother-cell, and each one 

 secretes in addition to its own membrane a mucous outer coat which 

 ultimately forms the common investment of the colony. Schroder ('98) also 

 observed zoogonidia in Pandorina, and states that they lose their cilia, 

 vacuoles, and pigment-spot before dividing to form a new colony. 



Gamogenetic reproduction has been observed in all the genera except 

 Platydorina and Stephanoon. In Gonium it is by the fusion of isogametes 

 which may arise from any cell of the coenobium. In Pandorina the gametes 

 are formed as in Gonium, but they exhibit considerable variability in size. 



Fig. 108. A, C, and D, Volvox aureus Ehrenb. A, monoecious sexual colony, x 210 ; C, two 

 antherozoids (after Klein) ; D, ripe oospore, x 475. B, ripe oospore of Volvox ylobator (L.) 

 Ehrenb., x475. a, androgonidia ; an, antherozoid ; <j, gynogonidia. 



They fuse in pairs, generally a smaller (male) gamete with a larger and 

 more sluggish (female) gamete (fig. 92 C}. In Pleodorina, Eudorina, and 

 Volvox the differentiation of the sexual cells is altogether more complete, 

 although it is in Volvox that the greatest differentiation is found. In this 

 genus there are asexual (i.e. purely vegetative) colonies and sexual colonies, and 

 the latter, which sometimes possess parthenogonidia also, may be monoacious 

 or dioecious. There are in the sexual colonies certain reproductive cells 

 which become either androgonidia or gynogonidia, the former giving rise to 



