9 6 



PROTOZOA. 



In V. globator the two kinds of reproductive cells are usually formed 

 in the same colony, the spermatozoa generally first. Technically, the 

 colony is usually a protandrous hermaphrodite. 



In V. aureus the colony is oftenest unisexual or dioecious, i.e., either 

 male or female. But it may be monoecious or hermaphrodite, and then 

 generally protogynous, i.e., producing eggs first. 



Whether in a hermaphrodite or in a unisexual colony, the sex cells 

 appear among the ordinary vegetative units ; the ova are distinguishable 



a 



FIG. 24. Volvox globator. (After CORN.) 



a. Balls of sperms ; b. immature ova ; c. ripe ova. 



by their larger size, the "sperm mother cells" divide rapidly and form 

 numerous (32-10x3 or more) slender spermatozoa, each with two cilia. 

 In V. globator their bundles may break up within the parent colony ; or, 

 as always in V. aureus, they may escape intact, and swim about in the 

 water. In any case, the ovum is fertilised by a spermatozoon, and, after 

 a period of encystation and rest, segments to form a new colony. 

 Occasionally, however, this organism, so remarkable a condensation of 

 reproductive possibilities, exhibits a parthenogenetic development of ova. 

 Here then we have an organism, on the border line between plant 



