96 



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 dicecious, i.e., either 

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

 generally protog}'nous, 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 



Fig. 24. — Volvox globator. (After Coiix.) 

 a. Balls of sperms ; b. immature ova ; c. ripe o\-a. 



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

 numerous (32-100 or more) slender spermatozoa, each with two cilia. 

 In V. globator their bundles may breal< 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 



