EUDORINA AND PLEODORINA I95 



however, strongly differentiated. The female gametes 

 are very much like the ordinary vegetative cells except 

 that they soon lose their fiagella. They are not set 

 free from the colony in which they are formed, which 

 scarcely differs in appearance from a vegetative colony. 

 The male gametes, on the other hand, are formed by 

 division of each cell of a vegetative colony into 64 

 cells (male gametes) forming a plate, and each of 

 these is long and narrow, tapering at the end, the 

 green chloroplast being represented only by a yellow 

 coloration at the hinder end.^ The plate of male 

 gametes swarms out as a whole, hke a coenobium, 

 but soon breaks up into its constituent gametes, each 

 of which is capable of seeking out and conjugating with 

 a female gamete, the process resulting in the forma- 

 tion of a zygote. Here we have the third character 

 of sex differentiation — a difference in structure between 

 the two gametes, as well as the difference in size and 

 activity seen in Ohlamydomonas monadina and to 

 some extent in Pandorina. It is to be noted that the 

 male gamete has suffered reduction in its nutritive 

 equipment, i.e. its chloroplast, as well as in size. 



In Pleodorina illinoiensis (Fig. 26, A) the coenobium is 

 almost identical with that of Eudorina, except that 

 (usually) four of the cells at the front end of the 

 coenobium (which is often elliptical in shape) are 

 smaller than the others. When division occurs to 

 form new coenobia these four smaller cells do not 

 divide Uke the others ; and they remain behind, 

 eventually dying, when the daughter ccenobia escape. 

 Here we have the first indication, in this series of 

 organisms, of the appearance of a soma or mortal 



' The male gametes of Endorina are very much like those of Volvox 

 (see p. 200 and Fig. 28, ^D). 



