VOLVOX AND ITS ALLIES. 



245 



bury themselves in the hyaline envelope, and finally pene- 



trate and become fused into the oosphere (b, Fig. 164). A 



thick wall now forms upon the fertilized oosphere, and it 



becomes transformed into an oospore. Thus we have in 



these plants the transformation of an 



individual of the colony into an oogo- 



nium and oosphere, and the subse- 



quent fertilization of the latter by 



spermatozoids, which are themselves 



fractional parts of other members of 



the colony. 



326. The relationship of the low- 

 er Oosporeae with the lower Zygo- 

 sporeae, as indicated by Volvox and 

 Pandorina, is further shown by the 

 position of Sphceroplea, an undoubted 

 relative of the Confervacece (Clado- 

 phora, etc.). Sphceroplea is a free, 

 unbranched, filamentous alga, com- 

 posed of long cells joined end to end 

 (A, Fig. 165). It produces oospheres 

 in some of its filaments, each cell 

 producing several (B, Fig. 165). 

 While these are forming in one set of 

 filaments, in another the protoplasm oogoma; m and k, oospneres 



, , . , if-i i it the instant of fertilization ; 



becomes broken up into a multitude , fertilized oospb. res, now 



of elongated, bi-ciliate spermatozoids 



(O and 0, Fig. 165); these escape 



through lateral openings in the cells, ^ n lj ? t f t n ? ck 



which are formed by the absorption lose ' -f,.zoospore (vegetiih-e 



,. J . ,. V . zoogonidium). f, oosphere in 



Of a part of the Wall, and then SWim- the act of being fertilized by a 

 11 t ii 11 Q -, spermatozoid, . G. spermato- 



ming through the water they find zoids. -After (Ersted. 

 their way to corresponding openings in the walls of the 



and their allies in the Oosporeae, and Pandorina, and its allies in the 

 Zygosporeae, be placed in a common class Zoosporeae. This class 

 would thus have two branches, one in the division Zyjfosporeae, and 

 the other in the Oosporeae. Such an arrangement would indicate 

 the evident relationship of the plants under consideration better than 

 any yet proposed. 



