244 BOTANY. 



separated from Pandorina. If the two genera are to be 

 separated from Pandorina there can be but little doubt that 

 their position must be in the very lowest part of the Oophy- 

 ta. Such a position would indicate what is probable on 

 other grounds also, that the divisions Zygophyta and Oophy- 

 ta lie side by side as two divergent systems, and that in 

 their lowest members they almost, if not entirely, coalesce.* 

 324. Volvox globator is a hollow spherical colony of uni- 

 cellular algae, having a diameter of .5 to .8 mm (.02 to .03 

 inch). Each individual of the colony is a flask-shaped cell 

 of green-colored protoplasm, bearing two cilia upon its 

 pointed extremity, and surrounded by a hyaline gelatinous 

 envelope. These individuals are arranged so as to form a 

 spherical surface, their hyaline envelopes being in contact 

 with one another, and so placed as to bring the pointed ends 



of the green masses, with their 

 cilia, to the surface. The 

 sphere is thus made up of 

 closely approximated individ- 

 uals, which dot its surface, 

 and whose cilia give to the 

 whole colony a hairy appear- 

 ance. The movements of the 

 Pig. 164. Voivox globator. a, sperma- cilia give to the sphere a ro- 



tozoid. X 800. b, oogonium, with sper- , , . i i TI 



matozoida surrounding the oosphere, X tary motion, which IS USUaily 



one of progression also. 



325. The sexual reproduction of Volvox takes place in 

 this way : some of the cells in a colony undergo conversion 

 into spermatozoids, which are elongated club-shaped, and 

 provided with two cilia (a, Fig. 164) ; other cells of the same 

 colony, or of different colonies, become greatly enlarged into 

 oogonia, consisting of an outer hyaline coat enclosing an 

 inner rounded mass of dense and granular protoplasm (b, Fig. 

 164). Upon the escape of the spermatozoids they penetrate 

 the cavity of the colony (into which the oogonia have now 

 pushed), and there coming in contact with the oogonia, they 



* It will not do violence to any laws of classification, based upon 

 the general theory of evolution, to propose that Volvox, Eudorina, 



