Volrocew 



1ST 



antherozoids and the latter developing into eggs. In V. aureus, which is the 

 most abundant European species, 16 or 32 antherozoids are formed in a 

 bundle by the division of the contents of an androgonidium, but in V. 

 (jlobator and other species as many as 128 are often formed. By the 

 conversion of the mother-cell-wall into mucilage the antherozoids are at 

 first set free in compact circular bundles, and are arranged with their long 

 axes all parallel. Each antherozoid is an elongated cell, pointed at one end 

 and rounded at the other, and the paired cilia may be inserted terminally 

 (V. aureus) or laterally (V. globdtor). In the male colonies of V. sperma- 

 tosphwra, in which all the cells form sperm-bundles, Powers has observed 

 as many as 65,536 antherozoids (or sperms) all maturing at the same time 

 in one cosnobium. The gynogonidia are usually few in number, averaging 

 6 in the colony in V. aureus and 30 in V. globator, but in V. perglobator 



Fig. 109. A C, Volvox (jlobator (L.) Ehrenb. A, section of the peripheral region of colony 

 showing a single cell ; B and C', surface views, showing (in C) the broad protoplasmic con- 

 nections between the cells. D, Volvox aureus Ehrenb., median section through part of 

 colony. /, inner membrane of wall ; o, outer membrane ; s, special layer of wall ; m, mucus ; 

 ml, middle lamella ; p, protoplast. Very highly magnified (after A. Meyer). 



from 300 to 400 have been seen in one coenobium. They develop into 

 globular oospheres, which while still unfertilized attain a diameter of over 

 90 /u, in V. W&ismanniana. Self-fertilization is said to take place in V. 

 globator, but this is not the case in several of the other carefully investi- 

 gated species. According to Overton ('89) each female colony of V. aureus 

 has a ' polar plateau,' a slightly raised circular area of the firm limiting 

 investment, situated at the posterior pole and free from vegetative cells. 

 The polar plateau is about 42 //, in diameter, and is believed by Overton to be 

 the point of entrance of antherozoids into the colony. 



