VolvocedB 



177 



symmetrically arranged, blunt processes (fig. 107 A and B). In contrast to 

 the cell-disposition of Gonium, the cilia of adjacent cells project alternately 

 upon either face of the plate. This flattened form cannot therefore have had 

 an origin from Gonium, but has most likely originated from Eudorina by 

 a compression of the colony. The presence of the 'caudal' lobes of the 

 enveloping mucus also supports this view since these are sometimes developed 

 (as posterior mamillate projections), but to a less extent, in the more ellipsoid 

 colonies of Eudorina 1 . 



In Volvoas, which is the most highly developed genus of the Volvocetv, the 

 ccenobium ranges from 200 to 2500 p in diameter, consisting of a large number 

 of Chlamydomonadine cells arranged in a single peripheral layer within a 

 globose or ovoid mucous investment. The coenobium is to a great extent a 

 hollow sphere in its later life, although in the younger stages much of the 



Fig. 105. Eudorina elegans Ehrenb. A , normal adult colony, x 475 ; /?, young daughter- 

 colony formed by division of contents of mother-cell, x 730. C E, development of 

 antherozoids from mother-cell ; F, antherozoids (after Goebel). 



interior is occupied by a watery mucus. The number of cells varies from 

 about 2000 (rarely as few as 200) in V. aureus to rather more than 50,000 in 

 V. Rousseletii (G. S. W., 10). In some species the cells are joined by distinct 

 protoplasmic connections, which in V. globator are very broad (fig. 109 C), but 

 in others so far as can be ascertained there are no such connections. The 

 spacing of the cells on the periphery of the colony is also very variable, the 

 extremes being in V. perglobator Powers and V. Rousseletii G. S. West. In 



1 Since both Chodat ('02) and Conrad ('13) have described the regular presence of posterior 

 mamillations of the enveloping mucus, it would appear probable that there are two distinct races 

 of Eudorina. The colonies which possess these posterior lobes are markedly ellipsoid or even 

 ovate-ellipsoid, whereas the colonies without such lobes are almost globose. The author has 

 examined thousands of colonies from the British Islands, N. America, India and Australia, and 

 in all cases they were almost spherical with no trace of posterior mamillations. 



W. A. 12 



