VOLVOCINE^E. 65 



GENUS 40. EUDORINA. Ehrb. (1831.) 



Coenobium oval, involved in a common tegument ; cells green, 

 globose (16-32), enclosed within a single membrane, bearing 

 vibratile cilia, often "with a red spot (eye-spot), distributed 

 around the hyaline sphere at equal distances apart. Asexual 

 propagation in all the ccenobia, the cells of which are divided 

 into 16-32 parts, and soon evolved into new ccenobia. Sexual 

 propagation in all the ccenobia, the cells being converted into 

 motionless oospores enclosed in a narrow epispore, afterwards 

 becoming red. 



The most complete account we possess of the life-history of Eudorina 

 is that by H. J. Carter (Ann. Rat. Hist., Oct., 1858), of which the follow- 

 ing is a summary : Unable to recognise this organism in its simplest 

 form as a solitary cell, nor any stage of segmentation prior to the third 

 degree of duplicative subdivision into 16 cells, he commences from this 

 period. 



At this time, which we call the first stage, the Eudorina consists of an 

 ovoid green body, partially divided into the number of cells just men- 

 tioned, each of which is provided with a pair of cilia, which project 

 through a thin gelatinous envelope that surrounds the whole mass. It 

 is now about 1-llOOths of an inch long, i.e., not more than the diameter 

 of the Chlamy do coccus cell, and swims by means of its cilia, with the 

 small end foremost, and with a rotatory motion on its longitudinal axis, 

 as often from right to left as from left to right. An eye-spot is also 

 present in each of the four anterior cells, but seldom visible in the rest 

 at this period. 



As development progresses each cell is provided with a spherical, 

 translucent utricle, an eye-spot midway between the cilia and the oppo- 

 site end of the cell, a contractile vesicle at the base of the cilia, and the 

 pair of cilia themselves. 



During the second stage each of the cells again undergoes duplicative 

 division, and the whole organism becoming larger, they are separated 

 from each other, and being no longer subject to compression, become 

 sphaerical and enclosed respectively within distinct transparent capsules. 

 The Eudorina is now six times as long as in the first stage, and contains 

 32 green cells, whicb are evidently situated between two large ovoid, 

 colour'ess, transparent cells, one of which bounds a similarly shaped 

 cavity in the centre of the Eudorina, and the other is the original cell 

 wall, round which again is the newly secreted envelope. Thus we see 

 that the Eudorina is derived from a simple (daughter) cell, and that its 

 green cells have resulted from a duplicative subdivision of the green 

 matter which lined the cavity of this cell. Arrived at this state, which 

 we shall see is that of maturity, we also observe that the posterior part 

 of the envelope becomes crenulated, apparently from flaccidity. 



After this, however, it again presents another phase, which may be 

 called the third, or last, stage of development. Here each cell again 

 undergoes a rapid duplicative subdivision into 16 or 32 cells, which, in 

 the group, assume a more or less oblong figure respectively, and thus the 

 Eudorina's length is increased to 10 times that of its first stage. Tbe in- 

 ternal structure now gradually breaks clown before the external envelope, 

 when for a short time the groups may be seen swimming about the cavity 

 thus formed, till at last the envelope bursts and they become liberated. 

 What becomes of them afterwards he could not state from observation, 

 but the green cells having been greatly reduced in size by the latter sub- 



