160 GENERAL HISTORY OF THE INFUSORIA. 



been able to recognize tliis organism in its simplest form (that is, as a solitary 

 single cell), nor any stage of its segmentation prior to the third degree of du- 

 plicative subdivision (that is, into 16 cells, when the mother-coverings have 

 di^opped off), I must begin from this period. 



" At this time, Avhich we will call the first stage, the Eudorina consists of an 

 ovoid green bod}^, partially divided into the number of cells just mentioned, 

 each of which is provided with a paii* of cilia which project through a thin 

 gelatinous envelope that surrounds the whole mass. It is now in its smallest 

 size, about 5-5400ths of an inch long, that is, not more than the diameter of 

 the Chlmnydococcus-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 ceUs, but seldom visible in the rest at this period. 



" As the development progresses and the Eudorina increases in size, the di- 

 vision becomes complete, and each cell, in addition to the granular mucus and 

 chloro^Dhyll which line its interior, may now be seen to be provided internally 

 Avith a spherical translucent utricle (which is the nucleus), an eye-spot situ- 

 ated peripheric ally and riiidway between the cilia and the opposite end of the 

 cell, a contracting vesicle at the base of the cilia, and the pair of cilia them- 

 selves. Each pair of cilia passes out through a single channel in the gelati- 

 nous ceU or envelope, which has now become much thickened — and thus their 

 movements are Kmited u^d to this ]3oint, — while a defined line internally marks 

 the boundary of the original cell- wall, through which, of course, the cilia also 

 pass. 



*' Dui^ing the second stage, each of the ceUs again undergoes duplicative 

 division (the nuclei having been doubled previously) ; and the whole organism 

 becommg larger, they are separated from each other, and being no longer sub- 

 ject to the compression which, with the lines of fissiparation tending towards 

 the centre of the ellipse, and their confined position, induced a more or less 

 conical and polygonal shape, now become spherical and enclosed respectively 

 within distinct transparent capsules. The Eudorina is now 30-5400ths of an 

 inch long, and contains thirty-two green cells, which are evidently situated 

 between two large, ovoid, colourless, 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, — while 

 the green cells are further fixed in theii' respective positions by the passage of 

 their ciha through the two latter, both original cell-wall and envelope. Thus 

 we see that the Eudorina is derived from a simjDle (daughter-) cell, and that 

 its green cells have resulted from a duplicative subdiv-ision of the green matter 

 Avhich lined the cavity of this cell. Arrived at this state, which we shall pre- 

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

 envelope becomes crenulated, apparently fi^om flaccidity. 



" After this, however, it again presents another phase, which maybe called 

 the third or last stage of development. Here each cell again undergoes a rapid 

 duplicative subdivision into sixteen or thirty-two cells, which, in the group, 

 assume a more or less oblong figui'e respectively ; and thus the Eudorina's 

 length is increased to 50-5400ths of an inch. The internal structure now 

 gradually breaks down before the external envelope, when for a short time 

 the groups may be seen swimming about the cavity thus formed, tiU at last 

 the envelope bursts and they become liberated. AVhat becomes of them after- 

 wards, I cannot state from observation ; but the green cells having been greatly 

 reduced in size by the latter subdivisions, it is probable that many of the 

 groups, if they do not form new individuals, sooner or later become disinte- 

 grated, and the Eudorina thus eventually perishes. 



