Dr. F. Cohn on a ncir genus of the family o/ Volvociuese. 325 



m the shape of the green primordial-cells themselves. I have 

 called them globes above ; properly they are always acuminated 

 to some extent, in the form of a pear, toward the periphery of 

 the envelope-cell, and they are imperceptibly attenuated to a 

 point here, from which two cilia pass out (fig. 1). These cilia 

 therefore arise from the primordial-cells inside the envelope- cell, 

 and they emerge freely into the water through minute orifices in 

 the latter : from the analogy with Chlamydococcus, I conjecture 

 that there is a separate passage for each cilium, so that the orifices 

 corresponding in each case to the primordial-cells are placed in 

 pairs, and all sixteen orifices occur in the equator of the envelope- 

 cell. Hence in the polar view the eight pairs of cilia go out 

 from the cii'cumference of the envelope-cell like elongated rays 

 (PI. VI. figs. 1, 3, 14). 



The primordial-cells moreover expand principally in the di- 

 rection of the axis peipendicular to the equatorial plane, so that 

 in the equatorial view they appear, not spherical, but rather 

 elliptical, or even sometimes stretched so considerably in this 

 direction, that they become cylindrical or almost spindle-shaped, 

 withoiit undergoing any remarkable enlargement on the other 

 axes (fig. 4 corresponding to fig. 3). If in this case the primor- 

 dial-cells are large and near together, they form in the equatorial 

 view a broad green zone inside the colourless envelope-cell, 

 filling up a more or less considerable portion of this (fig. 2), 

 while in the polar view they form only a circular wreath. In 

 some instances the proper green body of the primordial-cells is 

 only shortly cylindrical ; but it becomes elongated at both ends 

 into long beaks which rei^ch almost to the poles, and give each 

 primordial-cell something of the shape of the Closterium setaceum 

 figured by Ehrenberg (Infusionsth. vi. 9). In this case the 

 whole resembles a sphere surrounded by eight green bands 

 placed in meridians and swollen only in the equatorial region. 

 But even in this very frequently occurring, preponderating de- 

 velopment of the one dimension, the cilia of each primordial-cell 

 are sent out from the middle of its shorter axis, and when the 

 primordial-cells appear projected in a zone, in the equatorial 

 view, the motile cilia are visible only at four points of the diameter 

 (PI. VI. fig. 4). 



The primordial-cells are very frequently developed unequally 

 in the two hemispheres of the envelope-cell ; they are not then 

 divided into two equal halves by the equator of the envelope-cell, 

 but show themselves crowded principally into one hemisphere, 

 which they almost fill, and they reach almost to the pole thei'e, 

 while they occupy but a far smaller portion of the other, which 

 consequently appears in greater part colourless (fig. 5). In such 

 a case the priraordial-celfs almost touch with one end, while 



