Dr. F. Cohn on a new genus of the famihj of Volvocinese. 403 



work (Verjungung, %cc., 279), with which my own observations 

 agree perfectly. The essential point in this is, that the contents 

 of the large cells of Hydrodictyon are transformed in two ways : 

 first, into a number of large moving spores, which are of globular 

 form, send out two cilia from a colourless point, only tremble 

 and jerk hither and thither within the parent-cell, and never 

 leave this ; after a brief swarming these attach themselves into a 

 network in the interior of the envelope and secrete a rigid mem- 

 brane which surrounds the whole ; in this manner they_, the ma- 

 crogonidia, become combined into a family of cells and grow into 

 a new net exactly like the original. Secondly, in other cells of 

 Hydrodictyon the contents are converted into a far greater num- 

 ber of smaller microgonidia, 30,000 to 100,000 of which are de- 

 veloped in one utricle ; these are spindle-shaped, possess four 

 cilia, move very actively and quickly, emerge singly from the 

 parent-cell into the water, and after a long movement pass into 

 a condition of rest^ without ever becoming united into a net- 

 shaped family of cells. 



Abstracting the differences which may be shown always be- 

 tween two genera, we detect the same law of development, that in 

 Hydrodictyon as in Stephanosphcera, the bi-ciliated, less nume- 

 rous macrogonidia arrange themselves into a family of cells 

 already within the parent-cell, according to the character of the 

 given conditions of the two genera, the cell-family being active 

 in the Volvocinece and immoveable in the Protococcacece ; while 

 the more numerous, more actively moving microgonidia with 

 four cilia leave the parent-cell and enter upon a metamorphosis, 

 the retrogradation from which to the normal type of the genus 

 has not been observed yet here, or indeed in the microgonidia of 

 any of the Algse. Such au undeniable agreement of the law of 

 development of Stephanosphcera with an undoubted plant like 

 Hydrodictyon, which testifies to a near relationship, would be in- 

 conceivable if the former were to be regarded as of essentially 

 different organization, — as belonging to quite another kingdom of 

 nature*. Thus the developmental history of Stephanosphaera 

 •also furnishes the most convincing proof of the vegetable nature 

 of this genus, and consequently of the Volvocinea generally. 



* Thuret has also observed in one of the Dictyotem, Cutleria multifida, 

 besides large swarming-cells which are developed to the number of eight 

 in a parent-cell and readily germinate, the formation of smaller, likewise 

 moving cellules, which originate exactly in the same way, only by often- 

 repeated division (to thirty-two?), and never germinate. Thuret regarded 

 the latter as analogous to the spermatozoids ; we should rather consider 

 them as a proof that a simultaneous formation of macrogonidia and micro- 

 gonidia occurs also in the higher forms of the marine Alga; (see Thuret, 

 I. c. vol. xiv. pi. .31, and vol. xvi. pi. 1). 



26* 



