334 Dr. F. Cohn on a new genus of the family of VolvocineaeCIj 



almost everywhere met^ and since no special establishment of 

 has ever been given^ it appears to me useful to examine the new 

 genus StephanosphcB7-a more minutely from the point of view, by 

 which the relationship of this as well as of the other Volvocinea 

 to plants will be made clear. I have also been led to consider 

 it advisable to give the description of this new Alga in a Journal 

 of Scientific Zoology, because zoologists alone have hitherto 

 taken an interest in the forms of the Volvocinece, and at present 

 appear unwilling to give up to the botanist this interesting 

 family, to which, however, as will be explained in the sequel, they 

 have no valid claim. I may remark, however, that I shall con- 

 fine myself here solely to Stephanosphara, and reserve for another 

 occasion the examination of the other genera, on which I have 

 collected some new material. 



V. Relation of the Volvocineae to Chlamydococcus. 



The most incontestable proof of the vegetable nature of all the 

 Volvocinea is furnished by their relationship to the genera Chla- 

 mydomonas and Chlamydococcus, the developuiental history of 

 which has been followed out in its most minute details during 

 the last few years in the researches of Von Flotow, Alex. Braun 

 and myself. The latter genus particularly, which, mingled 

 with Stephanosphofi^a, imparts a red colour to cavities in stones 

 filled with I'ain-water, has, as the most minutely investigated, 

 furnished the most information not only regarding the general 

 position of the Volvocinea, but also as to the import of the indi- 

 vidual portions of their organization. 



Dujardin indeed thought that the genus Chlamydomonas and 

 the closely allied Chlamydococcus ought to be separated from the 

 remainder of the Volvocinece, and that they should be embodied 

 in his Thecamonadice, nearly the same as Ehrenberg^s Cryptomo- 

 nadina ; but a more profound investigation, not only of the 

 structure but also of the history of development, teaches us that 

 Chlamydomonas [Diselmis, Duj.) possesses only external analogies 

 with Trachelomonas, while this form, as Ehrenberg already dis- 

 covered, exhibits the closest alliance to Gonium and Pandorina. 

 The relation of the colourless envelope to the enclosed green 

 globes, the position of the two cilia, which arise from the latter 

 and pass out through the former*, and lastly the laws of division 

 of the green cells inside the envelope, in powers of two, dis- 

 play themselves in exactly the same way in Chlamydococcus as 

 in the rest of the Volvocinece ; and the only distinction between 



* I have already mentioned this condition of the cilia in Stephano- 

 spheera ; it was detected by Focke in Pandorina, and was observed pre- 

 viously by Ehrenberg both in this and Volvox. 



