Dr. F. Cohn on a new genus of the family of Volvocinese. 347 



shaped and acuminated at both ends, bright green in the middle, 

 and run out into a colourless beak at each end, on the whole not 

 unlike young Euglena, without trace of an envelope-cell; the 

 extremity which goes first in their swimming bears delicate cilia ; 

 the number of the cilia is four (fig. 19). When the microgonidia 

 reach the water they move most actively in all directions, and in 

 a short time all the corpuscles emitted from an envelope-cell are 

 scattered and disappear in the wide surface of the drop of water. 

 I have not been able to make out what becomes of the micro- 

 gonidia subsequently, since they are ordinarily decomposed on 

 the object-holder after a brief swarming ; but it may be con- 

 jectured that they also serve for propagation, and probably pass 

 into a condition of rest. At least the latter has been observed in 

 the microgonidia of Chlamydococcus pluvialis by Alex. Braun and 

 myself : the history of the development of the latter agrees wholly 

 with those of the Stephanosphcera ; they originate also by the 

 division of the primordial-cell in a higher power, are distin- 

 guished by their minute size and more active, peculiarly Infu- 

 sorioid movement, and never develope an envelope-cell during 

 their movement. The microgonidia of both therefore are true 

 primordial-cells ; that is, primordial-utricles resembling cells, or- 

 ganized exclusively of coloured protoplasm, without any cellular 

 membrane*. The only distinction between them is, that the 

 microgonidia of Chlamydococcus, like their macrogonidia, possess 

 two cilia, while in those of Stephanosphoira I observed four. 

 That the microgonidia of Stephanosph(Bra correspond perfectly 

 in morphological respects to the macrogonidia, and only depend 

 upon a higher power of division, is proved by a case in which 

 seven out of the eight primordial- cells in one envelope-cell were 

 broken up into microgonidia, while one divided merely into eight 

 secondary-cells ; the latter were developed as macrogonidia and 

 formed a connected wreath surrounded by an envelope-cell, 

 which rolled slowly about in the parent-envelope, surrounded 

 by the swarm of free, rapidly moving microgonidia (fig. 18 a). 

 Alex. Braun has also observed a formation of microgonidia in 

 Chlamydornonas obtusa ; probably all the rest of the Volvocinece 

 have a formation of small isolated microgonidia which become 

 free, as well as the ordinary propagation by large macrogonidia 

 arranged in families of cells. 



* In tfiese, and generally speaking in most swarming-cells of Algae, we 

 have structures which in their development and independent individualiza- 

 tion, their vital processes and their mode of movement, behave exactly as 

 cells, but are composed solely of cell-contents, without cell-membrane ; a 

 proof that in the vegetable kingdom even the definition of the cell must be 

 in many cases conceived in a more extended sense than might be assumed 

 from the schemata of our manuals. 



[To be continued.] 



