402 Dr. F. Cohn on a new genus of the family 0/ Volvocinese. 



has very recently given us most excellent representations of this 

 phsenomenon, to which I refer every one who may wish to ac- 

 quire a clear idea of this remarkable mode of propagation of the 

 Algae and aquatic Fungi*. Yet to be warranted in deciding this 

 question, it is indispensable to make a direct and unprejudiced 

 observation at least of the most important phsenomena, which is so 

 much the easier to effect, that, with the exception of the Oscilla- 

 toriea, Nostochinea and Conjugatce, almost all the Algse propa- 

 gate by swarming-spores throughout the whole year. An inde- 

 pendent examination is here the more indispensable to every one 

 who wishes to acquire an unprejudiced opinion as to the orga- 

 nisms standing on the limits between the animal and vegetable 

 kingdoms, since the phsenomena here in question are totally 

 different from anything elsewhere known in the vegetable king- 

 dom, and must be regarded as sui generis.^ The macrogonidia of 

 StephanosphfEva themselves also agree perfectly in structure and 

 movement with the swarming-cells bearing two cilia which Na- 

 geli has represented of Tetruspora (Einzell. Algen. t. ii. C./), of 

 Characium {I. c. t. ii. A. /;), or of Apiocystis (t. iii. D. b) ; only 

 the common enveloping cell and the combination into families 

 of cells, which elsewhere occur merely in immoveable forms of 

 Algse, have not previously been observed in swarming-cells, and 

 must be regarded as specific characters of the Volvocinea, without 

 this organization standing in any contradiction to their vegetable 

 character. 



The developmental history of Stephanosphcera is especially de- 

 cisive for the position of the Volvocinece, because of the essential 

 agreement it exhibits with another organism as to the real nature 

 of which no doubt has ever been raised. 



One of our most widely diffused freshwater Algse, Hydrodictyon 

 utriculatum, is composed, as is well known, of large utricular 

 cells, which are arranged reticularly in such a manner that three 

 or four always meet in a point, and five or six bound each poly- 

 gonal space. The green contents lining the walls of the indivi- 

 dual cells, in which a great quantity of chlorophyll-utricles are 

 imbedded, are transformed in the propagation into a very large 

 number of swarming-cells, the structure of which was misunder- 

 stood until very recently, and was first revealed by the masterly 

 history of its development by Alex. Braun in his often-cited 



* Compare especially my drawing of the microgonidia of Stephanosphcera 

 (fig. 19) with the figures which Fresenius has given of the swarming-spores 

 of Chcetophora (zurControverse iiber die Verwandl. von Algen inlnfusorien), 

 or Thuret at pi. 16. fig. b, pi. 18. figs. 6, 10 & 11, pi. 19. fig. 3, pi. 21. 

 fig. 3, of his treatise above cited. See also " Sur les organes rej)roducteurs 

 des Algues," par MM. Derbes et Solier, * Ann. des Sc. Nat.* 3 ser. xiv. 

 pi. 33, on Draparnaldia. 



