OF THE PnTTOZOA. 125 



fact, only transitional stages. Tims, the ' still ' Protococcus-dQW. coiTesponds 

 to the common Protococcus coccoma (Kiitz.). "WTien the border becomes gela- 

 tinous, it resembles P. pulclier, and the small cells P. minor. The encysted 

 motile zoospore is the genus Oyges gi^anulum among the Infusoria, resembling 

 also, on the other side, P. tnrgidus (Kiitz.), and perhaps P. versatilis (Braun). 

 The zoospores divided into two must be regarded as a fomi of Gi/ges hipar- 

 titus, or of P. dimidiatus. In the quadripartite zoospores, with the secondary 

 cells arranged in one plane, we have a Gonium. That with eight segments 

 corresponds to Pandorina Moriim, and that with sixteen to Botryocystis 

 Volvox. A\Tien the zoospore is divided into thirty-two segments, it is a Uvella 

 or Syncrypta. ^Tien this form enters into the ' still ' stage, it may be re- 

 garded as a form analogous to Microhcdoa protogenita : this Algal genus is 

 probably, speaking generally, only the product of the Z7i'€7?«- division in the 

 Euglence or other green forms. The naked zoospores, finally, would represent 

 the form of a Monad, or of an Astasia ; the caudate variety approaches that 

 of Bodo. A critical and comparative consideration of the foregoing facts 

 would therefore appear to render untenable almost all the . principles which 

 modern systematists have hitherto adopted as the basis for construction of 

 their natui-al kingdoms, families, genera, and species." 



Cohn {op. cit. pp. 541, 542) makes the following general deductions : — 

 " 1. The Protococcus pluvialis is a plant, subject to an alternation of genera- 

 tions ; that is to say, the complete idea of the species is not exhibited in it 

 until after a series of generations. The forms of development which can be 

 possibly comprehended in the idea of the species do not in reality make 

 themselves apparent until a series of independent successive generations has 

 been gone thi^ough. 2. The individuals of each generation are capable of 

 propagating themselves in new generations. The individuals of the second 

 generation are among themselves, speaking generally, of equal value : as re- 

 spects the individuals of the parent generation, they are sometimes of equal 

 value with them, sometimes not. 3. If the secondary cells are not of equal 

 value with the parent-cells, a series of successive generations mu,st precede 

 the last generation, the individuals of which are again equivalent to the first 

 mother- cell. The number of these generations does not seem to be deter- 

 minate." By equivalent, the author means such individuals or generations 

 as correspond with each other in their essential, physiological, and organo- 

 logical relations, although they may differ in unessential properties, such as 

 colour, size, internal consistence, &c. Xon- equivalent are those generations 

 which in theii' stnicture and vital relations exhibit essential differences, such 

 as ' still ' and ' motile ' cells, and among these, again, their various forms, 

 and particularly those which are derived from a different mode of propa- 

 gation. 



Major von Flotow {Nova Acta Acad. Nat. Curios. 1844, p. 413), it is 

 right to state, remarked on the similarity of various forms of development 

 of Hcematococcus {Protococcus, Cohn) pluvialis with Infusoria, signahzing the 

 genera Chiloraomis, Cryptomonas, Gyges, Chlamydoiyionas, Pandorina, Clice- 

 toglena, and Chcatotyphla of Ehrenberg's system. 



Phytozoa, or structiuTS undistinguishable from them, constitute links in 

 the chain of still more marvellous transformations. Thus, Itzigsohn repre- 

 sents several in the history of the development of the Oscillatorieoe. For ex- 

 ample {J. M. S. 1854, p. 189) — " The filaments of OsciUaforia tenuis break up 

 into perfectly distinct joints, which, at first urceolate, soon become spherical. 

 The minute yellowish -green gonidia thus arising gradually increase in size, 

 become motile, and present in aU respects the aspect of Cldamydomonas.'" 

 These bodies " gradually enlarge ; a red eye-point becomes visible in them ; 



