124 GENEEAL HISTOEY OF THE nfEUSOEIA. 



50), These encysted spores resemble Chlamydomonads, and are called * Pro- 

 toccocoid ' cells or globules, from thek homology -^ith the encysted cells of 

 Protococcus. 



Occasionally, instead of one or several of the individual gonidia of a com- 

 pound organism being encysted, the process ensues with a gonidium deve- 

 loped by fission into macrogonidia, and the whole mulberry or Uvtlla-^e 

 mass becomes surrounded by a rigid envelope, either pretty closely applied, 

 or separated by an interspace. 



Examples of the encysted condition ^\ill occur in the followdng account of 

 the several groups of Phytozoa ; it sufiices at present to say that Prof. Wil- 

 liamson and others have pretty clearly shown that VoJvox aureus is only the 

 encysted or ' still ' form of V. yJohator, that Cohn has discovered the cysts of 

 StejihanosjjJicera, Gonium, and Eudonna, and Henfrey those of Pandorina. 



The after-history of the encysted spores of Phytozoa has not yet been 

 elucidated : we have above referred to Cohn's researches upon it ; but they 

 are too indefinite to supply any positive information. The act of conjugation 

 is common with many of the lower Algae, but has not been witnessed among 

 the Phytozoa. 



Phases of Beixg axd Alternation of Geneeation in Phytozoa. — From 

 the preceding accoimt of Phytozoa, it is evident that those best known exist 

 under a considerable variety of form — in other words, present several phases 

 of existence, or, viewed in relation -svith a prevailing hypothesis, exhibit 

 an alternation of generation. The whole history of any Phytozoon is com- 

 prehended m the cycle of changes which the organism passes through ; yet, 

 under any transformation, it is the self- same being, and its existence may 

 be said to extend from its most perfect through all intermediate phases imtil 

 the like degree of perfection is again attained. As happens in alternation 

 of generations among other organized beings, the transition may not be 

 direct and simjDle, but intermediate phases may reproduce themselves, and 

 these again develope into other forms of existence, as accessory or collateral 

 and usually imperfect cycles. 



Perhaps the metamorphoses in question are most striking in Euc/Ience ; for 

 the contrast between the actively- mo^T^ng, contractile, ever- changing being 

 in one phase of existence, and the encysted, ' Protococcoid,' spore-like and 

 motionless condition mth a rigid unvarying outline, is so remarkable as to 

 give colour to the hypothesis of the convertibiHty of animal into vegetable 

 life, or of the transformation of animals into plants. It is not our intention 

 at present to give illustrations of the vailing phases in the life of Phytozoa 

 involved in the process of fission, or of a duplicative multipHcation under its 

 various forms. However, other more extended instances of transformation 

 require to be noted, as observed by various microscopists, — although, it may 

 be, some errors have crept in, from the difiiculty of tracing the relation and 

 succession of the different phases of being. 



As a veiy good example of the wide and varied range of existence enjoyed 

 by most Phytozoa, we may adduce the Protococcus pluvialis (XIX. 20-31), 

 of which the industry and perseverance of Prof. Cohn have obtained for us 

 so complete an account. According to the researches of this eminent natu- 

 ralist, the simj)le plant in question, in its motile and still conditions, assumes 

 the form and characters of many microscopic organisms presumed to be, and 

 described by Ehrenberg and others as, distinct existences. To quote from 

 Cohn's memoir {R. S. p. 559), " We see that a single species, omng to its 

 numerous modes of propagation, can pass thi'ough a number of very various 

 forms of development, which have been either erroneously arranged as distinct 

 genera, or, at least, as remaining stationary in those genera, although, in 



