OF THE PHYTOZOA. 155 



plane as a disc formed hy a collection of green globules, at others, on their 

 edge, looking little more than a green line. 



At length the mother-cell ruptm-es, and, the mucous envelope having dis- 

 appeared at a previous stage (XIX. 37), the yoimg colony escapes into the 

 suiTounding water, moves fi'eely about, and commences an independent ex- 

 istence. These young forms have usually a diameter of j^'". Supposing, 

 which is very probable, that a young Gonium after 24 hoiu's is capable of 

 development by fission, it follows that under favoui'able conditions a single 

 colony may on the second day develope 16, on the third 256, on the foiu'th 

 4096, and at the end of a week 268,435,456 other organisms like itself. 

 This calculation sufiiciently explains the extremely rapid multii)Hcation of 

 these organisms, coloming a collection of water, floating on its surface as a 

 scum, or settled in bad weather as a filmy stratum at the bottom. 



The cells which break away from the group, and so leave vacuities in its 

 conformation, resemble in their isolated condition the ceUs of Clilamydomonas. 

 Such detached cells were deemed by Ehrenberg equally capable of fission as 

 the persistent members of a colony ; Cohn, however, has never observed the 

 phenomenon, and believes, on the other hand, that, after swarming for a time, 

 they enter into a state of rest, and by shedding their locomotive filaments 

 assume the Protococcoid state. This ' still ' form of the Gonium-(ie\\.s, is in aU 

 likehhood also entered upon when the water in which they live is dried up 

 and the functions of life suspended ; and it may be that on the addition of 

 fresh water such cells give issue to motile forms, and thus a j^araUel series of 

 changes occiu' in tliis organism to that observed in Stephanosphcera. Xever- 

 theless a resting-stage of Gonium is not positively demonstrated ; for although 

 analogy is in favour of it, and the occurrence of Protococcoid cells in com- 

 pany mth the ordinary tabular groups suggests the probability that these 

 are ' still ' cells, yet the absence of characters to distinguish them from the 

 swarm-spores of other Algae renders their determination at best a matter of 

 doubt. 



Development by fission as described is, therefore, the only mode proved to 

 exist ; it resembles that in Chlamyclococcus and St(]}hansophcera , by which 

 macrogonidia are formed. The production of microgonidia, as seen in both 

 the genera just named, as well as in Eudorina {Pandorina) and Volvox, is as 

 yet unkno^vn in Gonium. 



Respecting its relation to other Volvocinece, it is to be observed that, 

 although there are striking differences, there are, on the other hand, decided 

 natui'al afilnities betwixt them and Gonium. Thus, although the envelope - 

 cell is so imperfectly developed that it cannot be represented as a special 

 shut sac, as in the case of Stejjhanosjjluera, Chlamydococcus, &c., yet it is 

 analogous to the envelope-cell of those genera in its relation to the cell-con- 

 tents ; and, besides, in the case of the intimately allied Eudorina eJegans, the 

 common envelope, which resembles that of SteijJianosplKxra, is found fii^st as 

 a simple, and later as a double fine cell- membrane. (In Pandorina, indeed. 

 Professor Henfrey asserts the mucous envelope to be devoid of a limiting 

 membrane.) 



Again, the primordial cells of Gonium are enclosed in a special membrane, 

 and not mere globules of protoplasm unprotected save by a pellicular layer of 

 the same substance ; thus the disposition in Gonium (the primordial cells 

 enclosed by a membrane, the envclope-ceU not invested) is just the reverse of 

 that in Chlami/dococcus, ChJamydomonas, and Steplianosjjlupra. However, the 

 existence of a membrane aroimd the primordial cells is not an anomalous cir- 

 cumstance among the Volvocinece, since, in certain stages of development, a 

 firm closely applied membrane is produced around the cells of the other 



