154 GENERAL HISTORY OF THE rNFUSORIA. 



the water included in the cells is mthdra^Ti, whereupon their contents con- 

 tract themselves into a globular form, revealing the investing membrane in 

 its entii'e periphery. Again, when the mucous envelope breaks up by difflu- 

 ence, the cells show a tendency to separate : the link-Kke canals are first 

 drawn out, and subsequently give way at the point of junction of the two 

 processes which form them — and this mth such a degree of elasticity, that 

 the cells appear to burst from one another mth a spring ; and thus at length 

 the entire organism is resolved into an irregular collection of cells. 



In the immatm^e period (XIX. 33-36) the outhne of the cell-membrane is 

 spherical ; for the angular figure and the development of the jimction-pro- 

 cesses are subsequent phenomena. Further, the extension of the processes 

 at times goes on so far that the Gonhmi-ceRs at fii'st sight appear detached 

 from each other and free, which is never the case natui^ally. 



In other points of organization the cells of Gonium correspond with other 

 loricated swarm-cells, particularly with those of Chlami/domonas. Their con- 

 tents consist of protoplasm coloured by chlorophyll, among which, in older 

 specimens, are numerous corpuscles (the ova of Ehrenberg) that impart a 

 deeper coloiu^ing ; of a central circumscribed darker corpuscle, which, as par- 

 ticipating in every act of fission of the cell, must be esteemed a nucleus ; of 

 several vacuoles, often numerous but occasionally wanting, and of two or 

 three sharply- defined vesicular spaces, constant in position at the base of the 

 filaments (XIX. 33). The last-named are the locomotive organs of the 

 organism, are two in number, and proceed from the protoplasm, passing 

 through foramina in the special celL-wall, and afterwards through the com- 

 mon mucilaginous envelope, so as to appear, in the polar aspect, like out- 

 stretched fibres from the tabular organism. 



The movements of Gonium resemble in all respects those of Steplianosphcera 

 and Chlcwiydococcus and other swarm-cells. The plant revolves on its short 

 axis, so that in its polar aspect it appears like a rotating surface, whilst in its 

 equatorial it has on the contrary a linear outhne. 



In the coui'se of its development by self- division, neither the general mu- 

 cilaginous coat nor the cell-membrane is concerned, but only the contents. 

 The fission into 16 segments to form a new colony has not that simultaneous 

 character which Ehrenberg implies, but takes place by four stages or genera- 

 tions, in every one of which a bisection of each ceU already developed ensues 

 (XIX. 35). It is only in fully developed Goni wn-tahlets that self-division 

 is effected — for example, in such as have cells ^-J-u'" i^^ diameter, and sepa- 

 rated from one another by the elongated intercommunicating processes, and 

 w^here those cells have the disposition described as characteristic. 



On the completion of the act of self-division by the construction of 16 

 small cells, these are found occuppng just the same relative position within 

 the membrane of their parent-cell as do the members of a perfect Gonium 

 (XIX. 36). Amid numerous examples of the plant, specimens may be met 

 with abnormal in the number of constituent cells ; for instance, colonies of 

 only 8 cells occur, which are exphcable on the supposition that the last 

 stage of fission, i. e. the last act of generation, has been arrested, and only 

 three such acts completed. The like irregularities are often noticed in other 

 Volvocinece. 



The primordial cells of the newly generated colonies appear unconnected 

 with each other, whilst the mother- cell wall, which still includes them, is 

 considerably distended and elongated in one direction (XIX. 30). The move- 

 ment of the colony as a whole continues until the last stage of fission is com- 

 pleted, whereupon it ceases, and the newly formed groups commence a move- 

 ment within their enclosing cell, sometimes presenting themselves in one 



