OF THE PHYTOZOA. 153 



like colonies sometimes moved horizontally, at others vertically, or rolled on 

 their edges like wheels by the aid of the pair of vibratile filaments of each 

 member projecting fi-om the siuface. 



The animal organization here represented is now-a-days generally ignored, 

 and Goaium takes up its position among plants. Prof. Cohn (to whom we 

 are so much indebted for oiu' knowledge both of Protozoa and Protophyta) 

 has contributed a valuable paper (Entw. d. mihr. Algen u. PUze) on this in- 

 teresting being, of which we shall present an abstract. 



The entii'e organism is invested by a colourless transparent muco-gela- 

 tinous envelope without any cellulose limit-membrane, whence it is that this 

 common envelope has frequently passed imobsen'ed unless some colouiing 

 matter, such as Indian ink, has been added to the water. 



The figiu'e varies according as the plant is viewed from above (on its 

 polar aspect) or from its side (on its equatorial aspect), being in the former 

 point of view a quadiilateral tablet with tnmcated angles and rounded cor- 

 nel's (XIX. 32), and in the latter a flattened spheroid. 



The simple or primordial cells (XIX. 33) enclosed in this mucous sheath 

 are sixteen in number, disposed in a imiform manner, so that fom- cells, 

 leaving a square interval in the centre, are bounded externally by twelve 

 others, three of which form one of the four sides of the organism (XIX. 32). 

 The central ceU of the three is, moreover, not in a line with the other two 

 on the same side, but set nearer to the centre ; hence each side of the tablet 

 is hollowed out in the middle. Closer research also shows that each of the 

 cells is not spherical, but polygonal, the four internal being six-sided (hex- 

 agonal), the twelve peripheral five-sided (pentagonal) ; the consequence is, 

 angular intercellular spaces are left, the central of aU being quacbangular, 

 and all the rest triangular. This arrangement of the primordial cells is 

 normally so regular, that Cohn represents it by a geometrical chagram ; still, 

 in aU tablets of Gonium this is not the case, and particularly in very young 

 specimens. 



The regular polygonal contoiu^ of the cells indicates that they are not 

 mere masses of soft variable protoplasm, hke those of Stephanospli<xra, but, 

 on the contrary', are each of them siUTOimded by a colourless, hyaline, deli- 

 cate but firm membrane, imposing on them theii' fixed form (XIX. 34). 

 This stiTicture indeed is not generally discernible, unless by some abnormal 

 conditions, or by the occiuTence of self-di^dsion (XIX. 35), in which, as 

 only the green contents are concerned, it comes to stand apart from the latter 

 as a distinct, separable sac. It can, moreover, be demonstrated by cnishing 

 the cells, when the chlorophyll escapes thi^ough the rent, and leaves the 

 colourless and fractiu-ed case. Cohn is con\inced that this membrane is 

 composed of cellulose, although, from the inability to isolate them, he has 

 been unable to prove it by chemical reagents. 



Without any preparation this investing membrane can, further, be detected 

 at the angles of the cells, fi'om each of which it is prolonged in the form of a 

 short tubular process, emptj' and colourless, the contents being restricted to 

 the general cavity of the ceU (XIX. 34). Each cell sends out such a jDro- 

 cess from its several angles to miite T^ith a similar one fi^om each contiguous 

 cell : in this way are formed the intercurrent cords or canals alluded to by 

 Ehrenberg. It follows also from this structure that the link connecting the 

 angles of conjoined cells, belongs one half to one and the other to its com- 

 panion-cell. 



The nature of the Gonhun-QdW^ and their connecting tubes is clearly dis- 

 played by observing the changes consequent on the gradual evaporation of 

 the water about them. For instance, on adding salt by degrees, a portion of 



