40 COCCOPUYCER. 
imperfect birth of the germ cells just described is repeated at the tran- 
sition to the third, and mostly even to the fourth generation, so that 
little arborescent groups are produced with twice or thrice-repeated um- 
bellate ramification, till at length the cells which form the outermost 
umbellules scatter out their germ cells, which, after a short swarming, 
fix themselves again to be developed into ramified stocks of new 
families "—Braun Rejuvenescence, p. 187. 
Plate XV. a, b, young cells; c, commencement of the first generation 
of daughter-cells; @, further progress of the first generation of progeny; 
e, second generation being evolved from the first; f, old plant evolving a 
third generation X 300, after Braun; g, zoogonidia. 
Sub-Family 7. PspiastRez. 
Ceenobium discoid, plane. 
For other features of this sub-family see the characters of the genus, 
which is the only one at present comprised within it. 
Genus 29. Pediastrum. Meyen. (1829.) 
Ccenobium plane, frond-like, discoid, or stellate, free swim- 
ming, formed of cells in a single, rarely in the centre in a 
double stratum, continuous, or with the cells here and there 
interrupted, perforate or clathrate. Cells polygonal, central 
entire or slightly emarginate, those of the periphery entire or 
two-lobed, the lobes wedge-shaped, either simple or two-toothed, 
sometimes elongated into a horn. _Cell-contents green, homo- 
geneous at first, then granular—Rabh. Alg. Eur. iii. 69. 
Formerly this genus was included in Desmidiacex, but the knowledge 
of its life history has shown that it has no relationship with the Con- 
jugate. Braun illustrated the development of one species (Rejuvene- 
scence, Pl. III.), and we have reproduced some of his figures (on Pl. XVI.) 
Fig. 1 is an old disc, in great part emptied by the birth of gonidia. 
Several of the empty cells exhibit a cross slit, through which the con- 
tents have been discharged. The order in which this emptying took 
place is indicated by the letters a, b,c, d,e. One cell is in the act of 
discharging the gonidia, these having in part entered the projecting por- 
tion of the hernia-like vesicle, formed by the swollen innermost layer of 
the membrane of the mother-cell, in part still remaining in the internal 
cell cavity. Three other cells still possess their perfect contents in 
different conditions. Two of them are filled by sixteen extremely closely 
crowded gonidia, only half of which are visible, as they form a double 
layer. The third unemptied cell is in the actual transition to the forma- 
tion of gonidia. It exhibits the first division of the contents into two 
halves, one of which already appears halved again. Fig. 2 is anew-born 
family immediately after the birth. The innermost layer of the mother- 
cell has wholly emerged from the old cell, as an extremely thin vesicle, 
enclosing the gonidia, the gonidia in the interior moving actively. Fig. 
8 is the same family, as seen from the upper surface. Fig. 4 is the same 
family, a quarter of an hour after birth. The gonidia, now at rest, have 
arranged themselves in a plane disc. Fig. 5 is the surface of the same 
family at the same stage. Fig. 6 the same family one hour after birth. 
The emargination of the cells has proceeded further. Fig. 7 the same 
again, but four hours after the gonidia ceased to move. The emargination 
of the border-cells has passed into the formation of horns, The cellsare 
