VOLVOCINES. 69 
from other zoospores. At their colourless apex they exhibit, like 
other zoospores, a red body placed on one side of the apex, and two 
long vibrating cilia, by which they move in the manner common to 
zoospores. The individual zoospores exhibit no marked differences, 
except that they vary in size within tolerably wide limits, but not ina 
manner to indicate the existence of two different sorts. 
Amongst the groups of isolated zoospores of different sizes some are 
at last seen to approach one another in pairs. They come into 
contact at their anterior hyaline apex, coalesce with one another, and 
assume a shape resembling a figure of 8. The constriction which 
marks their original separation disappears by degrees; and the paired 
zoospores form at last a single large green globe, showing at the cir- 
cumference no trace of their original separation. It may be seen, 
however, that the globe is larger than the individual neighbouring zoo- 
spores, that it has a strikingly enlarged colourless mouth spot, with 
two red bodies on the right and left, and that it is furnished with four 
vibrating cilia originating in pairs near the two red spots. The four 
cilia, however, soon become motionless, and together with the red spots 
disappear. 
This act of conjugation occupies some minutes from the first contact 
of the zoospores to the formation of the green globe. The latter 
becomes the oospore, which, after growing slightly larger, and assuming 
a red colour, germinates after a long period of rest, and brings forth a 
new Pandorina. There is hardly any appreciable difference, except in 
size, between the male and female zoospores. Most frequently a small 
zoospore pairs with a larger one; but two of equal size often unite. 
Probably both the females and the males vary much in size, the former 
more so than the latter, 
With regard to the entire plants from which the zoospores are pro- 
duced, there is little doubt that those of the largest size are females; 
but the sex of the smaller and middle-sized ones cannot be determined 
with any certainty. The germination of the oospore is like that of other 
Volwocinee, especially resembling in its early stage the germination of 
the resting spores produced by the microgonidia of Hydrodictyon utri- 
culatum. The oospore bursts, and produces a single large zoospore (in 
rare cases two or even three), which divides into sixteen cells, and 
becomes a young Pandorina. 
Plate XXVII, fig.2. Pandorina morwm—a, a very small family; 8, 
c, sixteen-celled families; d, eight-celled family ; e, solitary cell; /, the 
same, further magnified, showing process of subdivision; g, 32-celled 
family; h, small family undergoing division; 7%, 16-celled family 
divided into sixteen daughter families. All after Stein X about 500. 
Gunus 42. GONIUM. Miller. (1873.) 
Coenobium quadrangular, tabular, angles rounded, formed 
from a single flat stratum of cells, girt by a broad hyaline 
plano-convex tegument. Cells 16 (central 4, peripherical 12), 
polygonal, bright green, becoming with age disordered, granu- 
lose, connected by the produced angles, chlorophyllose vesicle 
central, furnished with colourless contractile vacuoles, and two 
long exserted cilia. 
Propagation by repeated division of the cytioplasm. 
L 
