14, MARCUS M. HARTOG. 
(Epithemia, Amphora) two cells (so-called “ frustules ”’) 
approach as “ progametes,’’ and division takes place in each ; 
and their offspring conjugate two and two, in the young state 
consequent on recent fission. 
In the Conjugate Sirogonium the gametes are somewhat 
unequal, and are separated by septa from sterile cells; the 
male is formed from the vegetative cell by the marking off of 
two sterile cells, one on either side, the female by marking off 
of a single sterile cell. 
Facultative gametes occur in all divisions of this group, or 
rather a vegetative cell, instead of assuming the character of a 
gamete, assumes that of the zygote, constituting the azygo- 
spore of De Bary. 
In the genus Votvox a colony is formed by the segmenta- 
tion of a single reproductive cell; at an early stage of this 
process certain cells undergo no further division, though they 
continue to increase in size. These large cells may behave as— 
(1) Parthenogonidia, which after the maturity of the 
colony begin segmenting on their own account to reproduce a 
fresh colony ; (2) ‘‘ Oogonia,” which on their maturity, with- 
out further division, assume the character of oospheres; “S per- 
matogonia” which at maturity undergo rapid segment- 
ation and are resolved into the numerous spermatozoa, which 
are biflagellate like the colonial cells. Euporina, another Vol- 
vocine, is anisogamous, the megagametes being flagellate. 
All the cells of the sexual colonies are fertile, either all becom- 
ing spermatogonia and segmenting into spermatozoa, or all 
assuming directly the function of oospheres.! 
The Confervoid OrpoconiacE# are also oogamous. Here, 
on the bipartition of a vegetative cell, the one daughter-cell 
enlarges to form the oosphere, the other is sterile. We may 
perhaps regard the latter as a gamete arrested in its develop- 
ment. The apical protoplasm of the oosphere grows upwards at 
one side pushing the cell-wall into a short beak, soon perforated, 
or merely forms a hole at this point. The cytoplasm con- 
1 The case of Pandorina will be treated below, p. 72. 
