104 LIVERPOOL BIOLOGICAL SOCIETY. 
a pigment-spot and pulsating vacuole, indistinguishable 
from one another except in size, the former being much 
smaller than the latter. The gametes moreover have 
always two flagels, the zoospores not unfzequently four. 
They may be produced on the same or on different indi- 
viduals. In the gametes there is to all appearance 
absolutely no external differentiation between male and 
female elements, though a rudimentary physiological 
differentiation is undoubtedly occasionally observable in 
the fact that swarm-cells produced in the same parent-cell 
will not conjugate. The ordinary course of reproduction 
is varied in some genera by departures which are exceed- 
ingly instructive. 
In the Ulotrichacee there is a gradual transition 
between zoospores and zoogametes, the only constant 
difference between the two organs being that the former 
have four, while the latter have only two flagels. ‘Those 
zoogametes which do not conjugate may germinate 
directly, but then give rise to smaller plants than 
those which spring from the zoospores. ‘he two kinds of 
swarmspore are never produced in the same cell, but in 
different cells of the same individual. The same is the 
case also with the Trentepohliaceze or Chroolepides. In 
Vaucheria (Siphonez) the zoospores, which are of consider- 
able size, instead of being biflagellate, are completely 
surrounded by a fringe of delicate flagels. In Botrydium 
(Botrydiaceee), on the other hand, the zoospores are uni- 
flagellate. In Dasycladus (Dasycladacez) the biflagellate 
zoospores conjugate only if produced from different 
individuals. In Hydrodictyon utriculatum, the water-net, 
(Hydrodictyez) from 30,000 to 40,000 minute biflagellate 
zZ ogametes are produced in the same cell or gametange ; 
and in this case swarm-cells from the same gametange 
undoubtedly conjugate, conjugation having been observed 
a 
