172 SEAWEEDS 
resembles Entoderma. Its thallus is densely branched, 
and the branches eventually grow together and form 
a continuous plate. Phacphila and Acrochete are 
small epiphytic forms on other Alge, allied to Bolbo- 
coleon, as also is Acroblaste, which grows on stones 
and shells. The latter has both creeping and erect 
filaments. 
The Reproductive Organs.—Conjugation of gametes 
is known in Ulothrix (as well as in Bumilleria, a 
fresh-water genus). The gametes are formed in the 
ordinary vegetative cells, and escape by a side open- 
ing. They are ovate in shape, have two cilia and a 
red spot. They conjugate in pairs, and occasionally 
in threes, and form a zygote. (The gametes have 
been observed to germinate without conjugation 
after coming to rest, but the filaments are more 
slender than those emitted by the zoospores.) The 
zygote increases in size and its membrane becomes 
thicker; after a period of rest its contents divide 
up into a number of zoospores which germinate 
after swarming. Pheophila has gametes with four 
cilia, which conjugate with their posterior ends. 
Ulothrix is reproduced non-sexually by zoospores, one 
to four in number, produced in the vegetative cells, 
as the gametes are. They are larger than these and 
have each four cilia. In Ulothrix implexa zoospores 
are sometimes formed which do not escape, but sur- 
round themselves with a membrane, and eventually 
germinate after the decay of the wall of the mother- 
cell. Chetophora also possesses zoospores with two 
cilia, and these sometimes fail to escape and behave 
like those of Ulothria implexa. Entoderma, which, like 
