ALTERNATE GENERATIONS. 257 
little individual, settling upon some shell or 
stone, or on the rocks in a tide-pool, where it 
will sometimes cover a space of several square 
feet. Rosy in color, very soft and delicate in 
texture, such a growth of Hydractinia spreads 
a velvet-like carpet over the rocks on which it 
occurs. They may be kept in aquariums with 
perfect success, and for that purpose it is better 
to gather them on single shells or stones, so 
that the whole community may be removed un- 
broken. These colonies of Hydractinia have one 
very singular character: they exist in distinct 
communities, some of which give birth only to 
male, others to female individuals. The func- 
tions, also, are divided,— certain members of 
the community being appointed to special offices, 
in which the others do not share. Some bear 
the Medusze buds, which in due time become 
laden with eggs, but, as I have said, wither and 
die after the eggs are hatched. Others put forth 
Hydroid buds only, while others again are wholly 
sterile. About the outskirts of the community 
are more simple individuals, whose whole body 
seems to be hardly more than a double-walled 
tube,-terminating in a knob of lasso-cells. They 
are like long tentacles placed where they can 
most easily seize the prey that happens to ap- 
proach the little colony. The entire community 
is connected at its base by a horny net-work, 
Q 
