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 Medusae 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, 



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