THE JELLYFISH AND THEIR ALLIES 



most animals of this sort, they do not attach themselves to seaweed or stones, but 

 live on fine sand, into which they sink the posterior end of the stem. Numerous 

 thread-like appendages of this buried part penetrate the sand in all directions, 

 thus firmly attaching the animal. The mouth at the anterior end is encircled by 

 tentacles, a second circle of tentacles surrounding the widened part of the body 

 which contains the stomach. Immediately above this latter circle, the buds stand 

 in clusters; in summer they are found in all stages of development, and even 

 while attached to their stalks assume the complete structure of a medusa. They 

 move their umbrellas actively, break loose, and thus complete the circle of develop- 

 ment or alternation of generations. Bougainvillea ramosa is another form in which, 

 owing to the stock being branched, the division of labor is even more clearly seen; 

 some of the individuals are feeding and some are reproductive, these latter turning 

 into swimming bells, and breaking loose. Both these forms are small, as indeed 

 are the great majority of the hydroid stocks, but whole forests of hydroid- 

 polyp stocks may be seen on the reefs in the Pelew islands, almost as tall as a 

 man, and with roots three or four inches in diameter. A bather, entering such a 

 forest, is terribly stung, the pain lasting for hours. A solitary form (Monocaulus 

 imperator} the upper portion of which is here figured nearly related to 

 Corymorpha, and found 

 in the Northern Pacific, 

 attains still larger pro- 

 portions. These ani- 

 mals, brought up during 

 the Challenger expedi- 

 tion from a great depth, 

 were more than two 

 yards in length, with 

 a proportionate diame- 

 ter. 



As examples of 

 stocks of which the re- 

 productive individuals 

 do not swim away as 

 jellyfish, we may select 

 the pretty, feathered, 

 plant - like creatures 

 found along the sea- 

 shore, which are often 

 thought to be plants 

 but are really animal colonies, well known types being Sertularia and Plumularia. 

 In these cases, in addition to the nutritive individuals, there are the egg-bearing 

 individuals which never turn into free-swimming medusse. In saying this, it must 

 be left undecided whether these colonies are degenerate, that is, were once capable 

 of producing medusse, but have now lost the power; or whether they are in a lower 

 stage of development, above \vhich they have never risen. One small form which is 



Monocaulus, UPPER THIRD (much reduced). 



