If we examine them with a lens we find that there are little cup-like bodies projecting from each portion or branch of the stem-like structure, and that the stem itself is hollow, with a communicating pore at the base of each cup. This constitutes the skeleton only of the colony—the dead matter, so to speak, which persists after the living creatures have perished; but if the specimens collected have been obtained fresh from the sea, placed in a glass of sea water, and then examined with the aid of a lens, little jelly-like hydroids or polypites will be seen to protrude from the cups, and extend their short arms in search of food.
Fig. 81.—The Herring-bone Polype (Halecium halecinum)
Each of the little creatures has a tubular stalk which passes through the hole at the base of the cup, and is continuous with a tube of gelatinous material in the interior of the horny stem, and thus each member of the colony is directly connected with all the others, so that any nutrient matter collected and digested by one member may be absorbed into the central tube for the nourishment of the entire company of little socialists, the activity of the one being thus made to compensate for the laziness or incompetency of others. And this provision seems to be absolutely necessary for the well-being of the colony as a whole, for a close examination will often show that a kind of division of labour has been established, since it includes two or three distinct kinds of polypites, each adapted for the performance of a certain function. Thus, in addition to the feeding or nutritive members of the community, there are some mouthless individuals whose sole function seems to be the production of eggs for the propagation of the species, while others, also mouthless, develop an enormous number of stinging cells, probably for the protection of the whole community against its enemies, and these must therefore be provided, as we have seen they are, with a means by which they may derive nourishment through the agency of the feeding polypites.
Fig. 82.—Tubularia indivisa
