Marvels of the Universe 



541 



THE BOMMI FISH. 



Apparently it is the other fishes that are the chief enemies of the Bommi, for its flesh is unpalatable, and it is therefore 



despised as food both by shore-bird and man. 



the fact that their polyp-cells are always seated upon only one side of the stem or branch. One of 

 the characteristics of this large and widely distributed family — a characteristic shared in a less 

 pronounced degree b\' some other families — is the production of special polyps in special cells 

 which possess neither tentacles nor mouth. They are set apart for the special duty of defending 

 the colony and of catching food. They are armed with stinging-thread cells, and these threads are 

 shot out on suitable occasions Hke the harpoon of the whaler. Other species have similar stinging- 

 threads coiled up in microscopic cells of their tentacles ; and some, instead of having threads with 

 barbed points, have clinging discs which adhere to their prey and enable the tentacles to haul it to 

 the polyp's mouth. 



Among larger forms of these Hydroids that are worth looking for are the Bottle-brush Coralline 

 and the Lobster-hom. In the former the branches are arranged all around the stem, and after 

 curving from their connection with the stem they take an upward direction, so that they bear a 

 very striking resemblance to the useful kitchen implement whose name has been bestowed upon the 

 species. In the Lobster-horn the stem is stouter and straight, and the short finer branches are 

 similarly arranged in a series of whorls, so that the likeness to the long feelers of a lobster is by 

 no means a fanciful one. 



In aU these Hydroids the stem with its cells, which are all composed of a thin, horny substance 

 of the same nature as the hard parts of insects, is invested with a continuous layer of thin jelly- 

 like flesh. When one of the polyps captures some microscopic creature and digests it in its interior 

 cavity he alone does not get the benefit of that food. Although there is no circulatory system of 

 blood-vessels, or any other perceptible method of transmission from one part of the colony to the 

 others, there is an imperceptible system. This consists in the minute lashes, or cilia, with which 

 the investing coat is covered. By the constant vibrations of these cilia the food digested by any 

 one polyp is distributed equally all over the colony. 



Sea-Firs and other Hydroids may be found by a little systematic searching on almost anything 

 that is submerged in the sea. They cover the stems of many of the seaweeds ; they stand up like 



