THE CTENOPHORES 3449 



In spite of the variety of forms to be found, the Coelenterata are almost as inca- 

 pable of higher development as the Echinoderms. Like the latter, they have failed 

 to make any way in fresh water, not to speak of the land. A few free-swimming 

 jellyfish, a minute attached polyp, and some degenerate sponges are, indeed, found 

 in fresh water, but these can hardly be looked upon as successes. While, at pres- 

 ent, it is not easy to connect the Coelenterata with any other group, inasmuch as 

 they appear to stand without any near relatives among the higher animals, they 

 have a special interest, since they are considered to represent a stage in the develop- 

 ment of animal life through which all the higher forms have passed. Some simple 

 form of Coelenterate may have given rise to all the higher animal forms, the 

 modern Coelenterates the sea anemones, corals, etc. being those descendants of 

 the primitive simple form which have retained the original type of organization 

 almost unchanged. 



THE CTENOPHORES Group CTENOPHORA 



f 



Although all are agreed that the so-called Ctenophores are members of this sub- 

 kingdom, their exact position is not clear. The Ctenophores are glassy, trans- 

 parent creatures, either shaped like apples, melons, or Phrygian caps, or else 

 forming bands, often a yard in length, and thickened at the middle. Several 

 types are shown in the colored plate. The marvelous transparency of all but one 

 (Beroe] is especially remarkable. They inhabit the open sea, or are driven by cur- 

 rents and winds near the coast and into harbors. Their position in the water is 

 usually more or less vertical, the mouth being turned downward. The organs from 

 which this group takes its name are the ribs, which either run from pole to pole, or 

 else only for certain distances along the meridians, which are often symmetrically 

 arranged. These ribs consist of rows of short transverse combs, each being 

 formed of a row of cilia. The cilia forming a comb are connected at their bases, 

 but are also capable of independent movement. As they wave to and fro, they con- 

 stitute what is called a swimming or rowing plate. The activity of these rows of 

 plates depends upon the will of the animal, which can move either the plates of a 

 single rib, or all the ribs together; this latter movement resulting in slow locomo- 

 tion in the direction of the apical pole, i. e. the pole turned away from the mouth. 

 The body is capable of various swift, light, and graceful movements, for in addition 

 to the rowing plates there are other structures, such as the oral umbrella and the 

 capturing filaments or tentacles, with their hair-like branches. These tentacles, 

 which are attached like arms at the sides, are capable of erection, or of Withdrawal 

 into pockets. There is great variety in the development of these accessory organs 

 of locomotion. For instance, the Cydippidce have only arms, which, with their 

 branches, serve for capturing food as well as for steering. In other orders, vertical, 

 oar-like, dermal folds stand out from the body, by means of which the movements 

 become more rapid and energetic. Seme species of Eucharis, by suddenly shutting 

 up the oral umbrella, can jerk themselves forward; and when successive jerks of 

 this sort cause the body to move with greater speed than usual, the arms are with- 



