Ctenophora. ■7 j 



there to be seen. A very natural supposition — but still an error! 

 The aquatic animals see no colours ; most probably they observe no 

 more of them than a colour-blind person — that is to say the 

 difference of brightness alone. And further, water animals are 

 much less capable of observing differences of form than are their 

 relations on land. The fishes even, with their highly organized 

 eyes, can see clearly at close quarters only, and thus in a very 

 narrow field. Their eyes, too, when at rest are focused for near 

 objects (not as in land animals, for distant ones), and they "ac- 

 comodate" by approaching the lens to the cornea (not as in birds 

 and mammals by a change in shape). The reason for the deficient 

 development of the sense of sight in aquatic animals is a physical 

 one, namely the relatively slight transparency of the water. 



Ctenophora. 



Like Siphonophora and Medusae and many other inhabitants 

 of the high seas, such as some Molluscs, Annelids, Crustaceans 

 and even fishes, the Ctenophora have transparent bodies. The 

 reason for the possession of this "vanishing-cap" must be sought 

 for in the advantage which they gain by such a character. Prob- 

 ably the advantage consists in the difficulty which their enemies 

 have in seeing them, and in the facility with which they can sur- 

 prise and capture their prey. These transparent animals, even 

 the delicate Ctenophora and Siphonophora, are often voracious 

 robbers, frequently swallowing animals which one would suppose 

 might easily overcome them. Inside the cavity of Beroe or in the 

 pendant stalk of a Meduse are often seen small fish which the ap- 

 parently delicate organism dissolves and digests. 



In the Bay of Naples the following Ctenophora occur: the 

 barrel-shaped, comparatively tough Beroe (fig. 85); the much more 

 delicate Callianira (fig. Sy), Eucharis (fig. 86) consisting chiefly 

 of water; and lastly the curious Venus' Girdle, Cestus Veneris 

 (fig. 88). All of these attract the attention of the observer by 

 the beads of light which seem to run over the body in various 

 directions, displaying all the colours of the rainbow. This curious 

 play of colours is caused by innumerable little plates, which are 

 placed in vertical rows one above the other, and are moved up 

 and down with great rapidity. By them the rays of light are 

 reflected in such a way that the colours of the rainbow, which make 

 up white light, appear separately. These plates, arranged in rows 

 like the teeth of a comb, have caused these organisms to be called 

 Ctenophora ("comb-bearers"). 



