THE PELAGIC FAUNA AND FLORA. 177 



are also sometimes brilliantly phosphorescent. The lateral or- 

 gans, though they are prominent in the young, disappear or be- 

 come atrophied in the adult. We can indeed say, with truth, 

 that many of the young fishes, soon after they escape from 

 the egg, are only bundles of nerves, ready to be acted upon by 

 every influence of light, heat, or motion. 



Pig. 82. — Leptocephalus. |. 



The range of vision of a Plagusia, a thin, transparent pelagic 

 flounder, or of Leptocephalus (Fig. 82), a long, narrow, trans- 

 parent tape-like fish, is very great. In the case of the former, 

 it is really comical to see either eye winking at you through the 

 transparent head. The same disproportion exists between the 

 gigantic eyes of zoese and other embryo crustaceans, and those 

 of the adult ; nor is the difference less between the size of the 

 organs of sense in embryo acalephs, echinoderms, moUusks, or 

 annelids, and that of the same organs in the adult. 



The pelagic animals do not come to the surface at all times. 

 The day fauna is seen at its best only when the sea is smooth 

 and the sun bright. The least ripple on the surface, or the 

 retreat of the sun, is enough to send the more deHcate animals 

 into deeper water, beyond the reach of such disturbances. At 

 night again, calm, smooth weather is essential to the many noc- 

 turnal animals which come to the surface only in the hours of 

 darkness and disappear with the dawn. It is true, that occa- 

 sionally a tempestuous night brings out the phosphorescence, 

 but this is rare. 



Many of the pelagic animals undoubtedly sink during the 

 day some distance below the surface, in order to escape the 

 intense sunlight. The young of some discophores come to 

 the surface only early in the morning, soon after sunrise. 



Some acalephs, like Tima, Zygodactyla, and Staurophora, are 

 very abundant before ten in the morning, while the Polyclonia, 

 (Fig. 83), both old and young, swim about either early in the 

 morning, or late in the afternoon, or during the night ; they 



