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. 
уу а 
Fig. 82. — Leptocephalus. 4. 
The range of vision of а Plagusia, а 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 zoeæ and other embryo crustaceans, and those 
of the adult; nor is the difference less between the size of the 
organs of seuse in embryo acalephs, echinoderms, mollusks, 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 delicate 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 
on 
morning, or late in the afternoon, or during the night; they 
5? 
