G08 
by niglit, would probably be injured by exposure to tlie full rays 
of the sun. Chun has shown that the Ctenophora of the Bay 
of Naples execute periodic movements of a similar kind ; and 
the Naturalists of the “Challenger” expedition found that tracts of 
sea, which during the day appeared perfectly barren, would at 
night teem with organic life of all kinds. Many pelagic forms, 
like those inhabiting great depths, are furnished with abnormally 
large eyes, suited to their nocturnal habits. The surface of the 
sea is at night, as is well known, often brilliantly illuminated 
by the phosphorescence of such animals as Noctiluca, which may 
occur along the English coast in numbers prodigious enough to 
cause a glass of water taken from the sea to appear quite milky ; or 
as Phyllosoma, Ascidians which form colonies some inches in length, 
and occasionally cover the surface of the water, on a quiet night, 
for miles. 
Among pelagic animals, a Worm, Alciope, has extraordinarily 
large eyes, which fill up most of its head. The eyes of the 
Cephalopods, or Cuttlefish, are among the most perfect organs of 
the kind met with among invertebrates, resembling in tlieir general 
features the typical vertebrate eye, without, however, having any 
true homology with it in detail. The IIyperina3, a sub-order of 
the Amphipod Crustaceans, possess eyes of an enormous size, as 
do the larva} of many of the higher Crustaceans, such as the Glass- 
crab (Phyllosomata). 
With regard to ento-parasites, it is almost universally the case 
that such forms arc blind. 
To recapitulate : it is difficult to account for the existence of 
animals with well- developed eyes inhabiting caves which no ray 
of light enters, except by supposing they are recent immigrants, 
or that disuse does not affect some forms so quickly as others ; 
wliile, as to similarly endowed deep-sea and pelagic species, it would 
seem that the presence of phosphorescent animals must be of great 
advantage to them. The existence of phosphorescence itself cannot 
be satisfactorily accounted for j but its presence in so many widely 
different forms shows that it must have a meaning, and it can 
hardly fail in some way to bo of use to its possessors. Blind 
animals in caves, as well as in the deep sea, are usually provided 
with specially acute organs of hearing or touch, the latter in the 
form of long anteiinm or other appendages, as in the Crustacea; or of 
