1885. ] Zoology. 85 
dependent upon the powers of the human retina, they do not 
necessarily determine the same for the retina and visual nerves of 
the lower animals, Indeed, the presence of well-developed eyes 
in many of the animal forms inhabiting the greatest depths, no 
less than the varied coloring of their teguments, have frequently 
been taken in evidence to prove not only the existence of light 
there, but also the unequal visual powers of the different organ- 
isms. Professor Verrill has recently enunciated the startling prop- 
osition that not improbably light of the intensity of ordinary 
moonlight may penetrate to depths of 2000, or even 3000 
fathoms, and that possibly some sunlight penetrates even to the 
lowest bottom of the ocean. Evidently, however, the tegumen- 
tary coloring as we observe it has no bearing on the question at 
issue, inasmuch as it appears as such only when brought within 
the influence of white light, which may be at, or quite near to, 
the surface of the water. Whether or not the quantity of phos- 
phorescent light emitted by the organisms themselves is sufficient 
to account for the full development of visual organs, still remains 
to be proved. In the meantime, the recently conducted investi- 
gations of a special committee of Swiss scientists, among whose 
names we find those of Sarasin, Soret, Pictet, C. De Candolle, and 
Fol, seem to affirm in a general way the conclusions reached by 
Forel—namely, that luminous penetration extends to only mod- 
erate depths. Three candles (contained in a lantern), immersed 
in the clearest water of the Lake of Geneva, were visible at a 
depth of 30 meters; and an electric light, at 3 meters further. 
The distance of clear vision was found to be but very feebly de- 
pendent upon either the increase of brilliancy in the luminous 
body, or its absolute magnitude. The extreme limit of the sun’s 
luminous action was determined photographically to be 250 
meters, beyond which absolute darkness was supposed to prevail. 
—The Nation. 
ON THE STRUCTURE OF THE BRAIN OF ASELLUS AND THE EYE- 
LESS FORM CecipoT#A.—The results presented grew out of an 
attempt to compare the nervous system, particularly the brain 
and other cephalic ganglia, of the eyeless species of cave-inhabi- 
ting Crustacea and insects with the allied eyed forms. After de- 
1 Read at the Newport Meeting of the National Academy of Sciences, Oct. 4, 1884. 
