1891.] Zoology. 577 
organic compounds that show allotropic forms.——The parts of Dr. 
Hintze’s'® Mineralogy continue to appear with commendable rapidity. 
The fourth part concludes the discussion of prehnite, takes up in 
order axinite, harstigite, and the pyrosmalite group, and begins the 
treatment of the micas, which occupies one-hundred-and-twenty-five 
pages, and is not yet finished. Although there are perhaps some 
omissions to be noted with respect to American occurrences, the 
thoroughness of the author’s work cannot be gainsaid. The analyses 
of biotite given in the article on that mineral number 177, and those 
of muscovite 120, in addition to some twenty or thirty of varieties of 
these minerals. Dufet 17 describes a new method for the determina- 
tion of the optical orientation and of the dispersion of the axes in 
triclinic minerals, and applies his method to the study of potassium 
bichromate. Mr. Lane ® illustrates a method for determining the 
' planes in crystals in thin section. -It is based in the relations existing 
between the zone-circles and face-points in a stereographic projection, 
ZOOLOGY. 
The Coloration of the Flounders.—Whoever has seen the 
flounders alive, or even dead but not deprived of their skin, has noticed 
the remarkable difference existing between the dorsal aspect exposed 
to the water and the ventral surface which in the living animal moves 
along the bottom. While the dorsal face is more or less pigmente® 
the ventral is white. Why is this? The school of Weismann, more 
Darwinian than Darwin himself, is accustomed to attribute the fact to 
hatural-selection ; and the school, which is rapidly increasing, ar- 
ing to which the environment affects the animal, ought to attribute * 
to a physical influence, in view of the fact that the ventral side receives 
naturally much less light than the dorsal. In truth, one cannot rae 
how natural selection could produce it. From this pean: of m oF 
coloration of the ventral side seems of no importance, and if it Is e 
one would think that it is more advantageous to the flounder = 
this side gray, like the dorsal, rather than white,—that is to say, -T 
Professor Cunningham, of the Marine Biological ESERE: 
recently studied this phenomenon, and believes that 1t 1s cued DY 
1 Handbuch der Mineralogie. 4te Lief., pp. 481-640. Leipzig, 1897. 
. Bull. Soc. Franc. d. Min., 1890, p- 341- 
18 Bull, Geol. Soc. Amer., Vol. II., 1891, P- 365- 
