122 
ZOOLOGY: J. P. BAUMBERGER 
A large number of experiments were made with lenses, etc., submerged 
in mercury iodide solution, data for which there is no room here. The 
curious result appeared that if the solution refracts more strongly than 
the submerged glass, and the lens is well centered as to the beam of 
light, the ellipses remain strong and clear. Hence the refraction of 
the solution and of the glass need not be identical. The dispersion B 
is particularly well determinable. The refraction at X in this case will 
be subject to 
ii:' = m' - 1 + = M - 1 + 2^/X2 + AN/e 
when AiV is the displacement produced on submerging the lens of thick- 
ness e at its middle and primes refer to the solution. The following 
is an example of results. K' for the solution is found as a whole from 
the full and empty trough. 
Lens e K' AN fi 
cm. cm. 
1 diopter 0.138 0.6140 0.0078 1.5315 Ellipses strong 
2 diopters 0.200 0.6140 0.0107 1.5345 Ellipses strong 
5 diopters 0.248 0.6140 0.0187 1.5126 Ellipses faint 
10 diopters 0.447 0.6343 0.0205 1.5625 Ellipses vague 
The first two cases are good, the last two untrustworthy. To per- 
fect this method a solution must be found whose dispersion constants 
are not so enormous compared with glass as the mercury iodide solution. 
' Note from a Report to the Carnegie Inst, of Washington. 
2 Washington, Carnegie Inst., Fub., No. 249, 1916, chap, ix, cf. Amer. J . Set., New 
Haven, 40, 1915, ^299-308;. 
Mr. R. W. Cheshire, Phil. Mag., London, 32, 1916, (409-420), has recently used Topler's 
method for the same purpose with marked success. 
^Washington, Carnegie Inst., Pub., No. 229, 1915, § 40, 41, 42. 
THE FOOD OF DROSOPHILA MELANOGASTER MEIGEN 
By J. P. Baumberger 
BUSSEY INSTITUTION. HARVARD UNIVERSITY 
Communicated by W. M. Wheeler, December 26. 1 9 1 6 
In May, 1916, while rearing the banana fly on artificial media of 
fermented banana agar,^ I observed that visible fungus growths seldom 
occurred in the presence of many larvae. Such growths did appear, 
however, after pupation or if only a few larvae were present. Examina- 
tion showed the surface growths to be largely yeast cells. 
Further investigation showed that adult flies, pupae, larvae, and eggs 
