62 
PHYSICS: E. DERSHEM 
frog the assumption of homozygosity of the female is inadequate if not ex- 
cluded. If we assume that the female is heterozygous for sex, and that it 
has the chromosome constitution 2A -\- x -\- y (where y maybe missing), the 
male must have the chromosome constitution 24 + 2 x. The haploid num- 
ber in the egg would be 5 12 '+ x, and the diploid number either 24 + 2 x or 
24 + x + y. The diploid number 24 + 2 x would give rise to a male, while 
a female might be produced by either the haploid number 12 + x or the dip- 
loid number 24 + x + y. It is, therefore, of some interest to find out whether 
or not the female has the haploid number 12 + x chromosomes. It is use- 
less to enter into further speculation until this point is decided, which the 
writer hopes may be possible in the near future. 
Summary. — The author has raised twenty leopard frogs produced by the 
methods of artificial parthenogenesis from unfertilized eggs to the age of 
from ten to eighteen months. Nine of these frogs are still alive. Some 
have reached the size of the full grown normal adult male. Both sexes are 
represented among the parthenogenetic frogs. Seven of the nine older frogs 
whose gonads were examined were males, and two were females. The 
parthenogenetic males possess the diploid number of chromosomes. 
1 Loeb, J., and Bancroft, F. W., /. Exp. Zool., Wistar Inst., Philadelphia, 14, 1913, (275); 
15, 1913, (379). 
2 Loeb, J., these Proceedings, 2, 1916, (313); The Organism as a Whole, New York, 
1916. 
3 Swingle, W. W., Biol. Bull., Wood's Hole, 33, 1917, (70). 
4 Brachet, A., Arch. Biol., Paris-Bruxelles, 26, 1911, (362). 
5 The other haploid number 12 + y may be left out of consideration for the present 
since it is possible that such eggs may not be able to develop. 
THE RESOLVING POWERS OF X-RA Y SPECTROMETERS AND THE 
TUNGSTEN X-RAY SPECTRUM 
By Elmer Dershem 
Department of Physics, University of Illinois 
Communicated by R. A. Millikan, February 11, 1918 
This work was undertaken at the University of Iowa with the purpose of 
determining the wave lengths and the number of lines in the X-ray spectrum 
of tungsten with greater precision than had heretofore been done. 
The method adopted was the well known photographic one in which the 
crystal is slowly rotated so that it will progressively pass through all the 
angular positions which are required for reflection of the incident X-rays as 
demanded by the formula rik = 2 d sin 6, in which n is the order of the spec- 
trum, X the wave length) d the grating constant, and 6 the glancing angle of 
reflection. 
