832 



SCIENCE 



[N. S. Vol. XXXIX. No. 1014 



by Professor Theodore W. Eichards, of Har- 

 vard TJniversity, and Mr. Max E. Lembert, 

 who came to America from the Grand Ducal 

 Technical School of Karlsruhe for this pur- 

 pose, on the initiative of Professor Bredig and 

 Dr. Pajans. The latter well-known investi- 

 gator, as well as Sir William Eamsay, Pro- 

 fessor Boltwood, Miss Gleditsch and Mr. 

 Miner generously provided the experimenters 

 with residues containing lead of this sort. It 

 was found that all the lead obtained from 

 uraninite, carnotite or thorianite exhibited a 

 lower atomic weight than ordinary lead, the 

 deficiency amounting in one case to as much 

 as 0.Y5 unit. The ultra-violet spectrum of a 

 typical specimen appeared to be exactly iden- 

 tical with that of ordinary lead. The neces- 

 sary inference seems to be that lead from 

 radioactive sources consists of a mixture of at 

 least two substances, of which one is ordinary 

 lead. The foreign substance must be very 

 similar to ordinary lead and very difficult if 

 not impossible to eliminate by chemical means ; 

 for many precautions were taken to purify the 

 samples. This amazing outcome is contrary to 

 Harvard experience with several other ele- 

 ments, notably copper, silver, iron, sodium and 

 chlorine, each of which has been found to have 

 a constant atomic weight, no matter what the 

 source may have been. The new results on 

 radioactive lead are qualitatively in accord 

 with a recent hypothesis brought forward 

 independently by Fajans, by Eussell, and by 

 Soddy, although quantitatively not exactly 

 consistent with it. A preliminary paper, set- 

 ting forth the detailed methods and results, 

 was sent to press on May 14, and will appear 

 in the July number of the Journal of the 

 American Chemical Society. The research 

 was generously subsidized by the Carnegie 

 Institution of "Washington. 



SPECIAL ABTICLES 

 THE PRODUCTION OF MALES AND FEMALES CON- 

 TROLLED BY FOOD CONDITIONS IN 

 HYDATENA SENTA 



The factors that regulate the production 

 of the sexes in the rotifer Hydatina senta 



have been zealously sought for during the 

 past twenty-five years and various results 

 have been obtained. Temperature, starva- 

 tion of the young females, unknown external 

 agents, and finally the intangible unknown 

 internal factors, have been decided to be the 

 potent influences that regulate the sex ratio 

 in the parthenogenetic reproduction. 



Mitchell'- has recently experimented with 

 the rotifer Asplanchna and has found that a 

 sudden change of the food will bring about 

 the production of a certain one of the poly- 

 morphic forms of this rotifer. This partic- 

 ular form of the female produces males. He 

 therefore concludes that a change of food 

 eventually causes male individuals to be pro- 

 duced. He suggests that this food factor may 

 be found to regulate the sex production in 

 Hydatina senta. 



Some time ago it was shown by Whitney'' 

 that uniform food conditions caused a pro- 

 duction of only females for 289 generations in 

 Hydatina senta. Since that time many at- 

 tempts have been made to find some food con- 

 ditions that would cause the females to pro- 

 duce only male offspring. Many kinds of 

 mixed cultures of various protozoa have been 

 tried as food and a varied assortment of re- 

 sults have been obtained. This winter pure 

 cultures of several species of protozoa have 

 been grown and more definite results have 

 been obtained. Several kinds of colorless 

 flagellates as well as several kinds of green 

 flagellates were reared and used as food for 

 Hydatina senta. Some were tried as a con- 

 tinuous diet and others were used in an inter- 

 rupted diet. The colorless flagellate, Polytoma, 

 was found to be the most satisfactory as a 

 continuous diet for producing only female 

 offspring. A species of the green flagellate 

 Dunaliella (Teoior) or Ohlamydomonas (Gohn) 

 was found to be the most effective in causing 

 the females to produce a high percentage of 

 male offspring by an interrupted diet. 



Some fertilized eggs were taken in Novem- 

 ber from a covered culture jar of rotifers that 



1 Jour. Exper. Zool., Vol. 15, August, 1913. 



2 Biol. Bull, Vol. 22, 1912. 



