114 CARNEGIE INSTITUTION OF WASHINGTON. 



2 are the same as the 2 permitting the growth of the dbrB tumor. The dbrA 

 tumor will continue to grow, however, only when a third factor called C 8t is 

 also present. Thus, Dr. Strong has shown that the physiological differences 

 between histologically identical tumors are genetic differences. 



The work has now reached a point where it will be necessary to conduct a 

 series of individual tests leading to the isolation of lines differing in single 

 mendelizing factors for susceptibility and immunity. 



Doctor Strong is continuing his work on these tumors with special reference 

 to their rate of growth and their relation to other spontaneous tumors which 

 have arisen in his stocks, while the experiments dealing with isolation of 

 single-factor lines Doctor Little hopes to carry on at the University of Maine. 



Cooperative Breeding of Mice. 



The need of a central agency to maintain mutant strains of mice has been 

 felt for some time. The preservation of such strains is a prerequisite to 

 extensive linkage studies. Inasmuch as this Department has come to be the 

 gathering-place of many mouse geneticists during the summer, it has been 

 requested to perform this service. In view of its limited resources and in 

 view of the danger from epidemics, the Department can not guarantee to 

 take care of all mutant strains that may be offered in the future, but it is glad 

 to be of such service as it can in this matter. 



At present the following stocks are on hand: 



(1) Lathrop Japanese waltzers, which will be bred by brother-to-sister matings. 



(2) Inbred dilute browns of Little. 



(3) Abnormal and control X-ray lines, including the gene for abnormal eye of line 85 



from Little. 



(4) Bagg albinos. 



(5) Storrs albinos, carrying the pink-eye factor; two wild lines. 



(6) Storrs-Little, a race parallel to the dilute browns, in which homozygotes of the 



different dilute and pink-eye combinations will be sorted out to provide 

 known stocks for testing the genetic constitution of the very confusing pale 

 combinations. 



(7) Piebald and black-eyed whites from the inbred race of Strong. 



(8) Dilute pink-eyed browns, which, with the introduction of the waltzing character, 



will become very nearly the ultimate recessive for the more familiar genes, 

 and hence be very valuable for the analysis of individuals of unknown 

 constitution. 



GERMINAL AND SOMATIC VARIATIONS. 

 Mutations in Cladocera. 



Cladocera are prevailingly parthenogenetic; hence all individuals of a 

 clone are expected to be alike except as mutations occur. . The species bred 

 by us are 13 in number and comprise 71 lines, as follows: Daphnia longispina, 



3 lines; D. pulex, 17 lines; Simocephalus vetulus, 5 lines; S. exspi?iosus, 10 

 lines; S. serrulatus, 21 lines; Simocephalus sp?, 2 lines; Ceriodaphnia rigandi, 

 1 line; C. megalops, 1 line; C. quadrangula, 1 line; Moina rectirostris, 2 lines; 

 M. a 'ffinis, 2 lines; M . macrocopa, 4 lines; Lathonuraf 2 lines. 



In addition to these 13 clearly distinct species, there are five morphologically 

 different types of Daphnia pulex and four different types of Simocephalus ser- 

 rulatus. These types have constant differences and some of them are doubt- 

 less entitled to specific rank. The usefulness of this varied stock as observa- 



