BIOLOGY. 283 



1. To test the relative genetic values of color characters of larva and cocoon as exhibited in 



parental lots, as to their conformity with previous results. 



2. By interbreeding within these lots to secure pure strains with reference to certain 



characters. 



3. To test the effect of interbreeding as measured by fertility or other indicators. 



4. To discover the genetic or other physiologic relation of the many color-shades exhibited 



in hybrid crosses. 



5. To test the effect of various influences (interbreeding, and certain environmental con- 



ditions) on the product of the salivary glands, namely, the silk. 



As a result of Experiment 1, the genetic status of larval and cocoon-color 

 characters, as exhibited by the various races to be used in further experi- 

 mentation, was established by the work carried on in *1920 to 1922. 



Ninety broods of worms, running from 100 to 300 worms in a brood, were 

 under constant surveillance during the spring and summer of 1923. In 

 certain lots, material has been secured study of which will give data for com- 

 paring the effect of cross-breeding versus interbreeding in this material, and 

 eggs have been obtained for continuation of this series of work. 



In lots of silkworms reared under various conditions of temperature and 

 humidity, material has been secured to test the effect of these conditions on 

 the salivary glands and their secretion, namely, the silk. This material is, 

 however, limited as the conditions proved too strenuous for the worms and 

 many fatalities resulted. However, sufficient material was secured to 

 produce, when studied, tentative results, which will form the basis of next 

 year's work along this line. A serimeter has been secured for testing the 

 breaking strength of the silk fiber. 



The relations of color of blood in the silkworm to color of the cocoon, and 

 to the color of the egg and the "breaking" of cocoon-color in hybrids, are 

 being studied. 



Sufficient broods of eggs have been secured from the lots reared this year, 

 to serve for the continuance of the project in 1924. 



Morgan, T. H., A. H. Sturtevant, and C. B. Bridges, Columbia University, 

 New York. The constitution of the germ-material in relation to heredity. 

 (For previous reports see Year Books 15-21.) 



Since our last report about 40 new mutants have been added to our stock. 

 The most useful are the new dominants that are especially suited to experi- 

 ments involving crossing-over. Their use avoids the necessity of first making 

 up double recessive stocks. Among the new dominants may be mentioned: 



(1) A bristle mutant, called stubble, half a unit to left of spineless in chromo- 

 some III. 



(2) A beaded-in-X (called beadex), whose locus in the X-chromosome is to the right of 



bar and close to fused. 



(3) A crumpled wing (jammed) whose locus (at 39) is between dachs and black, in 



chromosome II. 



(4) A new minute (i) between hairy and dicha?te, in chromosome III, that will be useful 



in studying the large cross-over fluctuations in that region. 



(5) Another minute (j), three units to the left of rough in chromosome III. 



(6) A minute (m), about 30 units from lobe, in chromosome II. 



(7) Lobe-', an allelomorph of lobe, more extreme than lobe but less extreme than lobe-*. 



(8) A bristle mutant (off) in which a few bristles are absent from the abdomen, leaving 



the sockets as in hairless. 



The last mutant is not lethal when homozygous, as are so many other 

 dominants. In the pure form (homozygous) the eyes are rough, but not in the 



