DEPARTMENT OF GENETICS. 



119 



It is probable, therefore, that explanations for departure from an 

 equality sex-ratio which are based on mechanical advantages of one or 

 the other type of sperm because of its size are not well founded. 



The effect of stateness of sperm on the sex-ratio. — Students of Amphibia 

 have laid stress upon staleness of gametes as a factor in the production 

 of an excess of males. It has been suggested that stale sperm might 

 affect the sex-ratio in man. To test this matter, Miss Jane Hubbard, 

 working under Dr. Little's direction, is using the northern squash 

 beetle, Epilachna borealis. In this species copulation occurs only 

 once, while such a female lays its eggs throughout the summer season. 

 At the end of the season the eggs laid must have been fertilized by 

 sperm that has been retained by the female for months. The work is 

 not finished. Table 5 gives the totals of observations made to the 

 date of report. 



Table .5. — Numbers of female beetle?. {Epilachna borealis) confined during 1921, number of 

 eggs laid, n umber of larvcB, of pupoe, and of imagines resulting from them. 



The work is being continued; it is too early to announce results. 

 The heavy mortality of the experimental lines is striking. 



Selection of Sex-Intergrades in Daphnia. 



Dr. A. M. Banta has, with the assistance of Mr. L. A. Brown, 

 continued changing the proportional degree of sex-intergradation in his 

 interesting biotype of Daphnia longispina (see Year Book 1920, p. 12). 

 He reports the main results of the year in this topic : 



''An effect of selection has been obtained wherever attempted with inter- 

 grades of Daphnia longispina. With strains I and III, originating from 

 sisters, the effect of selection appeared after six generations of selections, 

 during which the stock was reared under uniform conditions. The curves 

 for the two strains fluctuate considerably, but the divergence between them 

 is never eliminated. (Really the selection is only in the low strain. III, 

 since the high strains can not be maintained too high because of consequent 

 low productivity and ultimate sterility.) Return selection has also been 

 effective in every one of the 10 cases in which it has been carried out, though 

 it has not been effective with equal promptness or to an equal degree with 

 the different strains. Strains X and XXII are returns to high from low. 

 Strain XXII is less successful as a return selection than strain X, but it 

 materially diverged from strain XII, from which it was derived. We have 

 obtained through selection a divergence between two selected strains; a 



