DEPARTMENT OF GENETICS. 105 



Selection with Sex-Intergrades of Simocephalus exspinosus. 



An effect of ''selection" in modifying the sex-intergrade stock of Simo- 

 cephalus exspinosus was not obtained for a time, but has subsequently been 

 realized to a gratifying degree. Of the two "low" lines, one has produced 

 only normal females for the last 8 successive generations, i. e., selection has 

 apparently eliminated the production of intergrades. The other low line 

 has produced no intergrades for the last 23 successive generations. On the 

 other hand, the two "high" lines continue to maintain their usual production 

 of intergrades. 



Sex in Relation to Metabolism in Pigeons. 



During the year Dr. Riddle has completed some studies on certain aspects 

 of sex and on the relation of "reproduction overwork" to sex in pigeons. 

 Most of these current studies have also been prepared for early publication in 

 various journals. Other results are being incorporated into a complete 

 account of his sex studies. 



Determination of Sex in Date-Palm Seedlings. 



During the past year considerable progress has been made in the date- 

 palm problem, the most important element of which has been the determina- 

 tion of the chromosome number. The problem was formulated and the 

 material collected by Dr. H. H. Laughlin, the cytological work done by 

 Misses Elizabeth Lord and Rachel Haynes. The haploid count has given 

 18 chromosomes. Material taken from plants, the sex of which is definitely 

 known, is being prepared for comparative studies in an effort to make an 

 early diagnosis of sex. Practically, the sex of seedling date-palms can not be 

 determined until the plant blooms at the age of 3 or 4 years. The purpose of 

 these studies is to seek a sex-diagnosis in the sprouting seedling, without 

 destroying the seedling itself. 



GERMINAL AND SOMATIC VARIATIONS. 

 Mutations and their Selection in Cladocera. 



Sex intergrades occur abundantly in certain lines of Daphnia longispina, 

 and the effectiveness of experiments on selection proves that mutations 

 frequently occur in sex-intergrade stock. One of the other mutant stocks, 

 the "excavated head" stock, has been similarly subjected to selection as a 

 method of analyzing the constancy or mutability of this character. Of 

 six strains (derived from sisters and at the start producing the mutant 

 character to an equal extent), three were taken for "high" strains and 

 three for "low" strains. Selection has proceeded for 65 generations. Of 

 the low strains, one showed in the second generation a lowering of the curve 

 of "degree of excavation," and the drop increased materially after the fifty- 

 ninth generation. Its present average grade of manifestation of the char- 

 acter is approximately one-eighth of its original average. Another low strain 

 showed an effect of selection after 10 generations and a further drop after 19 

 generations of selection. It now averages about one-fourth of its original 

 average manifestation. The third low strain showed no decided decrease 

 in manifestation of the character until after the fifty-fourth generation of 

 selection, and has shown no further drop. It now averages approximately 

 one-sixth of the original manifestation. Of the three high strains, two have 

 shown no decided increase in the manifestation of the character. The other 



