127 



SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally INVERTEBRATA and CRYPTOGAillA), 



MICKOSCOPY Etc.* 



ZOOLOGY. 



VERTEBRATA. 



a. Embryology, Evolution, Heredity, Reproduction, 

 and Allied Subjects. 



Inbreeding; and Sex-Ratio in Albino Rats. — Helen Dean KiNa 

 {Journ. Exper. Zool., 1918, 27, 1-35, 1 fig.). The normal sex-ratio in 

 the stock experimented with was 105 males to 100 females. In inbreed- 

 ing without selection there was in six generations little change. In 

 inbreeding further with females from litters with an excess of males the 

 ratio rose above the norm, except in the tenth generation. In the 

 eleventh generation it was 145 males to 100 females. The first twenty- 

 five generations of this series comprised 1752 litters, with 1:3,11G 

 individuals, 7116 males and 6000 females, the total ratio being 117 

 males to 100 females, 12 points above the norm. In this series the- 

 breeding females were selected from litters containing an excess of males. 

 In a second series, where the breeding females were taken from litters 

 containing an excess of feiqales, the deviation from the norm was in 

 the reverse direction ; for the entire group of 794 litters the sex-ratio 

 was 82 males to 100 females, 23 points below the norm. Through 

 selection the inbred strain was thus separated into distinct lines, and it ' 

 will be seen that selection had the greater influence on the female line. 

 The experiments seem to indicate that the female has more influence in 

 determining . the sex-ratio than has the male. " Yet it is not in the 

 differentiation of the ova, nor in the development of the spermatozoa, 

 that the key to the riddle of sex-determination will be found. A know- 

 ledge of the interaction of the germ-cells, and of the conditions that 

 influence it, must be gained before the final solution of this problem can 

 be attained." J. A. T. 



* The Society does not hold itself responsible for the views of the authors 

 of the papers abstracted. Tha object of this part of the Journal is to present 

 a summary of the papers as actually published, and to describe and illustrate 

 Instruments, Apparatus, etc., which are either new or have not been previously 

 described in this country. 



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