THE GENETIC SIGNIFICANCE 

 OF INTRA-UTERINE SEX RA- 

 TIOS AND DEGENERATING 

 FETUSES IN THE CAT 



E. E. Jones 



Carnegie Institiitdon of Washington 

 Cold Spring Harbor, Long Island, N. Y. 



DURING the past year the work 

 was undertaken of examining the 

 uteri of pregnant cats, wath the 

 hope of throwing some Hght on several 

 questions which are of interest from 

 the genetic point of view. Through 

 the courtesy of the Society for the 

 Prevention of Cruelty to Animals in 

 New York City it was possible to do 

 this. The routine procedure was as 

 follows : as the dead cats were removed 

 from the gas tank in which they were 

 asphyxiated, any females which showed 

 evidences of pregnancy were put aside. 

 These were then dissected, and records 

 taken of the coat color of the mother, 

 the number of fetuses, and sex of those 

 present in each horn of the uterus, as 

 well as the coat color whenever the 

 embryo was sufficiently developed to 

 show definite color pattern. The oc- 

 currence of any structural abnormality 

 was noted, but these were found to be 

 extremely rare. A few polydactylous 

 animals were found. In each case 

 where this occurred, some of the fe- 

 tuses also exhibited the abnormality. 

 One female was discovered to have a 

 cystic ovary on the left side. The left 

 tube of the uterus contained a degen- 

 erating fetus. This case has not been 

 considered pathological, however, in 

 the calculation of the data, since we 

 have no knowledge of the influence of 



such an ovary on the surrounding 

 tissues. Another case, that of a 

 female in which a teratoma-like struc- 

 ture was found, is considered in detail 

 in a later paragraph. 



Doncaster^ suggested that the oc- 

 currence of tortoiseshell males in cats 

 and their usual sterility, might be 

 due to hormone action somewhat 

 similar to that apparently involved in 

 the production of free-martins in cat- 

 tle.^ 148 pregnant cats were examined 

 with a total of 653 embryos. In- 

 spection of the uteri showed no 

 sign of anastomosis of the circulatory 

 systems supplying the fetuses in any 

 case. This body of negative evidence 

 makes the correctness of Doncaster's 

 hypothesis seem extremely doubtful. 



Of the 653 embryos, sex was deter- 

 mined in 613. The ratio was found to 

 be 122. 10 ±8. 30. This is very much 

 higher than that usually found in 

 mammals when it is determined at 

 birth. It is interesting, however, to 

 compare this figure with that found by 



Jewell^ 



m 



fetal cattle of 123.21, 



These data are analogous, both being 

 based entirely on embryos during intra- 

 uterine development. Comparison of 

 this fetal ratio with existing sex ratios 

 in cattle shows a wide variation. 

 Wilckens^ has given the ratio at or 

 near the time of birth as 107.3. 

 Pearl and Parshley^ give the ratio 



' DoNCASTER, L. The Tortoiseshell Tomcat — ^A'Suggestion. J. of Genetics, Vol. IX. 1920. 



- LiLLiE, F. R. The Free-Martin; a Study of the Action of Sex Hormones in the Fetal Life of Cat- 

 tle, /. Exp. Zool. XXIII. 1921. 



3JEWELL, F. M. Sex Ratios in Fetal Cattle. Biol. Bull. XLX. 1921. 



^ WiLCKENS, M. Unteruchungen uber das Geschlechtsverhaltnis und die Ursachen der Ge- 

 schlechtsbildung bei Haustieren. Biol. Centrabl. Bd. VI. 1887. 



i Pearl, R. and H. M. Parshley. Data on Sex Determination in Cattle. Biol. Bull. XXIV. 1913. 



