C. C. LiTTLK 285 



reported by DonaisUT, ami tomiH to hHow that the yellow animal tnius- 

 mitt^i to its pifM/e/iy no peculiar set of mfHiijiers. 



VI. An ATTF.MIT to explain the CXrUKHKNrK OK (a)STKHILK, ANI> 

 {h) KEHTILE TORTOISK-SIIKLL MAI.P>i. 



(rt) The prtHiuction of sterile tortvise-shell males. 



It is agnHMl by all th(>s(» who have n'|K)rte(l on brccciin^ oxpi^riinontsS 

 with cnt.s that the female apjK'ars to he homozygous, tin- male hetero- 

 zyginis, for sex. The former is therefore -Y-Y, the latter XO in formula. 

 This places aits in the siime category with Drosophila, and this in turn 

 means that one may rightfully turn, and in fact should turn, to the mag- 

 nificent work of Morgjvn and his associates in any attempt at explaining 

 a peculiar result which shows exceptional conditions of sex-linkage. 



If one considers the phenomena of non-disjunction of the X chromo- 

 some in Drosophila, reported by Bridges in 1918, and later (IDUI a and 

 6) further established by him after an extensive series of breeding ex- 

 periments, one cannot fail to be impressed by the similarity between the 

 results of that process in Drosophila, and the observed experimental 

 facts in cats. 



For example, non-disjunction is neither frequent in its occurrence 

 nor is it clear enough in its hereditary behaviour to give striking 

 numerical results in as slow breeding an animal as a cat, unless it were 

 watched for deliberately. In Drosophila it gives rise to two ver}- sig- 

 nificant exceptions to the normal sex-linked inheritance. First, it 

 produces animals apparently males, which are sterile, and second, mosaic 

 form^ are apt to arise in non-disjunctional stocks. If one considers that 

 the majority of tortoise-shell cats luhich are apparently males are stetnle, 

 and second that they are also a mosaic form in a sex where commonly 

 none is found, the comparison becomes interesting and extremely sug- 

 gestive. 



We may now consider what the probable results of non-disjunction 

 would be, did this phenomenon exist in cats. 



The chanicteristic of primary non-disjunction is that in oogenesis the 

 two A'' chromosomes go together into a single egg, leaving another egg 

 without even the normal single X. This may be shown Jis follows : 



Non-disjunctional female XX 

 forms gametes A'A' and - 



