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This paper includes the first published attempt to explain the inheritance of tortoiseshell and related coat colours in cats. Even though Doncaster's explanation was not correct in relation to Black and Orange, he was correct in concluding that Blue and Cream are dilute versions of Black and Orange. 

Doncaster starts by stating "It is well known that Tortoiseshell cats are almost always female , and it is commonly said that the corresponding colour in male is orange (otherwise described as red or yellow)." In order to investigate this unusual phenomenon, he wrote to cat breeders, asking for the results of matings involving these coat colours. 

From a summary of the results of a wide range of matings received from his correspondents, he concludes "From these facts it is clear that tortoiseshell is a heterozygous form", which is still the understanding today.

He then attempts to explain why tortoiseshells are "almost exclusively females", hypothesising that "The answer appears to be that in the male orange is completely dominant over black, while in the female the dominance is incomplete, and tortoiseshell results." Given that the existence of X and Y chromosomes was not yet known, this was a reasonable explanation.

Interestingly, Doncaster had also received information on matings involving cream and blue coat colours. He concluded that "These two colours appear to be dilute forms of orange and black, and have exactly similar relations to one another." This interpretation, which, in effect, is the first mention of the effect of what is now called the Dilution gene, has stood the test of time.