358 THE ZOOLOGIST. 
fertilisation will turn a female into a male or the reverse. It may 
therefore be regarded as established in very many cases that from the 
moment of fertilisation at least, and sometimes in the unfertilised 
egg, the sex is irrevocably determined. The problem had reached this 
stage when M‘Clung, Wilson, and others discovered that in certain 
insects the males and females contain different numbers of chromo- 
somes in the germ-cells before maturation, the females having an even 
number and the males one less. After maturation there are two 
kinds of spermatozoa, one containing the same number as the mature 
egg, and the other having one chromosome missing. It was ab first 
suggested that at fertilisation the spermatozoon having the larger 
number caused the egg to develop into a female, that with the smaller 
number male; but Wilson’s later suggestion is that there is selective 
fertilisation, that the eggs are either male or female, and that male 
eggs are fertilised by spermatozoa having no heterochromosome, 
female eggs by those which have it. Morgan has recently found 
that in a species of Phylloxera there are two kinds of spermatids, one 
of which has one chromosome more than the other. Those with the 
smaller number degenerate; those with the larger develop into func- 
tional spermatozoa, and all fertilised eggs become females. Recently 
important evidence has been obtained from breeding experiments with 
Lepidoptera, fowls, &c. In the moth Abraxas grossulariata there is 
a rare variety, lacticolor, which is found usually only in the female. 
It is a Mendelian recessive, so that when paired with a typical male 
all the offspring are typical grossulariata. 
‘‘Hixperiments in Inheritance.” —Interim Report of the Com- 
mittee, consisting of Prof. W. A. Herdman (Chairman), Mr. Douglas 
Laurie (Secretary), Mr. R. C. Punnett, and Dr. H. W. Marrett Tims. 
(Drawn up by the Secretary.) 
On the Inheritance of Yellow Coat Colour in Mice.—Reasons for 
this Research.—The primary reason for this research is the unexpected 
result obtained by Cuénot on cross-breeding yellow mice with mice of 
other colours. On mating a yellow mouse with one that was grey, 
black, or chocolate, Cuénot always found yellowness to act as a 
heterozygous Mendelian dominant to the other colour. When yellow 
F' hybrids so produced were intercrossed they gave an F' generation 
much in accord with expectation, being composed roughly of three 
yellows to one recessive. It is the gametic constitution of these 
extracted yellows which gives cause for surprise, and which is the 
essential point of importance. Highty-one of them were tested by 
breeding, and it was to be expected that of these twenty-seven or so 
would be homozygous for yellowness, but not even one fulfilled the 
conditions of Mendelian purity. ‘Or, 4 mon grand étonnement,”’ 
says Cuénot, “je n’en ai pas trouvé une seule; les quatre-vingt-un 
souris étaient toutes également hétérozygotes.” 
This important and interesting result has attracted explainers of 
different schools. Morgan makes it a text for emphasizing his views 
about ‘‘ Contamination.” Purity, in the Mendelian sense, he denies. 
‘Purity,’ he says, ‘is dominance over latency.” Cuénot, on the 
other hand, supported by Wilson and favoured by Lock, suggests 
that pure yellow-bearing germ-cells of both kinds are indeed formed 
