REPRODUCTIVE HISTORY OF THE MOLE. 209 
curious one—though it must be remembered that it has its 
parallel in general mammalian, and even in human development. 
The Mullerian ducts open first into a cloacal uro-genital sinus ; 
at a later stage this opening is lost and the lumen of the ducts 
becomes obliterated. The Mullerian ducts become mere Mul- 
lerian cell-strands, and these cell-strands pass forwards below the 
urethral floor, and mesial to the crura clitoridis, towards the base 
of the genital tubercle. It is at the base of the genital tubercle 
that the uro-genital sinus approaches nearest to the surface of 
the body, and here a proliferation of surface epithelium dips in 
towards it. 
This epithelial invasion is crescent-shaped in outline (correspond- 
ing with the base of the genital tubercle), and the extremities 
of the crescent dip into the perineal tissues and meet the 
Mullerian epithelial strand. In the embryos examined the right 
horn of the crescent in one case, and the left in the other, alone 
extends inwards to the termination of the Mullerian strand. 
E. Postnatal Stages of Internal Genitalia. 
(i.) The Nestling Mole. 
The young mole is born in a naked and rather immature 
condition, and although the growth within the first few days of 
life is extraordinarily rapid, it is not until about the 9th day 
that the colour changes from the primitive pink to the dull lead- 
colour that marks the advent of hair. At about the end of the 
first fortnight the actual hair appears. 
This period of life has been fully observed from the field- 
naturalist’s point of view by Adams, Cocks, and Evans (all quoted 
by Barrett-Hamilton, 7). 
It was obvious from the outset of my investigation that the 
nestling period was one of the utmost importance, for it was 
evident that it was not only a time of extremely active body 
growth, but that remarkably rapid internal changes must be 
taking place as well. Indeed there may be said to be two 
well-marked phases of wonderfully rapid evolution in the repro- 
ductive system of the mole, the one being present during this 
nestling period, and the other being marked by those almost 
violent changes which occur during the short but intense period 
of sexual activity. 
I have found specimens of nestling moles particularly difficult 
to obtain, and during two breeding seasons I have failed to find 
nestlings, although I have had adults in all phases of sexual 
activity. For the only material which I have been enabled to 
examine microscopically in serial sections, I am indebted to 
Professor L. Doncaster. This material, which consisted of two 
specimens, is of interest, for the nestlings were presented to the 
Cambridge University Museum of Zoology by the Rev. Leonard 
Jenyns, and had been in their bottle of spirit for at least some 
Proc. Zoo. Soc.—i914, No. XIV. 14 
