STUDIES IN THE EXPERIMENTAL ANALYSIS OF SEX. 253 
may remain colourless for some time after these processes, 
but gradually as the crab approaches the period of a new 
moult or of the formation of a fresh batch of eggs, lipochrome 
accumulates in the blood in a manner characteristic for each 
sex. In the male sex the pink lipochrome invariably pre- 
ponderates, so that the blood of the male is charac- 
teristically of a salmon-pink colour ; in the female sex, 
on the other hand, the yellow lipochrome preponderates 
very strongly over the pink, and this is most markedly 
the case when the female is ripening the ovary and 
storing up the lutein in it. Often intermediate orange 
colours appear in both sexes, due to an intermixture of the 
two pigments, but in the vast majority of cases the blood of 
the male is either colourless or pink, that of the female 
colourless or yellow. That the appearance of the brilliant 
yellow colour in the blood of the female is strictly associated 
with the ripening of the ovary has been completely settled 
by Robson and myself, and in this respect we agree with 
Heim’s observations on a number of other Decapod Crustacea, 
but the occurrence of the pink lipochrome in the male sex at 
the periods leading up to the moult is no less certain, though 
Heim appears to have missed it. And it must be admitted 
that at first sight the occurrence of the lipochrome in the 
normal male, which, as far as intensity of colour is concerned, 
appears to be present in quantities equal to that in the female, 
offers a serious difficulty to our hypothesis. For it would 
seem to indicate that periodically the male blood is charged 
with fatty material to the same extent as the female. 
An unexpected light has been thrown upon this difficulty by 
a series of quantitative estimations of the fat-content of the 
blood of Carcinus maenas which I have recently made. 
The method which I have used in making these estimations is 
one which is recommended by Professor Leathes in his book 
on the fats (2), and my exact mode of procedure is as 
follows : About 20 gr. of blood is drawn from a number of 
crabs and accurately weighed on a chemical balance into a 
porcelain dish. An equal weight of a 130 per cent, solution 
