STL'MKS Ix\ TIIK KXrERlMKN'rAL ANALYSIS OF SEX. 275 
We must conclude from this that all the green and 
black pigment in the shell of Carcinus is formed from the red 
lipochrome, tetronerythrin, and that the yellow lutein does 
not occur in this situation. The fact that the green and 
black colours in the shell of Carcinus is formed from tetron- 
erythrin in combination with some other substance is shown 
also in the familiar fact that boiling for some time in water 
converts all the pigment in the shell to a bright red, and this 
red pigment can be extracted with alcohol and shown to be 
tetronerythrin. 
The liver of Carcinus yields a very large quantity of the 
yellow lutein, and either none, or else a mere trace, of the red 
tetronerythrin. Nevertheless it seems certain that the seat of 
formation of the tetronerythrin is the liver, since flecks of it 
can be often detected in this organ, quite distinct from the 
pale yellow of the general coloration. 
In the blood both pigments may occur together, but, as has 
been already pointed out, a great excess of yellow lutein is 
characteristic of the maturing female, and a great excess of 
red tetronerythrin is characteristic of individuals approaching 
the period of a moult, especially the males. The ovary of the 
female during its early stages of growth and pigmentation 
contains almost entirely lutein, but towards the end, when the 
eggs are ripe, a considerable amount of tetronerythrin is 
deposited in them as well. 
The fact that the adult female in preparing for reproduc- 
tion is constantly mobilising fatty material accompanied with 
the yellow lutein, whereas the adult male simply forms tetron- 
erythrin for the skin, gives us a simple explanation of the 
difference in external coloration which distinguishes the 
adult males from the adult females in Carcinus. This dis- 
tinction lies in the fact that the shell of the adult male is 
always redder than that of the adult female, especially at the 
joints of the appendages and on the under-surface, and this 
difference can obviously be accounted for by the excess of red 
pigment present in the male^s blood, and its replacement in the 
female by the yellow lutein which is destined for the ovary. 
