276 
GEOFFREY S:\HTH. 
It is ot' consideraLle interest to note that exactly the same 
difference between the sexes occurs in the salmon, where the 
same two pigments are found exercising much the same func- 
tion as in the crab. The male salmon in the breedino; season 
has a deeper pink skin coloration than the female, which 
stores up lutein and tetronerythrin in the ovary. 
The principal difference between the salmon and the crab lies 
in the fact that in the salmon the pigments and fats are trans- 
ferred from the muscles, while in the crab they come directly 
from the liver. 
We must now inquire what effect Sacculina exerts on the 
formation of these pigments in the crab. 
The colour of the shell of infected individuals is of the 
dull green and brown tint found in females without the bright 
red characteristic of the male. The blood of Carcinus 
infected with Sacculina is invariably colourless or else faintly 
tinged with yellow. The liver, on the other hand, is con- 
stantly of a bright yellow colour, and this colour is exhibited 
with far more constancy than in any other category of crabs, 
except normal females which are maturing the ovary aud 
have yellow blood. Considerable importance may be attached 
to this fact, as it indicates that the presence of Sacculina 
stimulates the liver to the active formation of the yellow 
lutein. The fact that this substance does not flood the blood 
of the Sacculinised crabs in the same way that it floods the 
blood of the maturing female, may be ascribed to the rapidity 
with which the Sacculina roots seize on the lutein and its 
accompanying fat and abstract it from the blood. 
I have never observed a Sacculinised crab with red blood, and 
in this respect the observations of Robson on Inachus infected 
with Sacculina are very puzzling. Robson (3) observed that 
a very large percentage of Sacculinised Inachus possessed 
red blood, and though his observations on the livers of 
infected Inachus agree very well with what occurs in 
Carcinus, it is very difficult to explain the presence of tetron- 
erythrin in the blood of infected individuals. 
If it should prove that this tetronerythrin is only masking 
