Body Colour in Amphipods and Isopods. 161 
that the food pigments pass directly as such into the blood plasma. Heim (13) 
showed that an excess of yellow pigment is present in the blood of female 
crabs at the time of ripening of the ovaries; once the eggs are expelled the 
blood loses its yellow colour. G. Smith (14) and Robson (15) have amplified 
these results, and in particular have shown that the presence of the yellow 
pigment corresponds with an increased percentage of lipoid in the blood. 
In this connection it is important to note that the distinction between the 
blue and the yellow forms of Orchestia does not depend on sexual difference, 
for both varieties occur in the male sex. 
In order to see whether one variety would pass into another, I kept four 
blue and four yellow examples of male Orchestia immersed in sea-water, 
without food, for a period of twenty-six days. At the end of that time the 
animals were removed alive and healthy, but all retained their original 
colour. 
While the plasma of some amphipods is decidedly blue, I have hitherto 
come across no isopods with any trace of blue in their blood. The blood of 
the Oniscoidea seems to be devoid of colour. 
WHITE GAMMARI. 
Associated with ordinary specimens of Gammarus marinus on the beach 
one occasionally comes across a pale specimen, whose colour varies from light 
yellow almost to white. The first time I found these animals, on the seaward 
side of a storm-beach through which fresh water slowly percolated, they were 
quite numerous. A year later, at the same place, I found them equally 
numerous. As a rule, however, they are rare; but they do occur widely 
distributed round the coast. I have found them in the extreme north of 
Scotland and in the south of England. 
When the antennz of these animals are viewed with the microscope, the 
circulating fluid is seen to swarm with very fine particles much smaller than 
blood corpuscles, which, however, are also present though greatly reduced in 
number. The appearance presented by these particles escaping from a 
wound in the antenna reminds one of dry sand pouring from an orifice. 
They have none of that adhesive property which is such a marked feature 
in extravasated crustacean blood cells, and do not form a plug at the mouth 
of the wound (see Tait, 1). The blood corpuscles eventually arrest the 
hemorrhage by agglutinating at the site of the wound, but these small 
particles do not get caught in the adhesive mass of cells thus formed. 
The escaped fluid when viewed against a dark background is milk-white. 
The plasma itself is colourless, and the whiteness is due to dispersion of light 
from the surface of the multitudinous particles. 
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