18 THE ZOOLOGIST. 
almost impossible to see the animals, even when they emerge 
from cover. 
The length of the River Crayfish is about three or four 
inches, though they sometimes exceed this. I have two speci- 
mens which are nearer six inches in length, with claws nearly 
an inch in width; but this size is very unusual, as I never saw 
many s0 large, although I have caught, or seen caught, many 
thousands of crayfishes. 
The carapace is granulated, and the regions are well 
marked; the rostrum is pointed, with a spine on either side. 
The first pair of legs, or “‘ claws,” are massive and nearly equal 
in size, but often through injury they are very unequal, as is 
the case with marine crustaceans; the second and third pairs 
of legs are didactyle, and their owner makes very good use of 
them when foraging about at the bottom of his native brook. 
The eggs of this species are very large in proportion to the 
animal, consequently there are fewer of them to one parent than 
is the case with most other crustaceans; in fact, the eggs of 
Astacus fluviatilis, an animal four inches in length, are indi- 
vidually about four times the size of the eggs of the Sea Cray- 
fish, Palinwrus vulgaris, which is an animal reaching a foot in 
length, but which has reached (as I have measured) the enor- 
mous size of over two feet from rostrum to tail. But the 
number of eggs carried by the latter is tremendously in excess 
of the number carried by the former, and the reason is, 
I think, not far to seek. The Sea Crayfish, in consequence 
of its habits and surroundings, is at a great disadvantage in 
propagating its species, for considering what its zoea is, and 
also that it is a favourite food, until it is old enough to fight 
its own battles, for a number of fishes and other natural 
enemies, the wonder is that any reach maturity at all. Astacus 
frwiatilis has more victims than enemies; the narrow water- 
courses in which it lives contain but few foes, perhaps the 
only one being fish, and, so far as I have noticed, fish were 
not abundant in crayfish-brooks; besides, the Crayfish burrows 
into the clay-banks of its brook, and, as we have already seen 
with regard to the marine Crustacea, burrowing species carry 
but few ova. 
As Prof. Huxley remarks, Astacus fluviatilis is usually found 
in water-courses of a calcareous district, especially when such 
