Chap. IX. 
CRUSTACEANS* 
331 
is gained by tlieir inequality in size on the opposite 
sides of the body, and by the inequality being much 
greater in the male than in the female ; and why, when 
they are of equal size, both are often much larger in 
the male than in the female, is not known. The chelae 
are sometimes of such length and size that they cannot 
possibly be used, as I hear from Mr. Spence Bate, for 
carrying food to the mouth. In the males of certain fresh- 
water prawns (Palsemon) the right leg is actually longer 
than the whole body . 6 It is probable that the great size 
of one leg with its chelae may aid the male in fighting 
with his rivals ; but this use will not account for their 
inequality in the female on the opposite sides of the body. 
In Gelasimus, according to a statement quoted by Milne- 
Edwards , 7 the male and female live in the same burrow’, 
which is worth notice, as shewing that they pair, and 
the male closes the mouth of the burrow with one of its 
chelae, wdiich is enormously developed ; so that here it 
indirectly serves as a means of defence. Their main 
use, however, probably is to seize and to secure the 
female, and this in some instances, as with Gammarus, 
is known to be the case. The sexes, however, of the 
common shore-crab ( Garcinus msenas ), as Mr. Spence 
Bate informs me, unite directly after the female has 
moulted her hard shell, and when she is so soft that she 
would be injured if seized by the strong pincers of the 
male ; but as she is caught and carried about by the 
male previously to the act of moulting, she could then 
be seized with impunity. 
Fritz Muller states that certain species of Melita are 
6 See a paper by Mr. C. Spence Bate, with figures, in 4 Proc. Zoolog. 
Soc.’ 1868, p. 363 ; and on the nomenclature of the genus, ibid. p. 585. 
I am greatly indebted to Mr. Spence Bate for nearly all the above 
statements with respect to the chelae of the higher crustaceans. 
7 4 Hist. Nat. des Crust.’ tom. ii. 1837, p. 50. 
