332 
SEXUAL SELECTION. 
Part II. 
distinguished from all other ampnipods by the females 
having “ the coxal lamellae of the penultimate pair of 
“ feet produced into hook-like processes, of which the 
“ males lay hold with the hands of the first pair.” The 
development of these hook-like processes probably 
resulted from those females which were the most 
securely held during the act of reproduction, having- 
left the largest number of offspring. Another Bra- 
zilian amphipod ( Orchestia Darwinii, fig. 7) is de- 
scribed by Fritz Muller, as presenting a case of dimor- 
phism, like that of Tanais; for there are two male 
forms, which differ in the structure of their chelae. 8 As 
chelae of either shape would certainly have sufficed to 
hold the female, for both are now used for this purpose, 
the two male forms probably originated, by some having 
varied in one manner and some in another ; both forms 
having derived certain special, but nearly equal advan- 
tages, from their differently shaped organs. 
It is not known that male crustaceans fight together 
for the possession of the females, but this is probable ; 
for with most animals when the male is larger than the 
female, he seems to have acquired his greater size by 
having conquered during many generations other males. 
Now Mr. Spence Bate informs me that in most of the 
crustacean orders, especially in the highest or the 
Brachyura, the male is larger than the female; the 
parasitic genera, however, in which the sexes follow 
different habits of life, and most of the Entomostraca 
must be excepted. The chelae of many crustaceans are 
weapons well adapted for fighting. Thus a Devil-crab 
( Porhmus piiber ) was seen by a son of Mr. Bate fighting 
with a Carcimts msenas, and the latter was soon thrown 
on its back, and had every limb torn from its body* 
Fritz Muller, ‘Facts and Arguments for Darwin,’ 1869, p. 25-28. 
