Chap. IX.] CRUSTACEANS. 323 



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 con- 

 quered 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, how- 

 ever, 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 fight- 

 ing. Thus a Devil-crab {Portunus puber) was seen by a 

 son of Mr. Bate fighting with a Carcinus mamas, and the 

 latter was soon thrown on its back, and had every limb 

 torn from its body. When several males of a Brazilian 

 Gelasimus, a species furnished with immense pincers, were 

 placed together by Fritz Miiller in a glass vessel, they 

 mutilated and killed each other. Mr. Bate put a large 

 male Carcinus mamas into a pan of water, inhabited by 

 a female paired with a smaller male ; the latter was soon 

 dispossessed, but, as Mr. Bate adds, " if they fought, the 

 victory was a bloodless one, for I saw no wounds." This 

 same naturalist separated a male sand-skipper (so common 

 on our sea-shores), Gammarus marinus, from its female, 

 both of which were imprisoned in the same vessel with 

 many individuals of the same species. The female, being 

 thus divorced, joined her comrades. After an interval the 



8 Fritz MUller, ' Facts and Arguments for Darwin,' 1869, pp. 25-28. 



