| OCR Text |
Show 332 SEXUAL SELECTION. PART II. distinguished from all other am phi pods by the females having "the coxal lamellre of the penultimate pair of "feet produced into book-like processes, of which the "males lay hold with the hands of the first pair." The development of these book-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 Brazilian amphipod (Orchestia Darwinii, £g. 7) is described by Fritz Muller, as presenting a case of dimorphism, like that of Tanais ; for there are two male forms, which differ in the structure of their chelre.8 As chelre of either shape \Yould 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, bnt nearly equal advantages, 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 chelre of many crustaceans are weapons well adapted .for fighting. 'l'hus a Devil-crab ( Portunus puber) was seen by a son of Mr. Bate fighting with a Oarcinus rnmnas, and the latter was soon thrown on its back, and had every limb torn from its body. 8 Fritz Milllcr, 'Facts and Arguments for Darwin,' 1869, p. 25-28. Crr.A.P. IX. CRUSTACEANS. 333 When several males of a Brazilian Gelasimus, a species furnished with immense pincerf:, were placed too-ether by Fritz Muller in a glass vessel, they mutilatet:>d and killed each other. Mr. Bate put a large male Oarcinus Fig. 7. Orchcstia. Darwinii (from Fritz Miiller), showing the differently-constructed chelre of the two male forms. rn~nas · into a pan of water, inhabited by a female paired w1th a smaller male; the latter was soon dispossessed but, as Mr. Bate adds, " if they fought, the victor |
