Chap. VIII. SEXUAL DIFFEEENCES IN AMPHIPODA. 79 



anterior feet (gnathopoda, Sp. Bate) and in the Hype- 

 rinae in the structure of the antennae, is often so great 

 that males and females have been described as distinct 

 species, and even repeatedly placed in different genera 

 (Orchestia and Talitrus, Cerapus and Bercotlioe, Lestri- 

 ff onus and Hyperia) or even families {Hy]perines anor^ 

 males and Hyi^erines orclinaires). Nevertheless it is 

 only developed when the animals are nearly full-grown. 

 Up to this period the young resemble the females in a 

 general way, even in some cases in which these differ 

 more widely than the males from the " Type " of the 

 order. Thus in the male Shore-hoppers (Orcliestia) the 

 second pair of the anterior feet is provided with a 

 powerful hand, as in the majority of the Amphipoda, 

 but very differently constructed in the females. The 

 young, nevertheless, resemble the female. Thus also, — 

 and this is an extremely rare case," — the females of 

 Brachyscelus are destitute of the posterior (or inferior) 

 antennae; the male possesses them like other Amphi- 

 podcc; in the young I, like Spence Bate, can find no 

 trace of them. 



It is, however, to be particularly remarked, that the 

 development of the sexual peculiarities does not stand 

 still on the attainment of sexual maturity. 



For example, the younger sexually mature males of 

 Orcliestia Tueurauna, n. sp., have slender inferior an- 

 tennae, with the joints of the flagellum not fused toge- 

 ther, the clasping margin (" palipa^,'" Sp. Bate) of the 



^4 " I know of no case in which the inferior (antennae) are obsolete, 

 when the superior are developed," Dana. (Darwin, ' Monograph on the 

 Subclass Cirripedia, Lepadidse,' p. 15.) 



