CRUSTACEA SEXUAL DIMORPHISM 



379 



"seizers." The former have numerous olfactory filaments on the antennae, the 

 latter much larger and very movable pincers on the chelate feet. In the Decapodan 

 males, the most anterior pair or the two most anterior pairs of pleopoda seem trans- 

 formed in order to assist in copulation. In the crayfish for example, they serve as 

 tubes or channels for conducting the spermatophores away from the genital aperture 

 to their destination. The other pleopoda which in the female carry the fertilised 

 eggs are reduced in the male, or may be, as in the Brachyura, entirely wanting. In 



FIG. 254. A, Adult male of Cancrion miser (nearly related to Portunion Fig 253, after 

 Giard and Bonnier), r, Rostrum ; 01, anterior antenna ; th, thorax ; I, liver ; 7i, testis ; Tie, heart ; 

 ab, abdomen. B. Hatched embryo of Portunion Maenadis (after Giard and Bonnier) from the 

 ventral side. t 2 , limb of the 2d ; ti, of the 7th thoracic segment ; 03, 2d antenna ; pZ 1; 1st ; 

 p?6, 6th pleopod ; au, eye. 



the Decapodan males also the chelae of the chelate feet are more strongly developed 

 than in the female. 



Adaptations for the Care of the Brood. It rarely happens in the Crustacea that 

 the female simply lays the eggs, attaching them to some foreign object and leaving 

 them to their fate. We find almost everywhere, on the contrary, that the females 

 retain the eggs on or in their own bodies in such a way that they are protected and 

 often also nourished by the mother body. The eggs develop under the protection 

 of the mother body, till the larvae or young Crustaceans are hatched, and even 

 these occasionally remain for some time in their birthplace. 



