222 



CRUSTACEA. 



The abdomen {ah) is very rudimentary, consisting of a single joint 

 bearing two furcal appendages. The first antenna (i) is witliout 

 sucking disc and cement-gland. It consists of three joints : a basal 

 joint which is broadened and connected with the chitinous apodemes, 

 a long middle joint, and a short, terminal joint provided with three 



Fig. 107. — Consecutive larval stages of Sacculina carcini (after Delage, from Lang's Text-book). 

 A, Nauplius after tlie first moult. 11, free-swimuiing Cypris stage. C, Cyj^ris stage after the 

 larva has become attached to a seta (hb) of the host. D, formation of the Kcntrogon larva. E, 

 the Kentrognn larva after the Cypris shell has been thrown off and the arrow has formed. 

 F, the arrow has bored through the chitinous cuticle of the host. 1, 2, 3, the three pairs 

 of Nauplius limbs ; I-VI, thoracic limbs ; ah, abdomen ; bh, seta of the host ; /, fat globules ; 

 fs, frontal sensory organ ; rjl, glands of the frontal horns ; ov, rudiment of the ovary ; ff, 

 arrow; va, Nauplius eye. 



hooked setae. The Nauplius eye (wa) persists, but the paired eyes 

 are absent. Among the internal organs present at this stage, we 

 note the very distinct ovarian cell-mass {ov), the strongly-developed 

 musculature, the persistence of the glands of the frontal horns (yZ), 

 and the accumulations of jDigment and of food-yolk (/), 



