430 



CRUSTACEA ENTOMOSTRACA. 



itself to a young crab, most frequently (in the neighbourhood of Roscoff, 

 where Delage carried on his researches) to Carcinus moenas. 



The larva grasps the base of one of the crab's setae with one of its 

 antennae, and there remains attached (Fig. 276, C). The whole of the pos- 

 terior parts of the body of the larva including the swimming appendages 

 and their muscles, together with the eye, ganglion and excretory organs 

 now break down and are shed by rupture of the ectoderm. There remain 

 the ectoderm, which is rapidly made whole, the mass of primitive 



FIG. 277. Sacculina carcini in situ on the host (from Lang after a diagrammatic draw- 

 ing by Delage). hr branchial, d intestinal and I hepatic regions of the crab. Jcs the 

 body and p the pedicle of the Sacculina (external) ; m&basilar membrane from which the 

 roots of the parasite proceed throughout the body. 



ova and a small number of other mesoblastic cells (Fig. 276, D, E). 

 The bivalve shell of the Cypris stage is also shed, but the antenna 

 remains connected at its base with the new cuticle secreted by the 

 ectoderm, and still holding on to the seta. This process is com- 

 pleted in about 3 hours. The soft-parts now shrink away from the 

 anterior part of the old cuticle and form a new one within it. The 

 new cuticle is produced in front into a pointed process open at the end, 

 and behind is invaginated around the base of the process (Fig. 276, E). 

 At this stage the young Cirripede is known as the Kentrogon larva. As 

 growth proceeds the base of the process becomes evaginated, with the 

 result that its point is thrust forward along the hollow antenna (Fig. 

 276 F) and pierces the soft cuticle of the crab at the base of the seta to 

 which the larva is attached. The soft parts of the larva, consisting of the 

 mass of primitive ova and other mesoblast cells, surrounded by a layer of 

 ectoderm, now travel along the hollow process of the cuticle and enter the 

 body of the crab. 



