CTPRIS LARVA OF SACCULINA CARCINI. 



629 



After the formation of the Keutrogoii larva with its dart, 

 a process obviously preparatory to the infection of the host, 

 the next stage in the life-history which is known is that 

 which I have described (2, p. 47) under the name Sacculina 

 interna migrans. 



The parasite at this stage consists of a mass of embryonic 

 cells undergoing rapid division by mitosis; it has an irre- 

 gular shape, a few small roots beginning to grow out from a 

 central tumour, and the whole is enclosed in a thin chitinous 

 cuticle. There is no visible differentiation of any of the 

 adult organs. It is clear that the gap between this stage 

 and the Kentrogon larva is very slight, since the morpho- 



Em 



Text-figs. 1 and 2. — 1. Nauplius of Sacculina. 

 2. Cvpris of Sacculina. 



logical structure is practically identical. These small migrant 

 Sacculinas were found in the haemocoel of the ci'abs applied 

 to the upper part of the intestine just below the stomach, 

 that is to say, far away from the point where the body of the 

 adult Sacculina externa is situated. This position of the 

 earliest known internal stage of Sacculina is completely in 

 accord with the indefinite position of the fixation of the 

 Cypris larvae upon the crab, and is irreconcilable with the 

 theory that the Cypris fixes upon the under surface of the 

 crab's abdomen, and is transformed into the adult Sacculina 

 in situ. 



We are still confronted with the problem how the cells of 

 the Kentrogon that enter the hgemocoel of the crab at any 



