630 GEOFFREY SMITH. 



point are transported to the position of the Sacculina 

 interna migrans. Delage, who did not observe the latter 

 stage^ believed that the cells of the Kentrogon, on entering 

 the crab, at once began to send out roots, and to grow always 

 in a determinate direction until the central tumour reached 

 the point where the adult Sacculina was to be evaginated. 

 But, since the youngest Sacculinae of the migrant stages 

 which I observed were not provided with elongated roots 

 stretching to the skin at any point where the Cypris might 

 have fixed, I incline to the opinion that the embryonic cells 

 of the Kentrogon, after entering the hasmocoel, are carried 

 passively about in the blood stream until they, sooner or 

 later, reach the large blood spaces surrounding the intestine, 

 and that, arrived there, they begin to throw out the root 

 system, while the central tumour grows down toward the 

 junction of thorax and abdomen where the body of the 

 Sacculina externa is differentiated. The method of this 

 differentiation, the formation of the adult organs, and the 

 evagination of the Sacculina to the exterior have been full}^ 

 described by Delage (1) and myself (2). 



The life-history of Peltogaster, the only other of the 

 Rhizocephala that has been at all Avorked out (2), is very 

 similar to that of Sacculina, save that it seems probable that 

 the Cypris fixes upon the abdomen of the hermit-crab, and 

 that the migrant phase of the internal development is not so 

 marked. 



The life-history of Sacculina may be shortly summarised as 

 follows : 



The eggs undergo maturation in the brood pouch, and are 

 self-fertilised. 



Development up to the Nauplius stage proceeds in the 

 brood pouch. 



The Nauplii are expelled to the exterior, and lead a 

 free-swimming existence for four days, undergoing four 

 moults. 



The Cypris stage is attained at the fifth day, and, after two 

 or throe days of free existence, the Cypris larva? attach 



