632 GEOFFKEY SMITH. 



themselves by their antennulas to a hair upon any portion of 

 a young individual of the host, preferably upon the append- 

 ages. 



The Cypris casts off its thoracic appendages, the ectoderm 

 draws away from the shell, and conies to surround a mass of 

 mesodermal cells; it secretes a chitinous coat, and in this 

 manner the Kentrogon larva is formed. The Cypris shell, 

 together with all the larval organs, are thrown off. 



The ectoderm of the Kentrogon secretes a hollow dart in 

 the anterior region which projects up into the antennule b}" 

 which the larva is fixed to the base of the hair on the crab, 

 and gradually penetrates the base of the hair so as to open a 

 means for the cells contained in the Kentrogon to enter the 

 hcemoccel of the crab. 



The embryonic cells of the Kentrogon, consisting of ecto- 

 derm and mesoderm, enter the lia)mococl of the crab, and are 

 carried about in the blood-stream until they reach the large 

 blood-spaces surrounding the intestine. They are enclosed 

 in a thin chitinous cuticle. The Sacculina interna 

 migrans now proceeds to grow rapidly, to throw out roots 

 in all directions, while the central tumour grows down the 

 intestine towards the junction of thorax and abdomen of the 

 crab. As it grows in this manner, the adult organs are 

 differentiated in the most posterior portion of the central 

 tumour, which soon arrives at the position of evagination of 

 the adult Sacculina. Here differentiation proceeds, and the 

 pressure of the growing tumour upon the epithelium of the 

 crab causes it to degenerate, and thus, when the crab next 

 moults, a hole is left in the new chitin, through which the 

 Sacculina protrudes, and so gains the exterior. 



Literature. 



1. Delage, Y. — " Evohition de la Sacculine," 'Arcli. Zoo). Exper.,' srr. 2, 



t. ii, 1884. 



2. Smith, G. — ' Fauna des Golfes von Neapcl,' ]\loiiograi)li, No. 29, "Tlie 



llliizocepliala," 1906. 



3. Malaquin, a. — "Le Parasifisme J^volutif dcs Moustrillidcs," 'Arcli. 



Zool. Expcr.,' scr. 3, t. ix, 1901. 



