THE CIRRIPEDIA 



135 



retracted and enclosed in ;i new cuticle, remaining connected only 

 with the antennulc which is fixed to the host (Fig. 82, D). Within 

 the sac thus formed, a tubular chitinous organ known as the " dart " 

 becomes differentiated. At first the dart is invaginated into itself, 

 and in connection with it a second ciiticular sac iDecomes separated 

 within the first. The larva at this stage was designated by Delage 

 the "Kentrogon" (Fig. 82, E). The point of the dart lies within 



R. 







Via. S3. 



Sections throii;;li successive stages in development of the "nucleus" of the Sacculiiia. 

 ■interna, am, outer layer of niautle ; iin, inner layer of mantle ; m, mesoderm cells ; o, 

 aperture of invajiination of perisomatic cavity, not shown in B ; ov, rudiment of ovary; p, 

 l)erisomatic cavity. (After Delage, from Korschelt and Heider's Emhriiology.) According 

 to G. Smith, the mantle-cavity is already established when the invagination to form the peri- 

 somatic cavity takes place as in A. 



the fixed antennule, and when fully formed it becomes evaginated 

 and forces its way through the cuticle of the host (Fig. 82, F). 

 Through it the contents of the sac, consisting of a mass of 

 undifferentiated cells surrounded by an ectodermal lajer, jiass into 

 the body-cavity (liaemocoel) of the crab, and l)ecome what Delage 

 called the Sacculimt interna. Probably the mass of cells is at 

 first carried passively by the blood-currents of the host, but it 

 ultimately becomes attached to the lower surface of the intestine 



