ONTOGENY OF THE ANNULUS VENTRALIS. 



125 



plate lacks any groove and henceforth remains without any spe- 

 cial development. The female is also recognizable by the ap- 

 pearance of the short, curved 

 cuticular ridge on the base of 

 the third leg, each side of the 

 body, which is to be the me- 

 dian edge of the future orifice 

 of the oviduct. From this 

 superficial ridge a cylindrical 

 epithelial tube, the oviduct, 

 leads into the interior of the 

 body. The first abdominal 



FIG. 5. 



appendages, or pleopods, are 



blunt papillae and apparently 



the same in both sexes, though sometimes in the male they seem 



more pointed and possibly longer. 



The annulus is thus a narrow transverse part of the sternum 

 and since its posterior edge projects and overhangs somewhat it 

 might be regarded as a sort of transverse fold. Its surface is en- 

 tirely flat and simple as compared with the complex adult surface, 

 Fig. i, except for the slight median depression. Looking at the 

 shell only, Fig. 6 enlarged two hundred diameters, this depres- 

 sion is a wide shallow groove indicated by converging wrinkles 

 in the cuticle on each side the middle line of the animal and ex- 



FIG. 6. 



FIG. 7. 



tending forward but a slight distance from the posterior edge of 

 the annulus. The posterior edge of the annulus is rounded and 

 protuberant and the groove to some extent extends over this pos- 

 terior face of the annulus and cannot well be all seen at once from 

 a ventral point of view. While this groove in the shell differs in 

 different specimens it is in no way an artificial result of methods 



