THE DEVELOPMENT OF THE EXTERNAL FORM OF THE BODY. 185 



segments beside the primary cephalic segment, viz., those of the 

 antennae, of the jaws, and of the oral papillae thus take part in 

 the formation of the head. 



The head of the embryo, in consequence of the great development 

 of the cephalic lobes, at first appears very large in proportion to the 

 rest of the body (Figs. 86 and 89). In the course of development, 

 however, it decreases in size, the mouth shifts more to its anterior 

 end, and the form of the adult is thus practically attained. 



R. 



B. 



vo. 



ooa 



Fie. 94. — Anterior parts of embryos of P. Edwardsii, ventral aspect (after v. Kennel). 

 at, antenna; /,, the folds broken up into papillae, surrounding the month; /,, the folds 

 lying outside of/ ; y + vo, ganglion and ventral organ of the cephalic segment with the slit-like 

 depression <>f 1 1 1* • ventral organ ; k, jaws ; ol, upper lip ; op, oral papilla.' ; p , p lt , first and 

 second pairs of legs ; vo l -vo i , ventral organs of the jaws, oral papillae, an.' of the first two 

 trunk-segments; vo„ is divided into an anterior and a posterior part; x, prominences in 

 front of the antennal rudiments (pp. ISO and 1ST). 



The young are born ■ provided with the complete number of 

 limbs. Their development, according to authors, lasts unusually 

 long (Sedgwick, No. 11). P. novae-zealandiae is said to require 

 eight to nine months for its development, and P. capensis thirteen 

 months (?). The umbilical cord, which in the South American 

 species connects the embryo with the placenta, at the time when 

 the embryo lengthens and coils up its posterior end, changes and 

 finally degenerates ; its lumen closes first near the embryo. The 

 embryo is now nourished by swallowing the surrounding albumen, 



