RELATION OF ARTHROPOD HEAD TO ANNELID PROSTUMIUM. 257 



wick do not express a definite opinion on this point, but they 

 show most conelusively that in its development the preoral 

 segment resembles a true mctaniere. It has paired mesoblastic 

 somites, develojjed post-orally as the first of the series which 

 shift forwards in front of the moutli. As in the posterior 

 segments, each of these somites becomes hollowed out to form 

 the ccelom, from the wall of which is developed a rudimentary 

 "nephridium^^ (peritoneal funnel). '^ It presents exactly the 

 same relations as do the nephridia of posterior somites/^ says 

 Mr. Sedgwick (15), and adds, ''The first somite, therefore, 

 behaves exactly as do the posterior somites." 



As pointed out by Professors Korschelt and Heider, in their 

 excellent text-book of embryology (7), it can now hardly be 



. Tig. 5. 



m 



mar 



m 



Ventral view of an embryo of Peripatus capeusis (after Balfour). 

 Pr.l. Proceplialic lobe. m. Mouth. 



doubted that the antennae of Peripatus were primitively post- 

 oral, and that the segment to which they belong is therefore 



