ONYCHOPHORA 283 



papillae arising in the embryo and must without doubt be regarded 

 as appendages. 



The trunk appendages are short and conical, hollow, bearing at 

 their distal ends spinose pads and a retractile terminal "foot" with 

 two recurved claws. 



The adult body cavity is haemocoeHc but the embryonic coelom 

 is well developed. In the development of Peripatiis just after the 

 gastrula stage the blastopore becomes elongated, the anterior part 



ap.ex. 



Fig. 205. A, Transverse section through Pm/)af?/j eJwarrfw, adult ?. al. 

 alimentary canal (ciliated); ap.ex. aperture of excretory organs; h. heart; 

 m.l. longitudinal and m.c. circular and diagonal muscle layers ; n.c. nerve cord ; 

 ut. uterus. B, An excretory organ of P. edwardn. hi. bladder ; coe.s. coelomic 

 sac; nepr. nephrostome; sec.can. secretory canal. C, Part of the ventral and 

 lateral body wall of P. capensis to show irregular distribution of tracheae {tr.). 

 D, Ventral view of embryo of P. capensis to show six pairs of mesoblastic 

 somites, pr.s. primitive streak; and blastopore closed in the middle to form 

 mouth (M.) and anus {an.). A and B, after Gaffron; C, after Moseley; 

 D, after Balfour. 



giving rise to the mouth, the posterior to the anus, while the median 

 part closes (Fig. 205). Behind the blastopore is a primitive streak 

 which forms the paired mesoblastic somites. The anterior pair move 

 in front of the mouth and help to provide the mesoderm of the 

 tentacular segment. None of the rest become preoral. In all seg- 

 ments the somites early acquire a cavity, the coelom, and later divide 

 into two. Of these the ventral part migrates into the appendage as 



