ONYCHOPHORA 



319 



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 haemocoelic but the embryonic coelom 

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

 gastrula stage the blastopore becomes elongated, the anterior part 



']m V !\§jf,a 



D 



pr.s 



Fig. 216. A, Transverse section through Peripatus. e.g. crural gland; e.m. 

 circular muscles ; d.l.m. dorsal longitudinal muscles ; g. genital organ ; h. heart ; 

 ha. haemocoele; int. intestine containing^, peritrophic membrane; n. excre- 

 tory tubule; n.c. nerve cord; ob.m. oblique muscles; pf. pericardial floor; s.g. 

 slime gland; s.l.g. salivary gland; v.l.ni. ventral longitudinal muscle. B, An 

 excretory organ of Peripatus. bl. bladder ; c.d. ciliated part of duct ; d. duct ; 

 e.s. coelomic sac ; ex. external aperture. 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 Manton; C, after Moseley ; D, after Balfour. 



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

 part closes (Fig. 216). 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 

 this is formed, and eventually becomes part of the segmental excretory 



