43 2 GEPHYREA 



continued into a long cilium which hangs down into the lumen 

 of the canal, and by its movement produces a nickering motion. 

 Beyond the free end of the large cilium the canal is lined with 

 ciliated cells. The remarkable resemblance this form of excretory 

 organ presents to that of the Platyhelminthes (vide p. 25) and 

 of certain Chaetopods is worthy of attention. In the young 

 Priapuloidea the duct with its branching canals is not masked 

 by the generative organs, but as the animals become mature, 

 diverticula from the duct arise, and the cells covering these become 

 modified into ova in the female, and into spermatozoa in the 

 male. The presence of these follicles masks the excretory part 

 of the gland. The ova and spermatozoa escape through the 

 ciliated ducts which open to the exterior one on each side of the 

 anus, and, contrary to what is the case with other Gephyrea, 

 leave the body without having ever been in the body-cavity. 



Nothing is known of the embryology of either member of this 

 family, but both genera appear to be sexually mature from the 

 end of May until October. 



Classification. The two genera which make up the Order 

 Priapuloidea are characterised as follows: 



Priapulus. The body is continued into one or two caudal 

 appendages, beset with hollow papillae ; these are ventral to the 

 anus. The introvert forms ^ to ^ of the total body-length ; it 

 is covered with spines in conspicuous longitudinal rows, the rest 

 of the body being ringed. The retractor muscles are numerous, 

 and are attached to the body -wall, some anteriorly and some 

 posteriorly. 



The genus includes the following five species : 



P. caudatus Lam. (Fig. 2 1 8). Hab. Coasts of Greenland, Norway, Great Britain, 



the North Sea, and the Baltic. 

 P. bicaudatus Dan. Hab. North Sea and Arctic Ocean. 

 P. glandifer Ehlers. Hab. Coast of Greenland, North Sea. 

 P. brevicaudatus Ehlers. Hab. North Sea and Baltic, from ten fathoms. 

 P. tuberculato-spinosus Baird. Hab. Falkland Islands. 



Halicryptus. No caudal appendages. Introvert ^ to ^ of 

 the total body length, with numerous spines arranged in close 

 circles. Eetractors numerous and all attached to the body- wall 

 anteriorly. 



H. spinulosus v. Sieb. (Fig. 219). Hab. North Sea, Arctic Ocean, and Baltic, 

 in from two to fifty fathoms. 



