i68 ZOOLOGY 



Those members of the armed Gephyrea whose developement 

 has been investigated show unmistakable affinities to the 

 Chaetopods. Their larvae exhibit a metameric segmentation, 

 but the somites disappear early. Traces of segmentation are 

 retained in the adult in a few cases, such as the four pairs of 

 nephridia in one species of Thalassema, the double ring of 

 setae in UcMurus Pallasii, and possibly in the rings of hooks 

 and circular nerves of many forms. A connecting link between 

 the Gephyrea armata and the Chaetopoda may exist in the 

 curious worm SterTiaspis. This animal, usually classed with 

 the Chaetopoda, retains a well-marked segmentation ; and its 

 blood-vessels, whUst resembling in their disposition the 

 more important vessels of the Gephyrea, open into a well- 

 developed system of capillaries. On the other hand the looped 

 intestine, one pair of brown tubes, retractile anterior end of its 

 body, and — in Sternaspis spinosa — a long bifid prostomium, de- 

 scribed by Sluiter, are all features shared in common with the 

 Gephyrea. 



The unarmed Gephyrea have an abbreviated developement 

 which shows no traces of metameric segmentation, but this 

 hardly seems a sufficiently important difference to warrant the 

 breaking up of the group. 



