SENSE-ORGANS OF CAPITELLIDjE 163 



These sense - organs were closely compared by 

 Eisig with the lateral line sense-organs of aquatic 

 vertebrates (fishes and batrachians), the function 

 of which is partly equilibrating and partly the 

 perception of currents and wave - movements. 

 The most remarkable histological resemblance is 

 manifested between the lateral sense-organs of 

 the Capitellidae and the lateral line sense-organs 

 of Vertebrates. In both cases the essential organs 

 consist of small, solid, roundish, epidermal buds, 

 from which fine stiff sense - hairs project freely 

 into the surrounding medium ; and the resem- 

 blance is further enhanced by their segmental 

 arrangement. The correspondence could hardly 

 be greater, the convergence could hardly be 

 closer, the homology could not be more remote 

 than infinity. 



Within the limits of the order of Polychseta, 

 Eisig has established the true homology between 

 the lateral sense-organs of Capitellidse and the 

 dorsal cirri of neural parapodia such as occur in 

 the family Glyceridae. Through this family it is 

 made clear that the lateral organs are homologous 

 with the dorsal cirri of Polychseta as a whole. 



Most morphological arguments work both ways, 

 and it is not surprising that after having estab- 

 lished the homology between the endostyle of 

 Amphioxus and the Ascidians and the thyroid 

 gland of Ammocoetes, the larval form of the 



