ANNELIDES. 



13 



interior of which lies coiled up a long filament, which 



is often serrated at the end. Even a 



very slight pressure causes this thread 



to spring out, and these little darts, 



which are present in immense numbers 



in the skin of Hydrozoa (jelly-fish, etc.), 



serve both as weapons of defence and 



also to wound the small animals on 



which they feed. 



nz represents a nerve-cell, and it will 

 be seen that the hair in which it ter- 

 minates does not materially differ from 

 the rest. 



In the Annelides, also, the general 

 surface of the integument (Fig. 15) 

 presents tactile setae or cilise, which are scatteredipver 



Fig. 14.— Diagram of 

 part of the skin of 

 a sea-anemone (Ac- 

 tinia); after Korot- 

 nelf. dz. Glandular 

 cell ; nz, nervous 

 cell. 



Fig. 1 5.— Anterior part of body of nohemilla cnmata fafter Vejdovsky •). lb. Tactile 

 hair ; hp, hypoderm ; c, cuticle ; b, anterior part of brain ; a, eye ; ne, nerve- 

 fibrils ; y, anterior blood-vessel. 



tlie surface, and especially on the head. In some cases 

 * " Syst. und Morph. der Oligochoeten." 1884. 



