198 MANUAL OF ZOOLOGY SECT. 



the exterior, in the case of the sperms probably through the 

 nephridia ; in the case of the ova, which are much too large 

 to pass out in this way, probably through apertures tempo- 

 rarily formed by rupture of the body- wall ; and impregnation 

 takes place by contact between the two sets of elements 

 while floating freely in the sea-water. 



FIG. 113. Serpulae with their tubes. (After Quatrefages.) 



Other annelides which may be collected along with Nereis 

 on the sea-shore will be found to resemble it in the seg- 

 mented character of the body, and the presence of para- 

 podia with setae, but to differ from it in the general shape, 

 the number of the segments, the form of the parapodia, and 

 the arrangement and shape of the setae, the form of the 

 head with its eyes and tentacles, and other points. Many 



