OF ANNELIDS. 



233 



been studied, the eggs are probably laid in masses between 

 tide-marks, and the young, when hatched, swim freely on 

 the surface of the sea. The eggs of other worms are carried 

 about in lateral pouches. The germ undergoes a cleavage 

 phase and a gastrula stage. We have observed, in Salem 

 harbor, the development of Poly dor a (probably P. ciliatum 

 Clap.) which maybe found in August, in all stages, on the 



Fig. 153. A, earliest observed stage of Polydora,; B, Cephalula stage ; C'and D, 

 later stages. Author del. 



surface of the water. When first observed (Fig. 153, A ) the 

 body was spherical, with a short, broad intestine, and two 

 sets of large locomotive bristles. It then passed into the 

 cephalula state, the head clearly indicated and forming a 

 large hood. This stage is seen at B, which represents the 

 under side of the cephalula, the mouth being situated be- 

 tween the two large ciliated flaps (like the velum of larval 

 mollusks) of the hood ; the body is now segmented, with a 

 third set of bristles and a band of cilia on the penultimate 

 segment ; afterwards as at C, dorsal view, additional rings 

 are present ; the eyes are distinguishable, and there are two 

 more sets of bristles. The new segments are, as usual in all 



