LARVAE OF ANNELIDS. 



213 



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 Polydora (probably P. ciliatum 

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



Pig. 147 A, earliest observed stage of Polydord- J9, Cephalula stage ; Pand D, 

 later stages. Author del. 



surface of the water. When first observed (Fig. 147, 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 



