8 bulletin: museum of compaPwAtiye zoology. 



The mouth opens on the ventral surface, and a dorsal and ventral pair 

 of " teeth " have made their appearance in the oesophagus (see Figure 

 20). The worms are now about 0.8 mm. in length. Internal as 

 well as external evidences of segmentation now appear (see Figure 8, 

 Plate 1) and the dissepiments (ds) are complete. The walls of the 

 mid gut are very thick and consist of large, irregularly shaped, highly 

 vacuolated cells containing a number of yolk spheres. The cells of 

 the oesophagus (oes) are of an epithelial character. The peripheral 

 circular muscles and the deeper lying longitudinal muscle strands are 

 beginning to appear, aud the ventral nerve chain («) is very apparent- 

 In fact, the animal is no longer a larva, but is a young worm. 



Figures 21-23, 25-27, illusti'ate the condition of the worm at the 

 end of the 26th day. There are now five pairs of parapodia, and the 

 dorsal aud ventral cirri of the posterior segment have become long and 

 prominent (see Figure 23). The dorsal and ventral jaws of the oesoph- 

 agus are shown in the side view of the head given in Figure 22. 

 Figures 26 and 27 are views from above and from the side, respectively, 

 of the dorsal pair of jaws. The condition of the ventral pair of jaws 

 is still quite similar to that in the 16-day -old worm shown in Figure 

 20. The worms are now 1.2 mm. long. They burrow readily 

 beneath the surface of sand, but never swim through the water. 



Figure 24 shows the condition of a worm 34 days old. The animal 

 is now 1.5 mm. in length, and there are still only five pairs of para- 

 podia. The mature coloration is beginning to appear in two reddish- 

 colored spots immediately back of the eyes. I did not succeed in 

 rearing any worms beyond this condition, and know nothing of the 

 mode of formation of the prsestomium and cephalic cirri of the adult 

 worm. It will be observed that in the young worm the mouth opens 

 on the ventral surface and the praistomium is supra-oral, Avhile in the 

 adult worm the pi-testomium and cephalic cirri are sub-oral (compare 

 Figures 3 aud 22). 



General Conclusions. 



Remarkably little has been written concerning tlie egg-laying habits 

 of Polychretae. Wilson ('92, p. 371) states that the eggs of Nereis 

 limbata and N. megalops are discharged at night while the animals 

 are swimming upon tlie surface of the water. The egg-laying season 

 extends at least from Juue until September. "The animals appear in 

 abundance only on warm still nights, and even then are rarely found 



