No. 3.] THE PHARYNX OF ALLOLOBOPHORA. 



15. The tip of the regenerated part was destroyed with 

 a hot needle on February 2, and the worm was killed on 

 February 17. 



Both figures show the diverticulum which has grown out 

 from the walls of the oesophagus about to open to the exterior 

 by fusion with the ectodermal pit ; and a comparison with the 

 sections in the same neighborhood shows that these two repre- 

 sent the nearest approach of ectoderm and endoderm to be 

 found in the two specimens. The walls of the pharynx and 

 its musculature, especially 

 on the dorsal side, are 

 well developed. In both 

 worms a nerve cord and 

 a cerebral ganglion have 

 been formed, the latter 

 for the second time. 

 Owing: to the slight ob- 



o o 



liqueness of the section, as 

 shown in Fig. 2, the nerve 

 cord is cut for only a part 

 of its length. The muscles 

 of the body wall have be- 

 gun to differentiate and 

 there are clear indications 

 of metamerism. All of the 

 worms used in this set of experiments, as well as all those in a 

 later set made to test these results, present a similar condition 

 of things. 



From these results we must conclude that the lining of the 

 pharynx is regenerated from the endoderm, while the new ecto- 

 derm turns in for a very short distance to meet the pharynx 

 and form the mouth. 



The objection may be raised that the possibility of a later 

 pushing in of the ectoderm to form the ultimate lining of the 

 pharynx is in no way removed. But there is no evidence for 

 such an occurrence and, even if it did take place, the fact 

 remains that the musculature of the pharynx develops around 

 an endodermal tube, as my experiments have shown, while in 



FIG. 2. 



