No. 3-] THE PHARYNX OF ALLOLOBOPHORA. 107 



with the figures of Hcscheler in regard to the extent of the 

 cuticle on the dorsal wall of the pharynx, they contained also 

 some alternating patches of what seemed to be cuticle and of 

 ciliated areas on the ventral wall and at points in the 

 digestive tract even further back than the regenerated 

 pharynx itself. 



For this reason I have attempted to get more certain results 

 by the use of the following experimental methods. Worms, 

 from which the seven anterior segments had been removed, so 

 that no part whatever of the old pharynx was left behind, were 

 allowed to regenerate for a period of between twelve and 

 eighteen days. As a rule the fusion of the ectodermal invagi- 

 nation with the pharynx occurs about fifteen days after the 

 removal of the anterior end of the worm, --although there is 

 considerable individual variation in regard to this point, and 

 also some difference due probably to the temperature, etc. At 

 the end of this time the anterior tip of the new part of the 

 worm was removed in one of two ways : either it was burned 

 off by touching it with a hot needle, or it was cut off with fine 

 scissors. The latter method, though more difficult to carry 

 out successfully, proved to be the better one because the piece 

 cut off could be preserved to show whether the pharynx had 

 joined the ectoderm at the time of the second operation. The 

 worms were once more allowed to regenerate and were finally 

 killed between ten and fifteen days after the second operation. 

 In all cases the worms survived both operations and showed a 

 perfectly normal regeneration, the only point of difference from 

 worms that had undergone only the first operation being that 

 the new pharynx had time to regenerate before the second 

 ectodermal invagination had fused with its anterior end. The 

 object of the experiment was to determine whether a normal 

 pharynx would develop from the endoderm if the fusion of the 

 ectoderm with it was prevented for a sufficient length of time 

 to allow this development to take place. 



It is difficult to determine on the living object whether or 

 not the ectodermal invagination has met the endoderm, and 

 since for my purposes it was best to wait as long as possible 

 before the second operation, it happened in two or three cases, 



