4 IG F. H. Krecker, 



parts. The ectoderm conveys the impression of its being desolved 

 although no degeneration could be observed. In the meantime a 

 slight depression occurs in the ectoderm and as it becomes deeper 

 the ectodermal cells pass to one side or the other to form the walls 

 of the invagination, which is the proctodaeum, until finally the central 

 portion of the depression is deprived of cells and the ojjening is com- 

 pleted. 



In the course of inspecting individuals from which the intestine 

 had been removed a few were noticed which seemed to have either a 

 bifid posterior end or eise to have an anal opening some distance from 

 the posterior end of the body in which case one was lacking where it 

 should normally appear. One individual in this condition was noted 

 in which the new growth started at a point about one segment anterior 

 to the posterior end of the body and extended quite an appreciable 

 distance froin the body. The intestine had been cut off one segment from 

 the end of the body and evidently for some reason it had grown over to 

 the side. At this point an opening had then formed. The worm was 

 kept a while longer biit unfortunately it died before it was again exa- 

 mined so that the cause of this abnormal growth could not be deter- 

 mined. Later a somewhat similar case was observed, the growth had 

 progressed a very short distance and the worm was therefore killed 

 in the hope of determining what had caused it. Upon examination 

 of sections it was found that an anal opening was in process of for- 

 mation. The intestine stopped about a segment from the end of the 

 body and at its posterior end where regeneration usually occurs there 

 was only the slightest indication of an outgrowth. At a point very 

 slightly anterior to this it had grcwn out laterally and extended over 

 to the body wall meeting it about midway between the dorsal and 

 the ventral surfaces. At the point of contact a fusion between the 

 intestine and the ectoderm had occured and a slight invagination of 

 the latter had also taken place preparatory to the formation of a procto- 

 daeum. An opening had not yet been established but the ectoderm 

 directly opposite the intestine was thin and its cells in process of mi- 

 gration exactly as in the formation of an opening at the posterior end 

 of the body. The adjacent portions of the ectoderm on both sides of 

 the thin area were protruded so as to form two Ups, the cells of which 

 were dividing both mitotically and amitotically. Some cells were 

 enlarged, particularly on the ventral posterior side where in addition 

 they were migrating into the coelom (Fig. 21). 



In spite of the fact that the growth had not progressed far the 



