404 T. H. MORGAN. 



In those cases iu wliich the openings of the vasa deferentia 

 occur on a segment anterior to the 15th metaraere, we may 

 be dealing with a case of incomplete regeneration of the ante- 

 rior metameres. In fact, in the first case given there was 

 evidence for believing that the anterior end had just regene- 

 rated, and even the second case gave slight evidence of the 

 same thing. That all of the cases can be explained in this 

 way is, I think, highly improbable. We find, as the table 

 shows, the greatest variation on each side of the 15tli meta- 

 mere, pointing in favour of individual egg variation rather 

 than regeneration. This view is also strongly supported by 

 an examination of the internal conditions. Again, those cases 

 recorded above in c and d show conclusively that the openings 

 of the vasa deferentia may shift, and in these cases regenera- 

 tion is largely out of the question. 



In order, however, to satisfy myself completely, i.e. experi- 

 mentally, on this point, I tried by (artificially) cutting off" the 

 anterior metameres of a large number of worms to determine 

 what proportion of these regenerated the full number of 

 anterior metameres. The results are given in a later section. 



B. There were six cases out of the twenty in which the 

 openings of the vasa deferentia were in diff'erent metameres of 

 the same worm. These are figured in PI. 42, figs. 48 — 58. 



In the first case, fig. 48, the 15th metamere has on its right 

 side (left of figure seen from below) an opening of the vas 

 deferens. The left side of the 15th has no opening, but on 

 the 16th metamere of that side occurs the opening of the left 

 vas deferens. One such case is recorded. 



In fig. 49 another variation is found. Here the 15th meta- 

 mere has on the left side of the body its proper opening, but 

 there is no opening on the right side of that segment. On 

 the 16th metamere, however, and on the right side, the right 

 vas deferens opens. Four such cases are recorded. 



In fig. 50 we find that the right side of the 15th metamere 

 has an opening, but not the left side. On the 14th metamere 

 we find the opening of the left vas deferens. One such case is 

 recorded. 



