248 MORGAN. [Vol. VII. 



appeared, leaving 38 in all. Of these only 2 were completely 

 normal, or the proportion of abnormal to normal was as 38 to 2 

 or 19 to I. For this reason, I think we are enabled to account 

 for the greater number of abnormalities in complete (adult) 

 worms than in the newly hatched embryos. 



Lastly, an attempt was made to find an interpretation of the 

 spiral and split-metameres. To do this the anterior region of 

 the worms was studied where one may be guided by definite 

 landmarks. To take a single example : It is known that the 

 external openings of the vasa deferentia occur on the 15th meta- 

 mere. Now, if split segments can be found anterior to or 

 including the 1 5th metamere, we are furnished with a clue to 

 their interpretation. Such abnormalities are to be found, but 

 are not very common, and a very large number of individuals 

 had to be examined in order to obtain sufficient material to 

 reach a safe conclusion. 



At the very outset, however, I met a disturbing factor. It 

 had to be first determined whether the openings of the vasa 

 deferentia always appeared on the 15th metamere. Such is not 

 the case. Thus, in 799 worms, 20 were found in which this 

 was not true. That is to say, 20 worms showed abnormalities 

 as to the position of the external openings of the vasa deferentia. 

 The following table indicates the position of the external open- 

 ings of the vasa deferentia in 1 2 of the 20 cases : — 



I ex. vas d. occurred on loth metamere. 



1 « " nth " 



2 " " 1 2th " 

 4 « « 14th " 



Normal. 

 4 « « 1 6th " 



In cases in which the external vas deferentia were found on 

 segments anterior to the 15th, this maybe explained in some 

 cases as due to injury or loss of the anterior metameres,i but I 

 believe that this does not account for all such cases. These 

 results show at least that care must be taken in utilizing the 

 15th segment as a fixed point. In all cases due weight has 

 been given to this factor. 



In this same lot of 799 worms there were 32 cases (after 

 removing the 20 above) in which abnormalities (splits, spirals, 

 1 I am collecting experimental evidence on this point at present. 



