A STUDY OF METAMEEISM. 401 



for the variations — abnormalities — to be present^ and the worm 

 still be able to reach sexual maturity. In another worm con- 

 taining many abnormalities there were 131 half-metameres on 

 the right side of the body and 139 on the left side. In all 

 there were seventy-nine normal rings. The number of half- 

 rings in these worms is noticeably very large as compared with 

 the normal number. It should also be noticed that the 

 abnormalities are not confined to any one part of the body, 

 but scattered throughout the whole length of the worm. 



We may now study the relative proportion in which 

 the diflFerent modifications, described above, are found. In a 

 lot of 318 worms 218 were found to be normal externally with 

 respect to the metameres, and 100 abnormal. This is in the 

 proportion of 1 to 2'18, or in general one worm of every three 

 was abnormal. 



In the same worm there often occurred more than a single 

 abnormality. Thus in the above 100 — 



With . . 1 abnormality . . .65 



,, . .2 abnormalities . . .16 



„ . . 3 „ . . .10 



,, more than 3 ,, ... 9 



100 



An examination of the material shows that there is practi- 

 cally no difference in the number of compound metameres on 

 the right as compared with the left side of the body. 



The examination shows, however, that a much larger 

 number of " splits " are present on the dorsal surface of the 

 body than on the ventral surface. In a compound metamere 

 we have a split above for one below, but in such spirals as 

 shown in figs, viii, x, &c., we have two above and none below, 

 and such spirals have their " splits " on the dorsal surface in 

 the greater number of cases. I regard this as important, as it 

 gives a clue to the solution of the problem. 



An examination of the material shows that there are thirty- 

 two cases of spirals beginning and ending above (category viii), 

 and only one case of a spiral beginning and ending below. 



