408 T. H. MOKGAN. 



The modificatious may be classified under the followiug 

 categories : 



A. Part of a metamere compressed. 



B. Failure of external septal lines to meet. 



C. Spirals in front of the 15th metamere. 



D. Spiral involving the 15th metamere. 



E. Results of the introduction of compound metameres. 



A. Plate 41, figs. 1—3. 



In fig. 1, A B, the 4th metamere is not fully developed on 

 the right side of the body. The ring is narrower, and has less 

 pigment on the right side. The vasa deferentia open on the 

 16th metamere, as shown in b. 



Fig. 3, A B, shows another worm with the 2nd metamere 

 similarly modified. The vasa deferentia open on the 15th 

 metamere. 



Fig. 3, A B, shows the 5th metamere reduced on the left 

 side. The vasa deferentia open on the 16th metamere. 



Conclusion. — It is not a little surprising to find in two of 

 the three cases where an anterior metamere is partially unde- 

 veloped, that the openings of the vasa deferentia have shifted 

 one segment posteriorly. The data are too small to lead to any 

 definite conclusion. 



B. Plate 41, figs. 4—11. 



In fig. 4 we see that the line of division between the 9th and 

 10th metameres failed to meet exactly on the upper surface. 

 The vasa deferentia opened normally, if we count the 9th and 

 10th as true metameres. 



In fig. 5 the line between the 5th and 6th metameres failed 

 to meet above. Vasa deferentia normal. 



In fig. 6 the line between the 4th and 5th metameres failed 

 to meet. Vasa deferentia normal. 



In fig. 7 the line between the 3rd and 4th metameres failed 

 to meet. Vasa deferentia normal. 



In fig. 8 the line between the 13th and 14th metameres 

 failed to meet. 



In fig. 9 the line between the I2th and 13th, and in fig. 10 



