258 C. M. Child. 



and under ordinary conditions the width of the body is uniform 

 to about the level of the eyes; during the changes in proportion 

 accompanying regulation the decrease in width may begin a con- 

 siderable distance anterior to the eyes, hence the importance of 

 giving this measurement. The following column "Greatest 

 width" gives the width of this widest anterior region. The tenth 

 and eleventh columns also require a word of explanation. The 

 cut surface contracts after section in all cases and thus the extreme 

 posterior end of the old tissue is more or less reduced in width. 

 When the new tissue arises its width is the same as that of the con- 

 tracted cut surface, hence the arc of the cut surface is equal to the 

 width of the new tissue at its anterior end, the eleventh column 

 of the table. It is desirable, however, to determine not only the 

 width at this point, /. e.y the arc of the contracted cut surface, but 

 also the width of the body just anterior to the region where it is 

 effected by the local contraction. These measurements are given 

 in the tenth column under the heading, "Width at posterior end 

 of old tissue." In Fig. 2 the difference in level of the two measure- 

 ments is indicated by the transverse dotted lines. As is evident 

 from the figure the "width at the posterior end of the old tissue" 

 is measured on the tangent to the contracted cut surface at right 

 angles to the longitudinal axis and the width at the anterior end 

 of the new tissue is the arc of the cut surface. As in Fig. 2, there 

 is usually a marked difference between these two measurements 

 except in later stages and this difference represents the contraction 

 of the cut surface. 



The last column of the table gives the number of the figure 

 representing each stage, in order that comparison between the 

 table and the figures may be readily made. 



The intervals are not exactly the same for Series 27 as for the 

 other series, but the difference is not sufficiently great to prevent 

 comparison. A few data are given to supplement the figures and 

 table. 



Series ZJ {Figs. i~6). The level of section 4 mm. from the 

 anterior end is indicated in Fig. i. The short anterior piece 

 resulting from section contains nothing but the head region and a 

 short portion posterior to the ganglia. The margins of this part 

 of the body are used chiefly for drawing the body forward and for 

 the flying movements, not, like the posterior end, for holding to 

 the substratum during locomotion. As a matter of fact this piece 



