OBSERVATIONS ON COLEOPTEKA. 



i8 7 



tion aid in this process, but that the rupture should occur so 

 regularly in the mid-dorsal line is remarkable, if this be the only 

 cause of the rupture. In the insects that I have examined there 

 always exists in the mid-dorsal line a special device to aid in the 

 splitting of the old cuticula at ecdysis. 



This apparatus in L. decimlineata consists of a well-marked 

 laterally flattened invagination extending caudalward from the 

 region of the occipital suture, where it extends deeply into the 

 head (Fig. 8). 



os. 



FIG. 9. L. decimlineata. Section through mesothorax. (A) and second ab- 

 dominal segment; (B) to show continuation of the modifications of median dorsal 

 line of body to permit of rupture at ecdysis. 



This line of weakness in the mid-dorsal line is also the last 

 point where the ectoderm closes in in development and is in dec- 

 imlineata turned inward to form a median dorsal fold from the 

 anterior edge of the occiput to the first abdominal segment and 

 in this median dorsal furrow the chitin is easily broken during 

 ecdysis. When the secondary cuticula represented in white in 



