(74) 

 514 0. GORDON HEWITT. 



are repeated fairly regularly from segments (by segments I 

 ,mean body-segments) four to twelve and a detailed descrip- 

 tion of the muscles of one of these segments will serve for the 

 rest. The muscles,, though continuous in most cases from seg- 

 ment to segment, are attached to the body- wall at the junction 

 of the segments. The most prominent muscles are the dorso- 

 lateral oblique recti muscles. In segments six to twelve there 

 are four pairs each of external (ex. d. L), and internal dorso- 

 lateral oblique recti (in. d. I.) muscles ; in segments four and 

 five there are five pairs of external and six pairs of internal 

 dorso-lateral oblique muscles. Ventral to these muscles are 

 four pairs of longitudinal ventro-lateral muscles (L v. L) ; the 

 muscle bands of the two more ventral pairs are double the 

 width of those of the two more lateral pairs. In the fifth seg- 

 ment there is only one of the more lateral pairs of the longi- 

 tudinal ventro-lateral muscles present, and in the fourth 

 segment only the two more ventral pairs remain. In addition 

 to these muscles there are two other pairs of oblique recti 

 muscles ; these are, a pair of ventro-lateral oblique muscles 

 (v. L o.) and a pair of internal lateral oblique muscles (i. I. o.) ; 

 both of these are absent in the segments anterior to the sixth. 

 The foregoing muscles, namely the dorso-lateral oblique, the 

 internal lateral oblique, the ventro-lateral oblique and the 

 longitudinal ventro-lateral, by their contraction, bring together 

 the intersegmental rings and so contract the body of the larva. 

 Attached externally to the anterior ends of the longitudinal 

 ventro-lateral muscles are a number of pairs of ventral oblique 

 muscles (v. o.) ; they vary in number from two to eight pairs in 

 each segment. The number increases posteriorly from two 

 pairs in segment four to four pairs in segment five, five pairs 

 in segment seven, seven pairs in segment ten, eight pairs in 

 segment eleven; the number of pairs then decreases to six or 

 seven pairs in segment twelve. The more ventral pairs of 

 these muscles are not attached at their posterior ends to the 

 intersegmental ring but to the ventral wall of the segment 

 and no doubt assist in bringing forward the ventral spiniferous 

 pads. In segments four to twelve there are three pairs of 



