650 C. B. HARDENBERG. 



except that group 7 now consists of two setae. Abd. 8 is as 

 in second instar. Abd. 9 also as in second instar, with the 

 addition of a rudimentary seta in front of the single one 

 representing group 7. Abd. 10 iio change except a heavier 

 chitinisation. Anal legs with 10 to 17 booklets. 



Over the entii'e body of the larva a great change has 

 occurred in the composition of the skin. While during the 

 first two instars the skin appeared as a structureless membrane, 

 we find this now strengthened and toughened by numerous 

 minute granular plates (text-fig. 2, d). These are somewhat 

 more prominent on the cephalic edges of the segments, and 

 laecome especially developed at the front edge of the anal 

 segment, where they form a strong band across the dorsal 

 and ventral aspect. Between and posterior to the anal legs 

 the skin is armed with numerous finely pointed teeth directed 

 towards the base of the leg. They are arranged roughly in 

 parallel bands surrounding the medial and caudal part of the 

 leg-plate, and gradually become smaller, and merge into the 

 chitinous tuberosities of the surrounding skin. 



This structure of the skin becomes more and more pro- 

 nounced with succeeding instars, and reaches its greatest 

 development in the ante-penultimate instar (text-fig. 2, f). In 

 the last stage the amount of chitinisation of the skin is 

 considerably reduced. 



Fourth Instar. 



Length of larva 21 mm. at end of instar, width 6 mm., the 

 place of greatest width at middle of third abdominal segment, 

 (xeneral colour of body sorghum brown (XXXIX) ; on first two 

 abdominal segments Hay's brown (XXIX). Ground colour of 

 thoracic shield inaize yellow (IV), ground colour of head 

 auburn (II), markings ou head, thorax, thoracic plates and 

 legs, plates on first abdominal segment, anal plates and legs, 

 seal brown (XXIX), plates on other segments and abdominal 

 legs Hay's brown (XXIX). 



Head. — Width of head-case 8 mm. Adfrontals now dis- 

 tinctly separated from parietals, broad, reaching to two-thirds 



