THE HEAD-APPENDAGES 



549 



The post-oral appendages of the head are the mandibles and the 

 1st and 2d maxillae, besides the supposed premandibular segment 

 already referred to on pp. 50-54, which only temporarily exists. 



The trophi or oral appendages are all alike at first, but soon differ 

 in shape, acquiring their characteristic form shortly before the 

 embryo leaves the egg. The mandibles of (Ecanthus are said by 

 Ayers at the time of revolution of the embryo to be slightly bilobed, 

 and in his Fig. 5, PL 19, they are represented as deeply trilobed, 

 but in general they are undivided. The 1st maxillae are at this 



be*-- at 



FIG. 528. Two embryonic stages of the primitive streak of Melolontha. A, younger stage, 

 with rudiments of eight pairs of abdominal appendages (a l -a 8 ). J3, older stage, the primitive band 

 now very broad : a, 1st abdominal appendage, in E sac-like; *, place of adhesive disc ; g, brain ; 

 1. clypeo-labrum ; H, lateral cord of the ventral nervous cord ; other lettering as in previous figures. 

 After Graber, from Korschelt and Heider. 



time distinctly trilobed. The 2d maxillae are separate, and dis- 

 tinctly though unequally bilobed, becoming united shortly before 

 birth. In the embryos of dragon-flies they are at an early date 

 very large and long, and directed backwards, and are not fused 

 together until just before hatching, when the extraordinary mask- 

 shaped labium is fully developed. 



The distal parts of the labium, such as the ligula, palpifer, and 

 palpus are elaborated before the mentum and submentum. Many 

 details as to the final changes in the mouth-parts before hatching 

 remain to be worked out. 



