505 



tissues occur during the pupal period. On the fourth day of 

 pupal life the integument chitinises and the imago is seen 

 lying within the transparent pupal sheath. 



The development of the head from the first two segments 

 is fully described. The head appears to be composed of five 

 primitive segments. The mouth appendages develop by the 

 evagination of imacfinal discs. The latter are seen in the first 

 larval instar as thickenings of the integument, consisting of 

 minute embryonic cells. These, like the appendages of the 

 legs, wings, and abdomen (in females) become invaginated 

 during larval life as the surrounding larval cells increase in 

 size, and only evaginate again at metamorphosis. These, and 

 all other imaginal tissues, are to be observed in the larvae at 

 all stages of their development. The most noteworthy feature 

 in the mouth appendages is the occurrence of a mandibular 

 palp. In the antennae, organs of smell, touch, and hearing 

 are described. 



The compound "thorax" is described as consisting of 

 three thoracic segments, as well as the first abdominal and 

 dorsal part of the second abdominal. The lower part of the 

 second remains as the petiole. This is contrary to accepted 

 views. Legs and v/ings are formed as outgrowths from 

 invaCTi*nated discs on the ventral side of the thoracic segments. 



The ovipositor is formed by the outgrowth of three pairs 

 of imaginal discs on the twelfth, thirteenth, and fourteenth 

 segments ; they come into intimate relation and co-operate to 

 form the complex ovipositor. 



The penis is formed as a remarkable modification, accom- 

 panied by partial invaginations, of the hinder abdominal 

 segments. 



B. HisfoJofiical Changes ifi Integument . 



The larval cells, having grown greatly in size during the 

 feeding period, disint-egrate ; in part they dissolve in the 

 blood: in part they are removed by leucocytes. The minute 

 imaginal cells develop at their expense and no break in the 

 integument is ever to be seen. Tlie underlying somatopleure 

 also metamorphoses. 



Bristles are formed as partial chitinisations of cells or 

 groups of cells wdiich have grown out into the form of bristles. 

 Pubescences are formed as chitinisations of the frayed exteriors 

 of other cells. Phragmas are formed as cleft-like invaginations 

 of the integument ; false phragmas by the dovvmgrowth of the 

 margin of segments. 



The eye is represented in the first intsar by an integu- 

 mental thickening consisting of three layers of cells. From 

 the outer develop the lens, and vitreous cells ; from the middle 

 p 



