678 



TEXT-BOOK OF ENTOMOLOGY 



It should be borne in mind that the process of development of the 

 head of the highly-modified Muscidse is much more complex than in 

 the more primitive Diptera. 



In their essay on the development of the head of the imago of 

 Chironomus, Miall and Hammond arrange the dipterous types 

 thus far examined, in the order of complexity of the imaginations 

 which give rise to the head of the imago, in the following order : 



1. Culex. Relatively simple. Invaginations of the imaginal buds, 

 shallow. 



2. Corethra, Simulium. ) T 



~, . ^ Intermediate. 



3. Chironomus, Ceratopogon. J 



4. Muscidae. Relatively complex. Invaginations deep, and appar- 

 ently, but not really, unconnected with the epidermis. 



b. Development of the internal organs of the imago 



It has already been observed that most of 

 the organs of muscid larvae (and this applies 



st to most Diptera, Lepidoptera, Coleoptera, and 



~.i. Hymenoptera) are destroyed through the 

 action of leucocytes, and that their reforma- 

 tion is accomplished by definite groups of 

 embryonal cells, the imaginal buds or folds. 

 Destruction and rebuilding occur during the 

 pupa stage in such a way that in many cases 

 while this process is going on the continuity 

 of the organs does not seem to be disturbed. 

 These transformations especially concern the 

 hypodermis, the digestive canal, the muscles, 

 the fat body, and the salivary glands. 



The transformation of the tracheal system 

 is only partial, being in part a simple pro- 

 cess of regeneration through cell-division. 

 Slighter changes affect the heart, the central 

 nervous system, and the reproductive system 

 (Fig. 630). 



The hypodermis. The hypodermis of the 

 imago arises through an extension of the 

 ectodermal part of the imaginal buds. \\V 

 have already mentioned this for the thorax. 

 As the appendages of the thorax in the pupa 

 gradually attain perfection, the hypodermis 



FIG. two. Median longitu- 

 dinal section through larva of 

 blow-fly during the process of 

 histolysis : an, antenna ; be- 

 tween an and w, rudiments of 

 eye ; w, wings ; h, halteres ; 

 Z>j-&., legs ; /, fat-body ; d, 

 middle of intestine ; n, gan- 

 glia ; at, stigma ; 6, 7, 6th and 

 7th body - segments. After 

 Graber, from Sharp. 



