EMBRYONIC GROWTH OF THE WINGS 



1-29 



cavity. It is a continuous membrane formed of plasma which I will call 

 the ground membrane of the epithelium. Through this ground mem- 

 brane pass blood-corpuscles as well as blood-lymph." (Schaeffer.) 



br 



FIG. 141. Anterior part of young larva of Simulium sericea, showing the thoracic imaginal 

 buds: p, prothoracic bud (only one not embryonic) ; to, 10', fore and hind wing-buds ; I, I', I", leg- 

 buds; n, nervous system; br, brain; e, eye; ad, salivary duct; p, prothoracic foot. After 

 Weismann. 



Afterwards (1866) Weismann studied the development of the 

 wings in Corethra plumicornis, which is a much more primitive and 

 generalized form than Musca, and in which the process of develop- 

 ment of the wings is much simpler, and, as since discovered, more as 

 in other holometabolous insects. He also examined those of Simu- 

 lium (Fig. 141). 



In Corethra, after the fourth and last larval moulting, there arises at first by 

 evagination and afterwards by invagination a cup-shaped depression on each 

 side in the upper part of the mesothoracic segment within which the rudiment 

 of the wings lies like a plug. The wings without other change simply increase 

 in size until, in the transformation into the pupa by the withdrawal of the 

 hypodermis, the wings project out and become filled with blood, the tracheae 

 now being wholly wanting, and other tissues being sparingly present. 



FIG. 142. Section through thorax of a Tineid larva on sycamore, passing through the 1st pair 

 of wings (w) : ht, heart ; i, oesophagus ; , salivary gland ; tit, urinary tube ; no, nervous cord ; m, 

 rec'.i muscles ; a part of the fat body overlies the heart. A, right wing-germ enlarged. 



