142 



PRINCIPLES OF EMBRYOLOGY 



for the gene aristopedia. This causes part of the antennal bud to develop 

 into a leg instead of an antenna; and it was found that the amount of the 

 bud which is diverted into this abnormal channel of differentiation can be 

 altered by the temperature to which it is subjected during the third larval 

 instar. One must conclude that the determination of the imaginal char- 

 acter is still very labile until at least the time of pupation. Shatoury (1955) 



A 



^ 



Figure 8.14 



The female genital bud of Drosophila: a shows the genital organs of the 

 adult; Ov, oviduct, at the top the two branches which continue to the 

 ovaries have been cut through; R.S. receptaculum seminalis; Spt., sperma- 

 theca; Ut., uterus; Vg., vaginal plate; yl.P., anal plates. The larval bud, lying 

 across the intestine, is shown in b, and its position in the larva in c. The 

 results of transplantations of fragments of the bud are summarised in d, 

 which shows the overlapping fields from which the various organs are 

 formed (shading corresponding to those of Figure a). (After Hadorn and 



Gloor 1946.) 



argues, on the basis of aberrant types of development found in certain 

 mutant stocks, that the essential features of the imaginal buds are deter- 

 mined by influences from the mesoderm which migrates into the buds 

 during the third instar. Thus the determination of the buds which occurs 

 in the embryo can only be of a preliminary and tentative kind. 



Even during the period of pupation, some degree of regulation is 

 possible to the various imaginal buds. Waddington (1953) and Pantelouris 

 and Waddington (1955) found that if one of the mesothoracic buds is 



