44 THE LIFE-STORY OF INSECTS [CH. 



life. Among the flies of the bluebottle group (Mus- 

 cidae) the brain (fig. Hi?) is situated, as in Chiro- 

 nomus, in the thoracic region of the legless maggot, 

 which is the larva of an insect of this family, and 

 the imaginal discs for eyes and feelers (fig. 11 e,f) 

 lie just in front of it. Here, the imaginal buds of 

 the legs (fig. 11- -1, 2, 3) and wings (fig. 11 W,w) are 

 deeply inpushed, retaining their connection with the 

 skin only by means of a thread of cells. As the larva 

 is legless and headless its outer form is not affected 

 by the discs and it is not surprising to learn that they 

 appear early. It has indeed been suggested that the 

 pharyngeal region of the larva, in connection with 

 which the imaginal head-discs are developed, should be 

 regarded, though it lies in the thorax, as an inpushed 

 anterior section of the larval head. In any case this 

 region is pushed out during the formation of the 

 pupa within the final larval cuticle, so that the 

 imaginal head with its contained brain, its compound 

 eyes, and its complex feelers, takes its rightful place 

 at the front end of the insect. 



The mention of the brain suggests a few brief 

 remarks on the changes in the internal organs during 

 insect transformation. There are no imaginal discs 

 for the nervous system ; the brain, nerve-cords and 

 ganglia of the butterfly or bluebottle are the direct 

 outcome of those of the caterpillar or maggot. More 

 than seventy years ago, Newport (1839) traced the 



