328 THE DEVELOPMENT OF THE NYMPH. 



Development of the Peripheral Nerves. Weismann held it as 

 probable that towards the end of the pupa stage, ' when the 

 differentiation of the limbs into skin, muscles and nerves 

 occurs, the newly-formed nerves come into relation with the 

 limbs through the medium of the nervous portion of the 

 imaginal pedicle.' 



Van Rees states that in every stage of the pupa which he 

 examined the nerves were demonstrable, extending from the 

 neuroblast to the tissue of the discs. This is my own view of 

 the subject, although in the early stages these so-called nerves 

 consist in the main of formative tissue, cells and fibres, but 

 contain no true nerve elements. It is very difficult to ascertain 

 in what manner the fibres are developed, but it appears pro- 

 bable that they first appear at the central end of these conduct- 

 ing cords, and grow towards the limbs, etc. ; but on this point 

 I am guided entirely by analogy, and have at present no abso- 

 lute evidence to offer. I hope, however, to have something 

 more to say on the subject when I describe the nervous system, 

 as I am at present engaged in some new researches on the 

 subject. As, however, it is one presenting extreme difficulties, 

 it is very probable that I may have to leave the development of 

 the peripheral nerves an unsolved problem. 



d. The Development of the Integument of the Abdomen. 



Ganin [34] was the first to recognise that the abdominal 

 integument of the imago is developed, like that of the head and 

 thorax, from imaginal discs. He says : ' Weismann quite 

 correctly states that the hypodermis of the eight abdominal 

 segments of the larva is not destroyed, but he was wrong in 

 supposing that the hypodermis of the larva is directly converted 

 by the division of its cells into that of the imago,' a change 

 which Weismann further states occurs at the end of the second 

 or beginning of the third day. Ganin, it is said, discovered 

 that the imaginal rudiments of the abdomen are already present 

 from the first days of larval life ; yet Viallanes says, ' According 

 to Ganin, the hypoderm of the larva becomes transformed into 



