398 



The changes, then, which the respiratory system under- 

 goes during metamorphosis — a re-development of the longi- 

 tudinal trunks, the formation of a new spiracle, development 

 of new tracheoles from tracheolohlasts, the production of the 

 air sacs from purely embryonic cells, and, finally, the dis- 

 appearance of ancestral stigmata^ — are identical with the 

 changes, which have been going on during early larval life 

 (and probably during embryonic life, if these were known), 

 or which would have gone on had the whole of the develop- 

 ment from egg to adult taken place within the egg membrane. 

 The significance of this will be discussed in the second part 

 of this paper. 



The destruction of the epithelium of the main tracheal 

 vessels by leucocytes has been described by Perez (1910) in 

 Calliphcyra ; but, so- far as I am aware, the general disintegra- 

 tion and total renovation of the branching vessels have never 

 been observed. 



The conclusions of Breed (1903) and of Anglas (1904) 

 that tracheoles are not formed as direct outgrowths from the 

 main trunks appears to be quite erroneous, and the criticism 

 of Poyarkofif, that Anglas was really dealing with myoblasts, 

 seems to me entirely justified, since these cells in Nasonia 

 "frequently show a remarkable resemblance to small nucleated 

 tracheoles. 



THE MUSCULAR SYSTEM. 



The history of the muscular system during post-embryonic 

 life will best be considered under the following headings : — 

 (a) The anatomy of the larval muscular system; (b) the 

 structure of the larval muscles and their post-embryonic 

 development; (c) disintegration of the larval muscles; (d) 

 regeneration of the muscular system. The last section will 

 be considered under various headings, viz.: (1) Tlie longi- 

 tudinal abdominal muscles; (2) the vertical abdominal 

 muscles; (3) the pharyngeal dilators; (4) the muscles of the 

 mouth appendages; (5) the muscles of the legs; (6) the ovi- 

 positor muscles; (7) the great thoracic muscles (muscles of 

 flight); (8) the intestinal muscles; (9) the muscle insertions. 

 An examination of all these different muscles, moreover, will 

 enable a comparison to be made between them. 



The Anatomy of the Larval Muscular System. 

 Although the individual muscle fibres of the larva 

 undergo a considerable amount of differentiation during larval 

 life, yet the general anatomy of the muscular system does 

 not alter. I shall describe it here as it can be observed in 

 living larvae in the first instar, before they have become too 

 gorged with food to be sufficiently transparent for observation. 



