THE RESPIRATORY ORGANS. 



4. THE RESPIRATORY ORGANS. 



The trachese of the larva consist of two main longitudinal 

 trunks (Fig. lo), which give off numerous lateral branches. 

 These divide and subdivide, and their terminal divisions form 

 a dense network of exceedingly fine tubes, tracheal capillaries, 

 in the peritoneal investment of the various internal organs. 



KiG. II. — Details of the tracheal system of the adult larva. I, a stction through the 

 posterior spiracle, :J-iiu:h objective ; 2, a section through one of the stigmatic 

 slits ( -[V oil immersion) ; 3, section through the .interior spiracle ( .V oil immer- 

 sion) ; 4, a portion of a tracheal trunk, ^ ol>jective ; 5, tracheal terminations^, 

 peritraciieal cells (peritoneal coat) ; tr, trachea ; v, vestibule ; s, slits ; h, nuclei 

 of peritracheal cells ; e, mesoblast cells ; pr, fibres of the vestibule^,?-, grating 

 of the slits ; ul, imaginal disc of the anterior spiracle (upper prothoracic disc). 



Leydig* correctly maintained that these capillaries are de- 

 veloped in the interior of the cells of the connective tissue, but 

 Wistinghausenf has quite recently described them as between 



* Leydig, Fr., ' Zum Feineren Baudes Arthropoden.' Miiller's Archiv., 1855. 

 t Wistinghausen, ' Ober Tracheenendigungen in den Sericterien der 

 Raupen.' Zeitsch. f. \v. Zool., Bd. 49, p. 565. 



