6t R. J. TILLYARD. 



71 



which the capillaries arise. Only in the capillaries themselves 

 is there no pigmentation. The capillaries also differ from the 

 larger tracheae in lacking the spiral thread of the endotrachea, 

 which is quite conspicuously visible in sections of the larger 

 trachea*. The nuclei of the ectotrachea closely resemble those 

 of the hypodermis, and their structure is practically the same A 

 transverse section through one of the main tracheae of Calopteryx 

 is shown in Text-fig. 9, while a comparison of the ectotrachea* 

 with the hypodermis in Argiolestes can be made by referring to 

 Plate vi., tig. 44. 



Text-tig. 10. 

 Capillary loops of tracheal system at extreme tip of s^ill {)i Avxtroaririon 

 cyane (8elys); ( x 370). Drawn from the freshly cut-off" <fill. 



Each trachea lies in a narrow portion of the hajmoccele, closed 

 off, usually, by the alveolar meshwork, sometimes in part by the 

 internal laminfy or the hypodermis. This narrow channel is not 

 easily discovered in most sections, but when it encloses some 

 blood-plasma, as it sometimes does, it can then be clearly deter- 

 mined, as in Text-fig.9. 



