PLATE XX 



Figure 1. The respiratory system of Culex. c.tr., cervical 

 trachea, a.s., anterior spiracle, with its large trachea, 

 p.s., posterior spiracle. d.a., dorsal arch, running 

 below the heart, l.tr., lateral trachea, a.tr., trachea 

 anastamosing with one from the next spiracle : simi- 

 larly in the other segments. The abdominal spiracles 

 are numbered in order. 



Figure 2. A section through the thorax of Haeinatopota, to 

 show the muscles, l.m., the longitudinal muscles, 

 v.m., the vertical muscles, tr., trachea, d.c., the 

 duct of the crop, sl.g., the salivary glands, pv., 

 proventriculus. n., nerve cord. Note the membra- 

 neous area in the lateral wall, x 45 about. 



Figure 3. Respiratory system of Tabaints. br., brain, a.s., air 

 sacs, ab.s., first abdominal air sac. ab.s'., second 

 abdominal air sac. Other letters as in Figure 1. 



Figure 4. A trachea, highly magnified, to show the spiral thread, 

 and the nuclei of the hypodermal cells which lie on 

 the visceral surface. 



Figure 5. The anterior thoracic spiracle of Miisca, to show the 

 fine arborescent filaments of chitin which guard the 

 entrance to the trachea. X 440. 



Figure 6. The tracheal sacs supplied by the anterior thoracic spir- 

 acle (a. th.). In this figure the tracheal sacs supplied 

 by the posterior thoracic spiracle and the sterno-dor- 

 sales muscles of the left side have been removed. 

 n'M^-tu ^ ne ^ rst abdominal segment has been removed to 

 show the large abdominal air sacs (ab. s.) and an 

 abdominal trachea which is supplied by the second 

 abdominal spiracle (a. sp.). After Gordon Hewitt. 

 A. c. s., anterior cephalic sac. a.v.s., anterior ventral 

 thoracic sac. c.tr., cervical tracheal duct. d.c., 

 dorsal cephalic sac. do., dorsales muscles. H., 

 haustellum. l.tr.s., longitudinal tracheal sac. p.c.s., 

 posterior cephalic tracheal sacs, p.v.s., posterior 

 ventral thoracic sac. p. op. periopticon. Ros., Ros- 

 trum, v.c.s., ventral cephalic sac. 



