THE ANATOMY OF THE PUPA 71 



described by Major Ross, I.M.S., by an observer not per- 

 sonally conversant with the appearances of the two struc- 

 tures ; and I shall not be at all surprised to find descriptions 

 of these bodies appearing in the form of notices of the 

 occurrence of the parasites in the pupal stage. The possi- 

 bility of the communication of the disease among Mosquitoes 

 through infected ova has already been mooted, and investi- 

 gators working upon this line should be on guard against 

 this fallacy. 



The so-called aorta runs from the anterior end of the 

 dorsal vessel forwards, above the stomach and oesophagus 

 to the head, where it terminates in an open end. In trans- 

 verse sections of the thorax the aorta appears as a laterally 

 compressed tube, and does not appear to give off any 

 branches. 



The respiratory system, during pupal life, undergoes the 

 changes which prepare the rudimentary stigmatic trunks of 

 the thorax and abdomen to take on functional characters in 

 the adult. With the exception of the first abdominal pair, 

 however, none of the stigmata are open except the pro- 

 thoracic openings which form the respiratory syphons. 

 These first abdominal stigmata open into the air space 

 which exists under the pupal skin beneath the thorax, and 

 in which the legs are undergoing development. This cavity 

 must exercise a hydrostatic function, and the patency of 

 these stigmata must be in this case necessary for the con- 

 veyance of air to the cavity. From the base of each syphon 

 tracheae run to various parts of the body and head. Among 

 these may be mentioned specially one transverse trunk 

 running across the thorax between the alimentary canal and 

 the nerve chain, which puts the two syphons in direct com- 

 munication with each other ; and a pair of longitudinal 

 trunks ranning back to the hinder end of the body, and 

 giving off branches to the various organs, and also a branch 

 to each of the future stigmata. 



The cuticular lining or intima of the chief trunks and 

 their branches is well developed even at the beginning of 

 pupal life, and has the usual spiral thickening. The trunks 

 connecting the stigmata with the main trunks are the only 



