88 THE LARVA OF THE BLOW-FLY. 



Viallanes [27, p. 66] describes the dorsal vessel of a young 

 dipterous larva, which he refers to the genus Ctenophora, in 

 which he observed tufts of fine tracheas in the pericardium, and 

 the connection of the dorsal vessel with the transverse anasto- 

 motic tracheal trunk. He adds : 



Fig. i8. — The dorsal vessel : /, a semi-diagrammatic representation of the two 

 posterior sections, showing the large cells of the pericardial septum, the alse 

 rnuscularcs and the cell fringes ; 2, the anterior eNtremity of the aorta and the 

 ""g ; 3^ ^ transverse section of the intermediary portion ; 4, a longitudinal sec- 

 tion of the same, with a pair of valves, seen from aljovc, sliowing the internal 

 cells, cell fringes and aLx musculares ; 5, a lateral view of a valve pouch — [V o" 

 immersion lens. 



' It appears, therefore, that in this larva the dorsal vessel is 

 an arterial heart, since the blood which enters it has passed 



