io8 The Fly of Chironomus 



a circumstance which tells in favour of Leydig's sup- 

 position that they are primarily respiratory organs — • 

 a supposition which is far from general acceptance at 

 present. We can give no account of the function of these 

 organs in Chironomus. 



The Malpighian tubules persist unchanged throughout 

 the metamorj^hosis, being, we may suppose, still required 

 for the elimination of the abundant waste material 

 formed by the destruction of various larval tissues. 

 Heart. We liave seen (p. 71) that in the larva the contractile 



and valvular heart is restricted to the hinder part of the 

 body. As the tracheal system attains a fuller develop- 

 ment, the part of the dorsal vessel in front of the original 



heart becomes chambered. New 

 inlets and valves apj^ear, and 

 the muscular tissues become 

 ^/sT'y-^ "^^^^W ii^ore complex. In the late 

 ^1^^\%Z]/ larva, pupa, and fly, the dorsal 



X.,.^.'^-^'' vessel is chambered throughout 



the abdomen. In the pupa and 



Fig. 78 — Transverse section <>t' ^ 



rectal papilla of fly (from larva), fly the tllOracic pOrtioil of the 

 X 300. '^ 5 . 



dorsal vessel exhibits a feature 

 which we have not found in early larvae, viz. a numerous 

 series of what we take to be ganglia, placed alternately 

 on the right and left sides in the neighbourhood of the 

 head. These were also found in the larva of Corethra by 

 Dogiel (1877). 

 Tracheal The two paii's of tlioracic spiracles of most insects 



system. 



are now believed to belong to the meso- and meta- 

 thorax. This has been proved for several Coleoptera ' and 

 Hymenoptera (A^Dis, Hylotoma), Hemij^tera (Coccidae), 

 and Thysanura (Lepisma). We believe that no clear case 

 of a prothoracic spiracle has been recorded in any winged 



' See Heider on Hydroj)hi]u-^, Wheeler on Doryplioia, Graber on Melo- 

 lontlia and Lina. 



