OF THE TRACHEA IN INSECTS. 33 



Interganglionic Commissures. (PI. I. figs. 2 & 7.) 



It might have been expected that the tracheae on these organs would have resembled 

 those on the ganglia, and at any rate that tracheae would either have been present or 

 absent in all insects. Both suppositions, however, would have been wrong. The tubules 

 in the ganglia are usually straight, while those on the commissures are generally waved, 

 besides difi'ering in other respects. Again, in Fentatoma and all the Lepidopterous larvae 

 which I have examined, the commissures are very richly supplied ; in Bombus, the Diptera, 

 and some Coleoptera, they are less numerous ; while in some Coleoptera, the Orthoptera, 

 Lepidoptera, and Neuroptera, the tracheae are either rare or altogether absent. This 

 at least holds good as far as my observations go ; but the statement wiU no doubt be 

 modified by further investigations. 



Between two of the thoracic ganglia in the larva of Acheta I found one of the com- 

 missures pretty well supplied "svith trachea?, while the other was quite free from them. 

 Indeed generally throughout insects the tracheae on the tAvo nervous columns are not 

 arranged in exactly the same manner. 



In Scarabceus, Necrophorus vespillo, and N. humator, the tracheae on the commissures 

 and on many nerves were in tufts resembling those of the ganglion, except that they 

 are altogether smaller, that the tubules branch oftener, and that they are more waved. 



In Cerambyx moschcdus also the commissures were well supplied with tracheae. In Sy- 

 drophilus piceus the tracheae were like those of Necrophorus, but in some cases I observed 

 branchlets which did not form tufts. The tubules were numerous and very delicate indeed. 

 In Musca and EristaUs the tracheae were in tufts, very much like those on the gangKa, 

 but with straighter tubules. The nerves, however, were almost entirely free from tracheae. 

 In Tipula the tracheae were numerous. In the larva of Lucanns the commissures were 

 well supplied, but in Carabus, the larva of Lampjyris, and in Forjicula, both they and the 

 nerves were almost entirely free from tracheae. Tn Acheta, Locitsta, and Gryllus also, the 

 abdominal commissures had only here and there a single trachea, which seemed as it Avere 

 to have strayed out of a neighbouring ganglion. In these cases I have not examined a 

 suflRcient number of specimens to prove that these single tracheae are inconstant, but I 

 have little doubt that this is the case. The thoracic commissures of Acheta, and also of 

 its larva, were provided with decidedly more numerous tracheae, which are a little waved 

 and give out single branchlets which again divide once or tAvice. 



In Noctua the tracheae are like those of Acheta, but rather more numerous, tAVO or 

 three generally running nearly to the middle of the commissure. They are seldom, if 

 ever, branched, and are almost straight. On those of CampcBa margaritaria, jPieris napl, 

 Sipparchia janira, Callimorpha jacobmoi, and Tterophorus, I found no tracheae. On the 

 contrary, in the larvae of Euplexia lucipara and Oonepteryx rhamni they Avere Avell sup- 

 plied ; and in the larvse of Lasiocampa rubi and Mamestra they were very numerous both 

 on the commissures and nerves. On the commissures of Bombus nmscorum they are nu- 

 merous, waved, and generally in tufts consisting of a feAv branched tubules, sometimes 

 even of only two. On those of Athalia spinartim, Tenthredo, Ichneumon (probably) ex- 

 tensorius, and another small black species, I found none. On those of Ophion there 



VOL. XXIII. F 



