32 MR. LUBBOCK ON THE DISTRIBUTION 



inferred ttiat tlieir ultimate structure also varies less than that of other parts. The 

 ganglia are always well and often very richly supplied with tracheae, differing in this 

 respect from the commissures and nerves, which in many insects (as mentioned helow) 

 are entirely free from them. The tuhules, excepting sometimes those which are distributed 

 to the surface, are straight or gently curved, but not waved. They generally rise singly 

 from the branch] ets, as in PL I. fig. 1 ; but sometimes, even in the same insect, we find 

 tufts, as in PI. I. fig. 3. 



The abdominal ganglia in Bombus terrestris and JB. lapidarius, are covered over with 

 a network of tracheae. The meshes vary much in size, from -g-^ inch in length and 7^ 

 inch in breadth to less than -^oih. of that size. The tracheae forming the network are 

 of considerable breadth, averaging perhaps -awo i^ich. The short commissure between 

 the posterior and penultimate ganglia has as rich a network of air-vessels as the ganglia 

 themselves. 



These latter are penetrated by niimerous branches which end in tufts (PI. I. fig. 3) 

 of from five, or even sis, down to two or three. The tubules branch two or three times, 

 and resemble a fishing-rod in their general proportions and curvature, running in a gentle 

 sweep often for j^o inch, with a thickness at the base of only tto 00 inch. 



The ganglionic tracheae of Fanorpa, lAbellula, Carabus, and AphrojjJwra are like those 

 oi Bombus; and so are the tracheal tubules of Vespa, Tenthredo, Athalia spincmmi. 

 Ichneumon (probably) extensor'ms, Ophion, Clirysopa, Tipula, Campcea margaritaria, 

 Callimorpha Jacobs (B, Pterophorus, and the larva of. Euplexia lucipara; but I am not 

 sure whether the branches end in tufts. In none of them is there a network enclosing 

 the ganglia, as in Bombus. 



In the larva of Lampyris, AmpjMmalla, Aclieta (both larva and imago), Lociista, and 

 Gryllus, the tubules are larger and longer, but otherwise very similar. The branches, 

 however, do not end in tufts. 



In Forficula the tracheae resemble those of Acheta, but are smaller. 

 In NecropJiorus Jmmator, N. vespillo, Scarabceus, and Musca, in Sip)parcliia Janira, 

 Pieris ncqn, Noctua gamma, the larva of Basiocampa i^iibi, of Mamestra brassiccB, of 

 Oonepiteryx rJiamni ; the tracheae sometimes end like the preceding, and sometimes in 

 tufts, a large branchlet ceasing suddenly and giving off from four to seven or more tubules. 

 These latter divide and re-divide again, sometimes breaking into little secondary tufts. 



In the larva of Musca the mode of branching is quite unlike that of the imago, being 

 simple and not in tufts. 



In Sydrous pncetis the tracheae are in tafts ; but the tubules rising from them are 

 nearly of uniform size, so that there are no secondary tufts. 



In Eristalis the tracheae of the ganglia break into tufts like those prevalent throughout 

 the body. Upon the surface they are waved and resemble those of the commissures ; but 

 in the interior of the ganglion they seem to be straighter. 



In Pentatoma large wide tracheae go to the ganglia, and give off short thick branches. 

 These again give off still shorter branchlets, which end in tufts consisting each of a few 

 straight tubules (PL I. fig. 5). 



