48 MR. LUBBOCK ON THE DISTRIBUTION 



on tlie other liancl, a side branclilet forms a separate system at riglit angles, or nearly so, 

 to the first. 



On the thoracic muscles of Chrysopa the branches end in small fan-like tufts of tubules. 



In the larva of Lasiocamim rubi the tracheae are niimerous, simply branched, and much 

 wared. In the larva of Mamestra brassicce they are very similar, but straighter. 



In Hij^parchia Janira, Pieris brassicce, and AinpMmalla solstltialis, the tracheae break 

 up into straight tubules, which diverge from one another. 



In Eristalis the thoracic muscles consist of broad ribbon-like tracheae, which lie parallel, 

 and near to one another, across the muscles. They end in finger-like prolongations, from 

 the end of each of which rises a small tuft of tubules, which are apparently very short. In 

 Musm the tracheae were very similar. In Tipula the tubixles were longer than in Miisca 

 or Eristalis. In Necrophorus the saccular tracheae resemble those of Eristalis ; but the 

 tubules are longer. 



In the Cricket they resemble those of Fanorpa (PI. IV. fig. 18). Some parts more 

 resemble PI. IV. fig. 12. Locusta and Gryllus did not apparently differ from Acheta. 



In the larva oi Acheta the tracheae in some parts resemble those of the imago. In parts 

 I found long ribbon-like tracheae, somewhat as in Eristalis ; only they are longer, nar- 

 rower, and further apart. The tubules also which arise from them are long and only 

 ln*anched hei'e and there. 



Apliropliora has tracheae of the usual type. In Pentatoma the parallel saccular tracheae 

 are narrower than in Eristalis, being only about -fooo^^ of ^"^ iiich in diameter. The 

 terminal tubules also seemed longer ; but I did not get a very good view of them. 



Conclusion. 



It would of course be rash to attempt to lay down general laAvs based on the examina- 

 tion of the few species which as yet I have been able to compare together ; but so far as 

 they go, my observations appear to point to the following conclusions. 



Eirst, that the same type of distribution regularly occurs in the homologous parts of 

 different specimens belonging to the same species. 



Secondly, that the same almost always holds good of homologous parts in different 

 species belonging to the same genus. 



Thirdly, that though the general type of distribution is the same in diflferent specimens 

 of the same species, yet the individual tracheae differ very much, — just, in fact, as we find 

 the general mode of branching is the same in different specimens of the Oak or Birch, 

 though in no two oaks or birches are the various branches and twigs exactly alike. 



Fourthly, that while in some insects, as for instance in Peutatoma, the tracheae in 

 many of the different organs have a different type of distribution, in others, as in 

 Eristalis, one type is found in most of the different organs. Even in this case, however, 

 the tufts (PI. I. fig. 16) which end the branchlets, are very different in size in the 

 different parts. A small organ has, as a general rule, more systems of tubules in a given 

 space than a large one ; but the relative proportions are, of course, not exact. Moreover, 

 even in this case, some organs (as, for instance, the muscles) are very unlike the remainder. 



Eifthly, while in the larva of Orthoptera the tracheae very closely resemble those of the 



