48 
MR. LUBBOCK ON THE DISTRIBUTION 
on the other hand, a side branchlet forms a separate system at right angles, or nearly so, 
to the first. 
On the thoracic mnscles of Chrysopa the branches end in small fan-like tnfts of tubules. 
In the larva of Lasiocampa rubi the tracheae are numerous, simply branched, and much 
waved. In the larva of Mamestra brassica? they are very similar, but straighter. 
In jffipparchia Janira, Pieris brassicte, and Amphimalla solstitialis, 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 
Musca the tracheae were very similar. In Tipula the tubules were longer than in Musca 
or Eristalis. In Necrophorus the saccular tracheae resemble those of Eristalis ; but the 
tubules are longer. 
In the Cricket they resemble those of Panorpa (PI. IV. fig. 18). Some parts more 
resemble PI. IV. fig. 12. Locusta and Gryllus did not apparently differ from Acheta. 
In the larva of 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 tujmles also which arise from them are long and only 
branched here and there. 
Aphrophora has tracheae of the usual type. In Pentatoma the parallel saccular trachea 
are narrower than in Eristalis, being only about T^ooth of an inch 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 laws 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. 
First, 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 different 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 Pentatoma, 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 (PL I. fig. 16) which end the branchlets, are very different in size in the 
different parts. A smaU 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. 
Fifthly, while in the larva of Orthoptera the tracheae very closely resemble those of the 
