44 
MR. LUBBOCK ON THE DISTRIBUTION 
In a smaller species of Musca, however, the tubules in each tuft were less numerous. In 
Dioctria Jlavipes the tracheee resembled those of Tipula and Tenthredo. In Fentatoma 
a single trachea runs up the terminal chamber of each ovary, and gives off branchlets 
from the side, as in PL III. fig. 11. The trachea ends simply. In Aphrophora spumaria 
(PL III. fig. 1) we meet with a type quite different from any of the preceding. Large 
tracheee proceed to the posterior end of the egg-tubes, where they rapidly break up 
into branches about 6 J th of an inch in diameter. These branches run all up the egg- 
tube, and half-way along the connecting filament, gradually diminishing in size till they 
can be seen no longer. They are nearly one-sixth of an inch in length, and do not give 
off a single branchlet. On one side of an ovary I counted sixty of these branches ; 
and there seemed to be as many on the other side. 
In Ranatra there are five egg- tubes. One single very large trachea, about Too^h of arL 
inch in diameter, passes to the upper end of the egg-tubes, where they reunite to form the 
common connecting filament, which was first described by Mliller. Here the trachea divides 
into about fifteen large trunks, each of which is about -gTmth of an inch in diameter. These 
trunks divide here and there dichotomously, and sometimes give off side branches ; but the 
distribution of air takes place principally by means of small lateral branchlets, which give 
off numerous long twisted tubes, and sometimes end finally in a small tuft. This con- 
tinues for about -njth of an inch, when all the trunks except six have exhausted them- 
selves, — each trunk ending in the same manner as one of the lateral branchlets ; but at 
these ends the tubules seem longer and more waved, and are not in tufts. 
The six trunks just mentioned pass along the egg-tubes for about yuth of an inch, with 
a diameter, excluding the so-called outer membrane, of a «& t hs of an inch, in which space 
they do not give off a single branchlet. Por about half of this distance the egg-tubes are 
supplied by the other trunks ; but for ^th of an inch after these have ceased, the egg- 
tubes are left free from tracheae. Por the last -g^-rd of an inch, the egg-tubes, and after 
that the oviduct and egg-canal, are supplied by the above-mentioned six trunks, and the 
mode of branching is the same as at the upper end of the egg- tubes. No tracheae are 
given to the generative organs from any other source. The tracheae on the oviduct are 
less numerous than those on the egg-tubes, and on the egg-canal they are fewer than on 
the oviduct. 
It is very seldom that we find a whole system of organs supplied, as in this case, ex- 
clusively by one great trunk ; and it is evident that here the air must pass to and fro in 
the same vessel. 
I was surprised to find six large trunks running along the five egg-tubes. The two 
ovaries agreed in this respect ; but I have not had an opportunity of examining other 
specimens, and therefore cannot say whether the number of these trunks varies or not. 
These six trunks run so far without a branch, and the branchlets arising from the 
other main trunks are so small in proportion, that the tracheae have much the same 
appearance at first sight as those of Aphrophora ; in that genus, however, the main trachea 
is at the posterior end, while in Ranatra it is at the anterior end, so that it is a case of 
analogy, and not of homology. 
At the end of October, when I examined this insect, there were no traces of egg-germs ; 
