44 MR. LUBBOCK ON THE DISTRIBUTION 



In a smaller species of Ilusca, however, the tuhules in each tuft were less numerous. In 

 Dioctria JJampes the tracheae resemhled those of T'qmla and Tenthredo. In Fentatom.a 

 a single trachea runs up the terminal chamber of each ovary, and gives off branchlets 

 from the side, as in PI. III. fig. 11. The trachea ends simply. In Ai^lirophora spumaria 

 (PL III. fig. 1) we meet with a type quite different from any of the preceding. Large 

 tracheae proceed to the posterior end of the egg-tubes, where they rapidly break up 

 into branches about Troooth of an inch in diameter. These branches run all up the egg- 

 tube, and half-way along the connecting filament, gradually diminishing in size tUl 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 Banatra there are five egg-tubes. One single very large trachea, about xoo^h of an 

 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 -g^th 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 -^^i\). of an inch, when all the trunks except six have exhausted them- 

 selves, — each trunk ending in the same maimer 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 xoth of an inch, with 

 a diameter, excluding the so-called outer membrane, of i^jo o^lis of an inch, in which space 

 they do not give off a single branchlet. Eor about half of this distance the egg-tubes are 

 supplied by the other trunlcs ; but for i^otb of an inch after these have ceased, the egg- 

 tubes are left free from trachege. Por the last gVrd 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 trachete 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 trimks 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 trachese have much the same 

 appearance at first sight as those oi A2')hrophora ; in that genus, however, the main trachea 

 is at the posterior end, while in Banatra 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 ; 



