194 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
the walls are contracted. This shows, as I also know from direct obser- 
vation, that the trachea?, though capable of great elongation, are more 
easily bent than compressed, so as to diminish their length. Around 
the organs of more elongated form the branches of the tracheae run 
more longitudinally, as is shown by the air tubes of the muscles, which 
also present some peculiarities worthy of especial notice. A short thick 
trunk (see Fig. 12) arrives at the muscular bundle, and, dividing very 
rapidly, breaks up into a large number of delicate tubes, which pene- 
trate between the muscular fibers, there terminating in tubes of exceed- 
ing fineness, which, at first sight, seem to form a network that might 
well be called a rete mirabilc. A closer examination, however, reveals 
that it is not a real network, but rather an interlacing, confusing to"the 
eye. The longitudinal direction of the trachea} of the muscles presents 
a striking contrast to the system of divarication, represented in Figs. 13 
and 14. The course of the trachea? of the Malpighian tubes is also very 
curious. It is represented in Fig. 10. There is one large trachea which 
winds around the tube in a long spiral, giving off numerous small 
branches, which run to the surface of the tube, upon which they form 
delicate ramifications. Each tube has but a single main trachea, and I 
think the trachea continues the whole length of the tube, but of this last 
point I am not quite sure. 
Many organs, as for instance the testis of Anabrus (Fig. in the text), 
are supplied by a few large tracheal trunks, which give off many small 
branches, the ramifications of which penetrate the organ in question. 
The fine terminations of the trachea? have been investigated, as far 
as I am aware, only by Max Schultze, 249 Weismann, 250 and LL Meyer. 251 
They all agree in stating that they end blindly in stellate and branch- 
ing cells. Max Schultze discovered that these terminal cells are dyed 
black by per-osmic acid, so that they are then very sharply marked off 
from all the surrounding tissues. The trachea? extend into the interior 
of these terminal cells. Graber 252 gives a singular account of the termi- 
nation of the trachea? in Phthirius Uujuinalis. I cannot but think that 
his description is based upon a false interpretation of his observations. 
The development of the trachea? has been studied by Weismann and 
Meyer in the papers just cited, and also by Semper, 253 in an admirable 
paper on the development of the wings in Lepidoptera. 
Dr. Williams, in his article published in the Annals and Magazine of 
Natural History for 1854, vol. xiii, maintained that the finer branches 
anastomosed, resembling in that respect the capillaries of vertebrates. 
Lubbock has already pointed out that the tracheal anastomoses are con- 
2,3 Max Sch ultze : Zur Kenntniss der Leuchtorgano von Lamp yris splendidula. Arch. f. mikros. Anat 
1, p. 124 j Trachcen, p. 130, £f. ; figs. 4, 5, 8, and 9. 
"° Weismann : Die Entwickelung der Dipteren im Ei. Zeitschrift fur Wiss. Zool. Bd. XTTT (1863), p. 193. 
251 H. Meyer : Ueber die Entwickelung des Fettkorpers, der Tracheen und der keimbereitenden Gesch- 
lechtstheile bei den Lepidopteren. Zeitsch. f. wiss. Zool. Bd. I, p. 174. 
K'Oraber: Zeit. f. Wiss. Zool. XXII, 147 (1872). 
^Zeit. Wiss. Zool. VIII, p. 328. 
