568 The Structure of the Trachee of Insects. [June, 
vascular system in spiders, showed that in both groups the circu- 
lation is essentially lacunar. 
Recent investigation has established the doctrine that the trach- 
ez and also the trachea-like salivary ducts are chitinous products 
of ingrowing processes of the epidermis. Bütschli deems them 
segmental paired invaginations of the epidermis, while Weismann 
finds that the tracheal wall is an intima secreted by ingrowing 
rows of cells, just as the chitinous cuticle is secreted by epider- 
mal cells? These discoveries are of fundamental importance, and 
must underlie the true theory of the nature of tracheal struc- 
tures. 
The views of some other investigators seem to me not so well 
established. Meyer, for example, finding that the intima (the 
name here used to designate the chitinous wall of the trachea) 
arises as a homogeneous membrane, holds that it subsequently 
splits so as to give off a spiral thread, and that the larger trunks 
have a double membrane external to the spiral.” Carl Chun sup- 
poses that the spiral thread is a true chitine layer, and not merely 
a thickening product of the intima, and superadds a splitting of 
the intima into a double membranet C. S. Minot represents the 
spiral filaments as solid threads imbedded in the substance of 
the chitinous intima, and adds some good observations = ee 
spiral threads (sometimes two to five or six together) ending = 
a few turns round the trachea, “ the single threads perma g 
abruptly but by tapering down to a point and so disapprai 
None of these observers seem to see, much less to grapple w 
the difficulty of conceiving how the spiral filament or me 
else can be formed external (morphologically) to the wig? 
secretion of the epidermis, or how such chitinous outgro 
split after they are once formed. oboscis ol 2 
2. Pseudotrachee of Muscide.—In examining the pr a 
1 Blanchard in Ann. d. Sci. Nat., Ser. 3, Vol. 1X (1848), and An 
Nat. Hist., Ser, 1, Vol. xx. Joly in Ann. d. Sct. Nat., Set 3+ Vol. yo Nate : 
Agassiz in Proc. Amer. Ass. Adv. Sci., 1850. Claparède in Ann, ¢. 
5, Vol. 11 (1864). 
3 Zeit. f. Wiss. Zool, XUI, XIV, XVI (1863-186 
‘ 
xx (187% 
Bütschli). l 
6, Weismann) , 
3 Zeit. f. Wiss. Zool., 1 (1848). pachten, T PIS 
t Inaugural dissert., “ U. d. Bau u. der Rectaldrüsen b. d. : 
1876. Recherchë = 
5U. S. Entomol. Comm. on Locusts, Report 11, p- 192 (1880), Ba is 
tolog'ques sur les trachées del Hydrophilus piceus, in Archiv. 4€ 
