570 The Structure of the Trachee. of Insects. [June, 
3. Wall of Trachee—This discovery leads to wider results. 
The pseudotrachee so closely resemble the salivary duct and the 
proper trachez that all these structures have been frequently 
confounded together. The pseudotracheze being surface-produc- 
tions are open externally by a longitudinal slit. The salivary 
duct and proper trachez, being internal structures, do not admit 
of a lateral fissure, but they are ingrowths from the surface, and 
are morphologically of the same nature as the pseudotrachee. 
Hence we may expect them to be produced on the same princi- 
ple. If the pseudotrachezee are demonstrated to be thickened 
crenulations of the external cuticle, we are led to ask whether the 
spirals of the proper trachez and of the salivary duct are not 
crenulated thickenings of the intima. 
The fragment of a trachea of a centipede (Fig. 2) bears out 
this interpretation. Above A is a rent with a small fragment of 
the membrane supporting 
relics of spirals, which are 
probably phere ól 
losing themselves below. 
This is very unlike what 
would appear if the sp 
_Fic. 2.—Part of trachea (centipede) with were independent stric- 
sa * tures, Whenever the 
n is artificial, as the 
re what is comms" 
é remaining '™ 
separates from the membrane the separatio 
membrane is easily rent. We never find he | 
in plants, the spiral unrolling with the membran 
: o be continua” 
tact. In fact, membrane and spiral here appear r ie in to 
tions of each other, the membrane thickening and tu of 
ws 
form a fold, somewhat after the pattern of the bello ; 
accordeon. Minot’s observations about 
away, several together, and about their tape 
and gradually disappearing, find their exp 
ring down to apr 
on in this. * 
pattern of b 
pendent threads, and is identical with the ws 
which we 
the “ catch-drain ” of the pseudotrachee, 
to be crenulations. elves af 
A result of this éxplanation is, that the spiral i gea cours 
fine tubules, externally opening by a fissure along 
the spirals often CON 5 
