116 
Psyche 
Third Instar 
[December 
Head width, .68 mm. Killed early in period of cell division 
and growth preceding fourth instar. The old endoeuticula 
is partly resorbed and the new integument is partly secreted. 
The apposition of nerve and trachea is the same as that of 
the preceding instar. Costa communicates anteriorly and 
posteriorly with the hsemocoele and does not contain a tra- 
chea. Subcosta appears for the first time in the life history 
of Pteronarcys proteus during the period of hypodermal cell 
division in the last phase of the third stadium. Subcosta is 
open at the anterior end and opens posteriorly into costa 
at a point near to where the latter empties posteriorly. 
In the right forewing 48^ posterior to the entry of the 
trachea onto the wing epithelium, one observes the opening 
of subcosta, and 30p. posterior to that opening is the point 
of entry of the trachea into the lacuna. The trachea is there- 
fore associated with the wing epithelium for 78p. without 
having created an intercellular space, much less a lacuna. 
Once within the subcosta, the trachea travels for 48p. and 
moves from the dorsal to the ventral epithelium. The tra- 
chea ends outside of the lacuna 6^ before subcosta ends. 
With minor variations the behavior of the trachea in each 
of the three subcostas is the same. A small cross vein has 
already developed 60p. anterior to the distal end of subcosta. 
Because the entry of the trachea into subcosta is so far 
removed from the anterior opening of the lacuna, subcosta 
could not possibly have been induced by the mechanical bor- 
ing in of the trachea. Subcosta is not centered with respect 
to the trachea once it does enter. The lacuna does not taper, 
whereas the trachea tapers to nothing. Evidently the trachea 
does not induce the lacuna. 
Head width, .79 mm. Killed late in period of cell division 
and growth prior to the moult to the fourth instar. Exami- 
nation of the integument showed the old integument to be 
almost completely resorbed and the integument of the fourth 
instar in great part to be laid down. 
The structure of the wing in this specimen differs from 
the early growth phase third instar. At the anterior margin 
of the wing a large trachea becomes applied to the dorsal 
wing epithelium. 24[x posterior to the point of application 
a lacuna appears but is not associated with the trachea. The 
