THE BIOLOGY OF THE CHRYSOPIDAE 325 
THE ADULT 
Expansion of the wings and darkening of the veins 
The imago generally walks abovt excitedly for a few seconds, going 
a short distance and then coming to a stop with the end of the abdomen 
downward. This position facilitates the spreading of the wings. If 
the supporting surface be turned upside down repeatedly, the imago will 
just as often assume its first position. The wings expand presumably 
by blood pressure, the expansion beginning at the base and extending 
outward. The tips are the last to expand, usually requiring a half 
hour before being fully expanded. 
The veins and veinlets of the wings are wholly green at first, but 
certain ones soon begin to darken, first at the basal part of the wings and 
lastly at the outer parts. The adults of Chrysopa oculata exhibit a 
variation in this respect, from entirely green to fairly dark. A series 
may readily be arranged, including perhaps twenty individuals, with a 
gradual succession of changes in the extent of pigmentation of the veins. 
C. nigricormis also shows considerable variation. The first veins to 
darken are the gradate series, between the branches of the radius. The 
costal veinlets and the ends of the branches darken next. The base of 
M;..4 (the divisory veinlet) has not been observed to be a true index to 
the degree of darkening of the wing. 
Voidance of larval excrement 
The black mass of larval excrement which was seen near the end of 
the abdomen of the pupa, and which, in the newly emerged adult, can be 
readily located, still must be voided. The voidance appears to require 
considerable effort, and is accomplished from five to fifteen minutes after 
the wings are expanded. — 
Tracheation 
Pupal tracheation 
The camera-lucida drawings of the pupal tracheation (Plate LX XVIII) 
show clearly its essential points. The costal trachea appears as a very 
short and rather indistinct trachea at the usual place. It has been over- 
looked by other workers, but in the course of these studies it has been 
seen repeatedly in Chrysopa oculata and C. nigricornis. The branch 
M, is so close to Rk; that it appears to be a part of the latter. Tillyard 
(1916-17) has so interpreted it in C. signata, but in both C. oculata and 
C. mgricorms it is clearly a medial branch. A similar condition exists 
in the cubital region. The outer branch of the cubitus appears super- 
