846 THE AMERICAN NATURA... 
ere 
germanica! remains the only considerable atte 
making of the wing in an insect with incomplete : 
In this chapter we give the results of some studi 
have endeavored to follow the phylogenetic or. | 
development. 
It is not necessary to trace in this place the steps 
the present state of knowledge of wing development kv 
82.— Wings of nymphs: A, of a stone fly 
from nymphs one third grown ; et C and F from 
nymphs that were three fifths grow 
reached ; for this has. 
well done by several wrt. 
Among the more complet 
of these summaries are those - 
of Gonin? and of Pratt.® 
Neither does it seem 
desirable to enter into a 
detailed discussion of con- 
troverted points, our object 
being merely to state what 
is definitely known on this 
subject, and to add the re- 
sults of some of our own 
investigations. 
It is well known that the 
wings of insects arise as 
sac-like folds of the body 
wall of the second and third 
thoracic segments. These 
folds first appear at the 
point where the suture be- 
tween the tergum and the 
pleurum later develops. In 
most insects with incom- 
plete metamorphosis they 
are so directly continuous with the tergum and become so solidly 
chitinized with it that they have generally been interpreted as 
outgrowths from its caudo-lateral margin (Fig. 82, A, B). 
1 Rehberg, A. Jahrd. d. k. Gymn. zu Marienwerder, 1886. 
2 Bull. de la Soc. Vaud. des Sci. Nat., vol. xxi, pp. 90-98. 
8 Psyche, vol. viii (1897), pp. 15-30. 
