118 
Psyche 
[December 
membranes to form a middle membrane. Prothoracic lacu- 
nae therefore differ histologically from vein lacunae in having 
a diameter from 2^ to 4 times as great, and are not middle 
membrane structures. 
From a study of the early instars of Pteronarcys proteus 
one concludes that: (1) the sole histological distinction of 
vein lacunae is their middle membrane structure. One can- 
not say that vein lacunae are also distinguished by tracheae 
because costa rarely contains one, and costa in the early in- 
stars does not differ from subcosta or radius. (Costa, al- 
ways an ambient structure, did contain a trachea in one of 
about 60 examined specimens of all ages. The other longi- 
tudinal lacunae of older instars invariably contain both tra- 
cheae and nerves. Costa never contains a nerve.) 
(2) Lacunae are not induced by tracheae. 
The writer is particularly grateful to Dr. Albert Miller of 
the University of Arkansas who supplied specimens of the 
first and second instars, and to Dr. F. M. Carpenter and Dr. 
A. B. Dawson who read and criticized this paper. 
Bibliography 
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(Blatta) Germanica. Zool. Jahrb. Anat., 41 377-410. 
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gange. Zeit, Morph. Oekol. d. Tiere, 30 pp. 506-543. 
Kuntze, H. 1935. Die Fliigelentwicklung bei Philosamia cynthia 
Drury, mit besonderer Beriicksichtigung des Geaders, der Lakunen imd 
der Tracheensystem. Zeit. Morph. Oekol. d. Tiere, 30 pp. 544-572. 
Marshall, W. S. 1913. The Development of the Wings of a Caddis- 
fly, Platyphylax designatus Walker. Zeit wiss. Zool. 105 pp. 574-597, 
3 pis. 
Sulc, K. 1911. TJeber Respiration, Tracheensystem, und Schaumpro- 
duction der Schaumcikaden Larven. (Aprophoringe-Homoptera) Zeit. 
wiss. Zool., 99 pp. 147-188. 
Tower, W. L. 1902. The Origin and Development of the Wings of 
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Description of Plate VI. 
Transverse Sections of Pteronarcys proteus Newport. 
I. Metathoracic flange, x294, first instar, right side. The site of 
the wing disc is marked by the transition of pavement epi- 
thelium to tall columnar cells. 
