E 
1884.] Thé Structure of the Trachee of Insects. 567 
by the glacial dam which I have supposed to have existed at Cin- 
cinnati. The facts had so impressed Mr. Squier that before know- 
ing of my discoveries he had come to the conclusion that there 
must have been some such barrier as I have supposed. (See 
Science, Sept. 28, 1883.) 
Strong as these confirmations are, it is important that the 
hypothesis of an ice dam should be verified by much wider ob- 
servations in the field. All along the Ohio river, and in all its 
tributaries above Cincinnati, there should be found numerous 
facts, explicable only by this theory ; while the absence of terraces 
ofa corresponding level upon the eastern side of the Alleghenies, 
to which Professor Lesley has called attention, excludes the 
hypothesis that these high terraces in the Upper Ohio are due to 
à general Champlain subsidence. 
Nor must the phenomena below Cincinnati be overlooked. 
During the summer of 1883, I continued my investigations into 
Southern Indiana to the Illinois line in Posey county. But I will 
hot here speak in detail of the results attained. The problem of 
determining the southern limit of the glaciated area of this region, 
ever, has been complicated by what I supposed to be the 7 
results of the Champlain subsidence, amounting to five hundred 
or more in the Mississippi valley. Here, for the first time in 
my western investigations, I have encountered: the loess overlap- 
Ping and intermingling with the terminal deposits of the glaciated 
area it a very interesting and puzzling manner. I hope during 
another Summer to get additional light upon the subject. Mean- 
while, I am anxious to obtain any information or instruction which 
the experience or wisdom of other investigators may be able to 
furnish me, 
203 
THE STRUCTURE oF THE TRACHEÆ OF INSECTS. 
BY PROFESSOR G. MACLOSKIE, D.SC., LL.D. 
ge *rical—Blanchard’s theory of two tracheal membranes 
2 i 
ties, vu was accepted by Louis Agassiz and some other authori- 
- Caride s Set aside as obsolete. It was well refuted by Joly; and 
nterposed spiral thread, and of peritracheal circulation, 
©, in refuting its author’s cognate theory of a complex 
