70 West_, on the SJdn cast by an Ephemeron. 
settled and undergone its final ecdysis on the muslin curtain 
of one of the windows in the house in which I at present 
reside^ tidings were quickly brought to me^ and I succeeded 
in obtaining the specimen in beautifully perfect condition^ 
which forms the subject of the following notes. I regret 
much that the fly, which was also obtained in first-rate order, 
and which lived with me nearly twenty-four hours, was after- 
wards accidentally destroyed, so that I am unable to give the 
species. 
The entire cast measures eight lines in length, nearly five of 
which belong to the tails (PI. VI, fig. 8). The three divisions 
of the thorax are well indicated; the integument of the legs 
and of the antennae («, a, fig. 9) are very perfect ; the reticu- 
late corneal covering of both the sessile and the columnar 
pairs of compound eyes is left, the areolation being most dis- 
tinct on the latter. 
Behind the slit on back of the thorax through which the 
creature's body was extricated, is a mass composed of the 
pellicle from which the wings were withdrawn [a. p., fig. 8) ; 
and (if I mistake not) the investments of the puparial gills. 
The most noticeable feature, however, is the presence of the 
two main tracheary tubes {tr, tr, fig. 9), which appear to 
arise at either side from the anterior part of the pro-thorax. 
Doubtless by dissection the spiracles whence they arise would 
be found, and the true nature of the mass at the hinder part 
of the thorax could be ascertained by floating in water, but I 
am unwilling to sacrifice so perfect a specimen for the sake 
of these details, which may perhaps be obtained from other 
examples in the coming season. 
The larvse of Lepidoptera, in changing their skin, cast also 
the lining membrane of the great tracheal trunks ; it seems 
fair to infer, therefore, from the specimen now under con- 
sideration, that in the so-called pseud-imago condition of the 
Ephemeridse, we have merely the pellicle forming the inner 
investment of the pupa, carried out by the fully-formed insect 
in its first flight, and shortly got rid of. 
As a small contribution to the history of minute mark- 
ings,'''' which will some day, and that probably before long, 
have to be considered in its extended bearings, it may be 
mentioned that the tegument of the May flies is thickly 
covered with a minute elevated punctation. 
