OF CHLOËON (EPHEMERA) DIMIDIATUM. 483 
Proimago. 
One morning in June I observed a full-grown larva, which had a glistening appear- 
ance, owing to the presence of a film of air under the skin. I put it in my microscope, 
under a low power; and then, having added a drop more water with a pipette, J put the 
instrument down, and looked through the glass. To my astonishment, the insect was 
gone, and an empty skin only remained. I then caught a second specimen in a similar 
condition, and put it under the simple microscope, hoping to see it come out. Nor was 
I disappointed : very few moments had elapsed when I had the satisfaction of seeing the 
thorax open along the middle of the back; the two sides turned over, the proimago 
literally walked out of itself, unfolded its wings, and in an instant flew up to the window. 
Several times since, I have had the pleasure of witnessing this wonderful change ; and 
it is really extraordinary how rapidly it takes place; from the moment when the skin 
first eracks, not ten seconds are over before the insect has flown away. For some little 
while before the change the larva is rather helpless; but this is of the less importance, 
because this larva is not obliged, like many others, to leave the water before it emerges. 
Owing to the production of air between the old and new skins, it naturally comes to the 
surface; and it is probable that the quantity of air between the folds of the wings brings 
the baek of the thorax uppermost. When the larval skin has burst and folded itself 
back, it acts for the moment as a raft. 
The antennee-are as in Plate LVIII. fig. 2a & b; they consist of a basal portion formed 
by two segments, and succeeded by an unjointed whiplike part, which has a very curious 
appearance, the whole surface being covered by small but well-marked ridges, which 
indude small angular areas. Zaddach maintains that the antennæ of the imago are nof 
homologous with those of the larvæ ; but it is evident that in Ephemera, at least, there is 
no such difference. 
The pillared eyes of the male are brown, but each has a pale band running round it 
just below the erown. The three ocelli have not changed much in appearance. On the top 
of the head, between the two large eyes, the male has two rounded eminences, which 
occupy the places where two new eyes will, in the perfect imago, make their appearance. 
The feet of all the three pairs are similar (see Plate LIX. fig. 12, which represents the 
first pair). The tarsi are four-jointed ; the last bears a soft rounded pad, which might 
be described as a fifth tarsal segment. In the two posterior pairs of legs, the third tarsal 
“gment is shorter than the others. The claw is quite small, and does not project beyond 
the termina] pad. There are no long hairs on the legs, which are covered, however, by 
Short ones; those on the tarsus are stiff, and almost deserve the name of spines. The 
Skin of the tarsal segments is thrown into small ridges like those on the antenne. | 
alo e wings are of a dusky hue. They are covered by minute hairs, a ar ue 
"i s hinder edge (Plate LIX. fig. 13). This appears to be the case also wi : 
» of the other species of the group. 
The caudal filaments are about ian inch in length; near the base they are 130 a 
an in = d, where they are only soo: 
ch in thickness : but the the free en 
; ; y gradually taper to the ferte 
se finally in a blunt tint: The segments at the base are about 135 of an inch in 
"sth, but they increase somewhat towards the free end. There are no longer any 
