254 THE AMERICAN MONTHLY [Sep 
fly, besides the mouth parts and other organs of the head. 
Each appendage has its own sheath, part of the proper 
pupal skin, and the appendages are cemented together 
by some substance which is dissolved or softened by al- 
cohol. At the tail] end is a pair of flaps which form an 
efficient swimming fan. The body of the pupa, like that 
of the larva, is abundantly supplied with air-tubes, and 
a communication with the outer air is still maintained, 
though in an entirely different way. The air-tubes no 
longer open towards the head. Just behind the heart of 
the future fly is a pair of trumpets, so placed that in a 
position of rest the margins of the trumpets come flush 
with the surface of the water. Floating in this position 
the pupa remains so long as it is undisturbed; but if at- 
tacked by any of the predatory animals which abound in 
the fresh water it is able to descend by the powerful 
swimming movements of its tail.”” Then follows an ex- 
planation, too long to quote, as to why the respiratory 
organs are changed from the tail end in the larva to the 
head end in the pupa. “But a time comes when the fly 
has to escape from the pupa-case. The skin splits along 
the back of the thorax, and here the fly emerges, extri- 
cating its legs, wings, head, and abdomen from their 
closely-fitting envelope.” “The mouth of the female 
gnat is provided with a case of instruments for piercing 
the skin and drawing blood. The foremost of these isa 
tube split along its hinder side, which lies in front of the 
rest, and is used in suction. This, though long and slen- 
der, is stouter than the delicate parts behind it, and it 
serves to stiffen and protect them; then come fine, long, 
and slender blades of great delicacy. Two pairs corres- 
pond to the mandibles and maxille of other insects, 
though here they are so simplified and attenuated that it 
is not easy to make out the correspondence. The maxil- 
le are furnished near their tips with a row of extremely 
miuute saw-teeth. There is also a fifth unpaired imple- 
