Tue CrANE-Fuies oF New York — Part II 801 
of the black fly (Simuliidae). Both larvae and pupae spend their entire 
lives in cases on stones in water — usually in running, well-aérated water, 
and often in the most rushing torrents. 
The larvae, as already stated, lack spiracles, the entire respiration being 
carried on thru tracheal gills, four in number, and the rich tracheal 
development in the elongate caudal lobes. Thus the tracheal system is 
truly closed, and represents the maximum of specialization in the reduc- 
tion in size and final loss of the spiracles. In air-breathing, terrestrial 
forms, the spiracles are large and situated comparatively close together, 
gradually becoming smaller and more removed from one another as the 
creature becomes more and more dependent on blood gills or tracheal 
gills for respiration. This is the only truly closed tracheal system known 
to the writer to occur in the Tipulidae. It should be noted that the loss 
of the spiracles is accompanied by great enlargement of the gills and the 
taking on of the gill function by the two caudal lobes. The haunt of the 
larvae is in silken cases on rocks, often in the swiftest part of the stream, 
where it is impossible to breathe thru spiracles and where the associated 
forms of life (Kphemerida, Plecoptera, Trichoptera, and Diptera) all, 
or practically all, depend entirely on gills for respiration. 
As a rule, the larval cases are made on rubble or rounded stones, a 
crevice or a groove caused by inequalities of the rock surface covered 
over being the simplest and commonest place chosen. The inequalities 
in the rock are bridged over by a silken, mud- or silt-covered case, which 
is very delicate and laterally fimbriated with the young larva but becomes 
much firmer, thicker, and more compact with the older larva and 
pupa. The larval case is open at both ends and the larva passes back- 
ward and forward freely, showing considerable agility when disturbed. 
When the larva is still small, the case is correspondingly small and 
insignificant; but the case of the matured larva is conspicuous, measur- 
ing from 4 to 5 centimeters in length and about 1.2 centimeters across 
the lateral “ wings,” or fimbriations. The insect moves freely along 
the tube but is very loath to leave it unless actually ejected. As 
stated above, the late larval and pupal covering is very different from the 
flimsy, silt-covered tube of the young larva, being smooth, compact, 
hard, and often covered with pebbles. The pupa has two powerful hooks 
at its caudal end, enabling it to fasten to the case. In most cases the pupa 
hangs with the current, head downstream, like the pupa of Blepharocera 
