AQUATIO INSECTS IN NEW YORK STATE 349 
respiratory filaments (blood gills). These are three branched, 
sometimes simple, often much lobed [pl.37, fig.9]. Caudad of 
- these is a chitinized, X-shaped fold, the anterior branches ex- 
tending cephalad and laterad for a short distance. At the 
caudal end, with its plane nearly at right angles to the longitu- 
dinal axis of the body, are concentric circles of tiny hooks, the 
center of the circle being hollowed out, suckerlike. The rows 
of hooks, though arranged in concentric circles, are also ar- 
ranged radially, so that about 100 radii may be counted, each 
radius with from eight to 20 hooks (varying with the species, 
and perhaps also, with the age). The function of these hooks 
with the suckerlike disk is for attaching the larva to the rock 
or rubbish in the water, affording a very firm hold. In some 
species the circle is not quite complete, but is slightly open on 
the dorsal side. The-larva possesses two silk glands, laterally 
placed, extending about three fourths the length of the body, 
then recurved, U-shaped, extending back to the thoracic seg- 
ments. The outlets are the two ducts which lead into the 
hypopharynx [pl.37, fig.2]. The silk is used by the larva for 
attaching itself to the surface on which it rests, to prevent 
its being washed away by the rapid flowing water and to build 
its pupal case. According to observations made by Miss 
Phillips and recorded in her thesis (1890), the spinning of the 
cocoon of S. pictipes is described as follows: 
“In spinning, the thread issues from the mouth and is piaced 
in the different positions by the thoracic proleg. The head is 
bent down, and with the proleg the thread is drawn around the 
body and other threads placed or twisted in all directions, until 
a very irregular network is formed, covering the whole of the 
body, except the head. The skin of the head is then cast off, 
and the insect pulls itself out of the skin of the body, leaving 
it whole. The cast skin may often be found in the cocoon, with 
the pupa. The cocoons are commenced at the upper margin and 
spun continuously down to the caudal end, where several 
threads are drawn from the cocoon and attached to the last 
one or two of the body segments of the pupa. The threads hold 
