AQUATIC INSECTS IX NEW YORK STATE 349 



respiratory filaments (blood gills). These are three branched, 

 sometimes simple, often much lobed [pl.3T, 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 placed 

 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 

 Kpun continuously down to the caudal end, where several 

 threads are drawn from thQ cocoon and attached to the last 

 one or two of the body segments of the pupa. The threads hold 



