MAY FLIES AND MIDGES OF NEW YORK 123 



The mandibles are rather broad at the base, considerably curved 

 and prolonged into a long- apical tooth, the mesal teeth being short 

 and sometimes indistinct or wanting. The maxilla consists of a 

 broad, more or less square, fleshy process, with hairs or filaments 

 projecting cephalad and mesad (pl.19, fig.l mx.), and a prominent 

 palpus (p) with a short basal joint. The palpus is provided with 

 several papillae or apical processes. 



The hypopharyux consists either of a horseshoe-shaped piece 

 having a toothed margin (pi. 20, figs. Hi and Oh), excepting the mid- 

 dle section, or of two curved pectinate pieces, their tips nearly 

 touching each other; besides this there is a pointed slender lobe 

 (figs.lx and 6x) on each side of the labium. The laibium usually 

 has five, though sometimes ibut four, marginal teeth, differing 

 slightly in shape in the different species. The thorax is some- 

 what larger in diameter than the abdominal segments, and its 

 three segments not so sharply separated. The anterior prolegs 

 are quite long and slender. They have a long common base, and two 

 branches, at the ends of which protrude the retractile claws. 

 These claws are comparatively few r in number, quite distinct, and 

 not hair-like like those of Chiro nonius. The abdomen has 

 nine segments and is in some species provided with lateral cilia. 

 To the last segment of the abdomen are attached the abdominal 

 legs and appendages (pl.19, fig.10). On the dorsal surface, and 

 attached to the posterior margin of the ninth segment, are two 

 moderately slender cylindrical processes, about three times as 

 long as wide, each with a crown of six or eight long setae at the 

 tip; between the posterior legs is a pair of pointed blood gills (b), 

 and immediately dorsad of this pair is another pair. Often also 

 there is a pair of long setae dorsad of the upper pair of blood 

 gills. The anal feet are long and stilt-like, Degeer comparing them 

 to wooden legs. The claws are slender, each usually with a basal 

 tooth (pl.19, figs. 11 and 12), and are retractile. Blood worms 

 are greedily devoured by Tanypus larvae. The alimentary 

 canal has a reddish tinge, which suggests that the larva preys 

 upon the small red worms known as T u b i pex or some other 

 small creature which contains haemoglobin in its blood. Crus- 

 tacea actually have been seen alive in the alimentary canal. The 

 trachea 1 system is better developed than in C h i r o n o m u s 



