the whole dorsal vessel forms a thin-walled, light tube; in a young, freshly- 

 molted larva, the pulsation of the dorsal vessel is visible through the trans- 

 parent wall of the body. The first four pairs of alar muscles of the dorsal 

 diaphragm are smaller than the following five pairs; the alar muscles are 

 connected anteriorly and posteriorly. The hemolymph is colorless and 

 light; the protein content of the plasma is low (1.3 — 2.6% in the larvae of 

 Limnophilus, according to Kuznetsov, 1948:184); its reaction is very 

 constant and resistant to changes of the pH of the environment; in species 

 kept in an alkaline medium (pH 7.60—8.08) or in an acid medium 

 (pH 3.0— 6.55), the pH of the hemolymph remained almost unchanged. 



With age, the reaction changes (the pH decreases); for example, in larvae 

 of L. flavicornis the pH of the hemolymph decreased from 7.18 to 

 7.05 during the hot months of the year when the larva grew rapidly (Krey, 

 1937:203-207). 



The fat body of the larva consists of small milk-white lobes; toward the 

 end of the larval life, in the prepupa, the fat body reaches its maximum 

 development and becomes darker. 





pH of the medium 





alkaline 



acid 



Phryganea striata 



6.73-6.78 



6.98 



6.99 



6.94 



6.87 



6.71-6.81 





6.80 





7.02 



Anabolia nervosa 



6.96-7.00 



Halesus digitatus 



6.94 







Tracheal system. The larvae of Trichoptera have a closed 

 tracheal system; they obtain the necessary oxygen from water, by tracheal 

 gills or through the integument. The main respiratory storage unit is 

 two longitudinal lateral trunks (trachea lateralis) extending from the 

 41 prothorax to the 9th abdominal segment (Figures 40 and 4l); these vessels 

 are thickest in the thorax; their diameter is 0.12 mm in Rhyacophila 

 septentrionis; the lateral vessels taper gradually toward the posterior 

 end of the body and in the last abdominal segment they form thin stems 

 branching in the anal legs into a network of tracheae and tracheoles. In 

 the prothorax, each of the lateral tracheal stems divides into two branches 

 inside the head (Figure 42), the dorsal and ventral tracheae (trachea 

 cephalica dorsalis and trachea cephalica ventralis); the dorsal branch 

 supplies the musculature and nervous system of the dorsal part of the head, 

 including the supraesophageal ganglion, the ventral branch, the ventral and 

 preoral regions of the head, including the subesophageal ganglion and the 

 mouthparts (trachea mandibularis, trachea maxillaris, trachea labialis; 

 Novak, 1952:251-258). 



The lateral tracheal trunks in the thoracic and abdominal segments have 

 branches into the legs, the tracheal gills and internal organs, and especially 

 to the ganglia of the abdominal chord and to the intestine (Figure 43). 



Silk glands and Gilson's glands. The silk glands of the larvae 

 are two long tubes bent twice or more, situated at the sides of the body, 

 ventral to the intestine; they reach the 6th or 7th abdominal segment 



35 



