The dorsal tubercle is larger than the lateral ones and is often pointed; 

 the lateral tubercles are blunt. The apex of the tubercles is retractile, 

 forming a longitudinal fold in the case of the dorsal tubercle or a trans- 

 verse fold in the case of the lateral tubercles. In the Limnophilidae, also 

 the ventral surface of the 1st abdominal segment often bears a ridgelike 

 tubercle. In larvae of Integripalpia living in tubes, the pleural region of the 

 abdomen bears a so-called lateral line which is a fine fold covered with 

 short hairs; the function of this line is to increase the water current in the 

 tube when the abdomen makes undulating movements. 



The 9th segment is narrower than the others; it bears the slitlike anus 

 posteriorly; the sides of this segment bear the short posterior or anal legs 

 (postpedes) which end in claws. 



The sclerotization of the abdominal segments is little developed, in the 

 form of small sclerites and sclerotized dots; it is usually present only on 

 the anterior and posterior parts of the abdomen. In a number of families 

 of Annulipalpia (Philopotamidae, Stenopsychidae, Psychomyiidae, Ecnomidae, 

 26 Polycentropodidae) the abdomen of the larva is not sclerotized at all;* in 

 Rhyacophilidae, Glossosomatidae and Hydroptilidae the sclerite of segment 9 

 covers almost the whole dorsum of the segment; in the Hydroptilidae, small 

 tergites are often present also on the other abdominal segments; these 

 sclerites are distinct; they are also well marked in larvae of St act obi a, 

 young larvae of Ag r ay le a, and larvae of the American species of Leuco- 

 t r i chi a (Ross, 1944:120, Figure 449), in the larvae of the genera Plethu s 

 and Lamonganotrichia (related to St a c t ob i a) described by Ulmer 

 from the Sunda Islands, and in some other forms (Ulmer, 1957:180, 195, 

 202-203, Figures 94-99, 114-118). Nielsen described small (almost 

 rudimentary) tergites on young larvae of Hydroptila and Oxyethira 

 (Nielsen, 1948:94, 92). In the Integripalpia, the sclerotization of the 1st 

 abdominal segment (Limnophilidae) consists of small sclerites or dots 

 near the dorsal and lateral tubercles, and on the ventral ridge which some- 

 times bears a well-marked sternite in the middle. In the Molannidae and 

 some Limnophilidae, there are small sclerotized dots instead of the lateral 

 line or near it. The dorsal sclerite of segment 9 (if present) is variously 

 developed, covering the dorsal surface of the segment completely or nearly 

 completely, or occupying only a small part of it (Figures 11 and 12). 



(27) 



FIGURES 11 and 12. Dorsal sclerite of the 9th segment: 



11 - Rhyacophila subovata; 12 — Od ontocerum albicorne. 



Except the anal legs which are described below. 



22 



