166 CHIRONOMUS PRASINUS. 



stomach and intestine is very sharply marked both in the character 

 of their epitheUal and muscular coats, and the tubes here seem 

 decidedly to enter the lower portion of the stomach. It is 

 difficult to see how this comes about. 



Connected with the alimentary canal are two large glandular 

 sacs, which open by ringed ducts, uniting to form a common duct 

 which opens into the oesophagus immediately behind the mouth. 

 I have cursorily glanced at these organs both in Taiiypiis and the 

 Blow-Fly. In Chironomus they are specially worthy of attention. 

 Their high development may be estimated by the activity and 

 importance of their function, as evidenced by the felting of the 

 mud in which the insects live. This development does not lie in 

 the extent of secreting surface as brought about by the methods 

 usually adopted in the compound glands of vertebrates. Like 

 other glandular structures of insects, they are simple though 

 somewhat irregular in shape, and the reason of their extraordinary 

 efficiency as secreting organs must be sought rather in the 

 character of their secerning elements than in their multitude, and 

 these present under microscopical examination two special charac- 

 ters, that may both, I think, contribute to this result, viz., first the 

 character of the nucleus, and second the shape of the cell and 

 the position of the nucleus therein. Figure 4 represents a portion 

 of the gland in a condition, as I take it, of comparative functional 

 inactivity, a state, at all events, in which I sometimes find it. The 

 cells are of considerable size, as may be seen by the scale attached, 

 and are nucleated and slightly granular in aspect, but there is 

 noticing unusual in their appearance. On other occasions, how- 

 ever, the nuclei present a very peculiar aspect, which I have never 

 seen except in structures of these and allied larvae. As these 

 features of the nuclei have formed the subject of a paper by Prof. 

 Balliani, I prefer to give succinctly the result of his observations 

 thereon.* 



He commences by showing that structures similar to this had 

 been previously observed by him in other insects, etc., where the 

 nuclei presented granulations arranged linearly. To bring them 

 out he uses acetic or chromic acid for just sufficient time only to 

 produce the result; further action being injurious. By such 



* Carus Zool. Anzeiger, 1881, pp. 637 and 662. 



