CHIRONOMUS PRASINUS. 67 



obliteration of the tracheal system. A very few tracheal branches 

 are seen to ramify in the thoracic segments, and as the period of 

 pupation approaches these become more conspicuous ; but with 

 this exception, there is no appearance of a tracheal system. How, 

 then, is respiration effected ? Partly, it may be presumed, through 

 the general integument, but more particularly, undoubtedly, by 

 particular portions of that integument, which seem to be specially 

 differentiated for the purpose of supplying the deficiency of tra- 

 cheae, viz., the four finger-like processes which are appended to the 

 penultimate segment of the larva (see PL IX., Figs. 2 and 3), the 

 cuticle of which is more deficate than elsewhere, and, therefore, 

 well adapted for the purpose. Lastly, we may notice that the 

 antennae which in Tanypus are retractile are not so here, and there 

 is no reason to think that they act differently from the same organs 

 in other insects. 



Having thus pointed out the main outhnes of agreement with, 

 or divergence from, the subjects of preceding papers, I will now 

 proceed to give some details of structure and other observations 

 which seem to me of special interest, confining my remarks in the 

 present paper to the larval condition of the insect, and reserving 

 the pupa and imago stages, and also the tgg^ for a future oppor- 

 tunity. I may premise that these larvae are found abundantly 

 in muddy streams and brooks, in the mud of which they live, 

 and where they sometimes form rough, muddy tubes ; more 

 generally, however, these tubes are little more than tracks, con- 

 solidated by the secretion from the salivary glands, which is poured 

 out in such quantity as to form the substance of the mud into a 

 kind of consistent felt, traversed in all directions by their burrows. 

 In the vessel in which I keep them, this muddy felt can be lifted 

 out en masse with a pair of forceps, and the bottom of the brook 

 where I find them has a thick carpet of it, the presence of which 

 must materially modify the detrital action of the stream. 



To commence with the integument. This consists, as else- 

 where, of an external cuticle and an internal layer of hypoderm, 

 beneath which again there is, I think, a basement membrane. 

 These structures have been more or less observed in many Insects 

 and Crustacea by Leydig, Haeckel, Weissmann, Grueber, and lastly 



