172 CHIRONOMUS PRASINUS. 



each side of the head, serve the purpose, it may be presumed, of 

 eyes ; each of the inner pair is furnished with what looks like a 

 couple of crystalline lenses. The antennae are bifid, as shown 

 in Figs. 9, 13, and 14. 



Muscular System. — I have little to say at present on this 

 subject beyond what I have mentioned in connection with the ali- 

 mentary canal. There is the usual muscular intestine lying under 

 the. integument (see Fig. 3), and consisting principally of longitu- 

 dinal fibres, connecting segment with segment. They are broad, 

 band-like, striated fibres of somewhat equal diameter throughout, 

 attached by either extremity to the integument, and invested with 

 sarcolemma. By their means the various movements of the body 

 are produced, and special fibres are found in the head connected 

 with the organs of the mouth. Transverse muscles also occur 

 in the abdominal segments, which in the living larva frequently 

 stand out from the surrounding tissues with an opalescent 

 brilliancy. This happens whenever the axis of the fibre corres- 

 ponds with the line of vision as is frequently the case during the 

 movements of the animal. They are thus represented in optical 

 section in Fig. 21, and their position is indicated in Fig. 2. One 

 observation I should like to make with reference to the phe- 

 nomenon of contractility evinced by them. If a living larva be 

 crushed under the cover-glass while under observation, so as to 

 press out the viscera, etc., and yet not disintegrate the muscular 

 coats, the muscles will be seen for some time to exhibit irregular 

 contractions, as follows : — One end of the muscle suddenly 

 assumes a great increase in breadth, and the transverse striae 

 become approximated. This swollen portion passes like a wave, 

 with more or less activity, to the other end, so that the whole of 

 the muscle does not become contracted at once, but every 

 portion of it swells and contracts successively ; another wave 

 following the first after an interval. This is an example under 

 exceptional conditions of the normal mode in which muscular 

 fibres contract, and affords a very instructive lesson. 



