522 



Mr. T. H. Taylor's Note on the 



larval clvvelliDg. The last thing the 

 larva does before pupation is to make 

 a new aperture at the fixed end, 

 which may be distinguished as the 

 front opening. This aperture is 

 seldom single ; generally two, three 

 or even four sninll circular holes are 

 arranged in a r'nvf around the attach- 

 ment of the stalk. The advantage of 

 several small holes over one large one 

 is obvious; they do not weaken the 

 strand so much, nor are they so 

 liable to be torn by the force of the 

 stream. When all is ready the larva 

 pupates; the old larval skin is usually 

 allowed to float out of the tube, for it 

 is seldom seen afterwards. 



The pupa of this species of Chirono- 

 mus has minute prothoracic horns in 

 which no apertures are visible, and 

 an effective tail-fin. It lies in the 

 chamber with its head towards the 

 attached end, that is, pointing up- 

 stream. It maintains an undulatory 

 movement with its body, Avhich causes 

 water to be drawn in at the front 

 opening and passed out behind. As 

 the front opening looks up-stream 

 and the hinder down-stream, it follows 

 that the course of the respiratory cur- 

 rent is parallel to and in the same 

 direction as the flow of the stream. 

 "When, in the course of a few days, 

 the fly is ready to emerge, the pupa, 

 by means of the hooks on its body, 

 forces a way through the front open- 

 ing. It then rises to the surface of 

 the water, when the skin at once 

 splits open along the back and allows 

 the fly to escape. 



It frequently happens that while 

 the pupa is still within its case, the 

 six-legged larva of a water-mite is 

 found attached to its body, geiierally 

 on the upper part of the thorax. 



<*e?-7'"'.-'-' 



m. 





mill 



r-*.v:/,v.",; -.;:;<:¥ 



r.J-n. 



Vrr.-:n 





Fig. 1. Larval tube of 



Chironomus ( Orth ocJa- 



dius) sordiddhis x 8. 



