IO 



Bifurcating Hairs. 



Distribution 

 of hairs. 



Anal Sets:. 



Anal bristles. 



anterior appendages, but the anal appendages vary considerably ; for 

 instance in No. 17 (Appendix) there are twelve large almost black 

 hooks slightly separated into two groups ; these can be completely 

 retracted into the rather long foot, which is in like manner almost 

 folded into the body. Segments 5-9 bear each a pair of fringed 

 bifurcating hairs (Figs. \e and tod) attached laterally, one on each 

 side, near the posterior border of its segment. I have not been able 

 to detect any nerve terminating in these hairs, yet, as will be shown 

 later, they have probably a very important function to perform, and 

 must be delicate sensory organs. They are also important for classifi- 

 catory purposes. I have found five different species bearing these 

 organs, DR. LAUTERBORN mentions two, and PROF. MIALL informs me 

 that he has had one, hence we may safely conclude that these larvae 

 form a distinct group. I have called this the " Pusio " group, and 

 given a list of the known species in the Appendix. 



The head bears numerous stiff hairs arising from the centre of 

 circular pits surrounded by chitinous rings. Similar hairs are found 

 on the thoracic segments, about sixteen dorsal and ten smaller ventral 

 on the first, and a diminishing number on the other two. The ab- 

 dominal segments have only occasional, very minute, non-pitted hairs. 



On the dorsal surface of segment 12 are two bunches of long 

 stiff setae the anal setae. Each bunch is composed of 8 setae which 

 are chitinous at the base, becoming transparent towards the free ends. 

 The bunch takes its origin in a short transparent prominence, bearing 

 two small hairs at the base. In some species this prominence is of 

 considerable length and in others the cuticle is deeply chitinous, while 

 the setae may vary in number from one to about ten. 



Between the setae and the anus there is a small area characterized 

 by the presence of two small hairs, the anal bristles ; this area possibly 

 represents the dorsal part of a now rudimentary i3th segment. I 

 have found three species of Chironomus in which a i3th segment is 

 quite obvious, Nos. 8, 10 and n (Appendix). In one of these (No. n) 

 the segment is quite perfect. MIALL and TAYLOR* have also found 

 a Chironomus larva "with faint indications of a sub-division of the 



* MIALL and TAYLOR. " The Holly Fly " p. 260. 



