82 



Note differences in naked eye appearance ; 

 note the long worm-like Stegomyia larva and its 

 wriggling mode of progression ; note the trans- 

 parent and spiny appearance of some larvae 

 (notably Taeniorhynchiis) ; note that some larvae 

 adopt a nearly horizontal attitude (C. concolor and 

 others), others a vertical attitude (S^^owyja),whilst 

 the majority form a small angle with the vertical. 

 Examine larvae under a low objective. Note the 

 head with eyes, large feeding brushes, antennae and 

 various hairs ; note the large bunches of hairs 

 arising from the thorax and abdominal segments ; 

 note the last segment bearing four large clear 

 papillae and two systems of hairs ; note the penul- 

 timate segment which carries the syphon tube and 

 some curious claw-like spines. 



Note especially the following : — 

 (i) The syphon tube, 

 (ii) The antennae. 

 (iii) The mouth parts. 

 (ivl The anal papillae. 

 (v) The hairs of the thorax and abdomen. 



The Syphon Tube. — This is formed of a single 

 cylindrical piece of chitin, and contains the origin 

 of the two main tracheae of the body. Note the 

 small flap-like pieces of chitin forming a closing 

 apparatus at the extreme tip. Measure (by eye- 

 piece micrometer) the length and greatest breadth 

 of the syphon tube ; note that in different species, 

 and especially in different genera, the syphon tube 

 varies greatly in its measurement. By dividing 

 the length by the breadth a figure may be obtained 

 which is useful, and may be termed the syphonic 

 index number ; note that in Stegomyia this 

 number is about two. In Culex, four to seven. In 



