242 THE MOSQUITOES. 



There is a pair of wings attached to the posterior part of the 

 mesothorax and, more posteriorly still, a pair of rudimentary wings 

 (halteres) attached to the metanotum. The 3 pairs of legs are at- 

 tached to the thorax. 



There are 9 segments in the abdomen. The genitalia arise from 

 the terminal segment as bilobed processes. In the male there is a pair 

 of hook-like appendages or claspers, between which, and ventrally 

 situated, are the harpes, also a pair of chitinous processes. 



In considering the question of the possible danger which might 

 arise from the introduction of a case of yellow fever, malaria or filariasis, 

 it would give the greatest information if the ova were at hand so that we 

 could by watching the development from egg to larva, pupa and insect, 

 have all the points from which to decide as to the genera developing in 

 the given locality. It is generally a very easy matter to dip out large 

 numbers of larvae from the pools and having noted the characteristics 

 of the larvae, to do the same when the pupae develop; so that we have 

 only to verify our identification when the insect emerges from the pupa. 



THE OVA. 



The egg raft of Culex, containing about 250 ova, is quite perceptible 

 on the surface of the water as a black, scooped-out mass, about 1/5 of an 

 inch in length. The eggs are set vertically in the raft. The eggs of 

 the Stegomyia are laid singly and have a pearl-necklace-like fringe 

 around them. 



The Anophelinae eggs are oval in shape with air-cell projections 

 from either side. They are laid in triangle and ribbon patterns. The 

 markings of these air cells vary and have been used for differentiation. 

 The length of time of the egg stage varies according to temperature 

 and other conditions i to 3 days for Stegomyia and 2 to 4 days for 

 Anophelinae. The Anophelinae are more difficult to raise than 

 Culex or Stegomyia. 



LARV.E. 



There are two great classes of larvae the siphonate and the 

 asiphonate. The latter are always Anophelinae. 



The Culicinae larvae have a projecting breathing tube at the 



