THE MALARIAL MOSQUITO 119 



If in groups or rafts they are of the Culex. 



If singly they are of the Anopheles. 



Each Qgg is oval, one end blunter than the other, with a pigmented 

 chitinous shell. It has a very fine external membrane which facilitates 

 the floating of the eggs. 



They hatch in twenty-four hours in a hot tropical season. 



Larvce. — All must live in water and can be found in collections 

 almost anywhere, even in sea water, but not as a rule in rivers where 

 the current is strong. They are very active, and live principally on 

 algag and similar vegetable matter. 



The head is a rounded chitinous capsule with well-developed 

 appendages. 



The eyes are irregular masses of pigment in the younger, and 

 distinctly faceted in the older ones. 



The antennae are long. 



The clypeus is prominent, to which are attached the " mouth- 

 brushes," which have a rotatory motion to sweep food to the mouth. 



The thorax has three segments, distinguished from the abdomen 

 only by an arrangement of hairs, which are in tufts, single-branched 

 or feathered. 



The abdomen is elongate, soft, with nine segments sometimes beset 

 with stiff hairs like the woolly-bear caterpillar, but usually hairs are 

 lateral and on the free edge of the last segment. On the dorsum of 

 the eighth segment the breathing organs open by two independent 

 orifices in Anopheles, or one breathing tube of varying length in others. 

 This latter has a valve and carries spines. 



The intestine opens at the free end of the ninth segment, which 

 carries bunches or whisks of hairs and four tapering tracheal gills. 



In repose some larvae hang with the head downwards with the tip 

 of the breathing tube at the surface for air, but the larva? of the 

 Anopheles groups lie horizontally to the surface. 



Larvas become fully grown in about one week, but in cold climates 

 may remain unchanged during the winter. 



They moult several times and feed continuously. 



Pupa. — They must live in water. 



They are active, but do not feed. 



In appearance thev are like tiny lobsters. 



The head and thorax form one mass. 



Two ear-like breathing trumpets come from the back of the head 

 mass for breathing. 



The curved abdominal ninth segment ends in a pair of large blade- 

 like fins. 



On the first segment there are two tufts of hairs, fan-like, to catch 



