The Examination of Larvce. 



cast larval skins. These skins are very transparent, but they can 

 be seen without difficulty floating near the surface of the vessel of 

 water in which the larvae are kept. Dr. Cogill recommends that 

 the larval skin, after having been transferred to a glass slide, should 

 be allowed to dry thoroughly and then mounted in thin Canada 

 balsam beneath a cover glass. 



It is of great advantage to be able to identify the different 

 species of " anopheles " by an examination of their larvae alone, 

 without the necessity of breeding out the larvae into adults. Grassi 

 was the first to show that this could be done for some of the 

 Italian species, and recent work by the members of the Royal 

 Society's Malaria Commission in India has shown that the majority 

 of the known Indian species can also be differentiated in the larval 

 stage of their existence. 



The structures by which the larvae of different species of 

 " anopheles " may be identified are as follow : 



(L) The Frontal or Clypeal hairs (PL IV, A & C). These 

 are four fine hairs which project from the dorsal surface of the 

 anterior end of the head. They may be called the external and 

 the median frontal hairs. The external hairs are placed one at 

 each corner of the dorsal chitinous end of the head, and exactly 

 overhang the prominent so-called whorl organs or " shaving 

 brushes." When the whorl organs are pushed out, the external 

 (corner) hairs are difficult to see, but when the whorl organs are 

 drawn in, they stand out prominently. The median hairs arise 

 close together near the middle line and project forward in front of 

 the head. They are easily seen under a ^ or ^ inch objective. 



A very important difference between the larvae of different 

 species depends upon the fact that the characters of these external 

 and median frontal hairs differ in different species. The details of these 

 differences are given under the descriptions of the several species. 



(2) The Palmate hairs (PL IV, A & B). If the dorsal 

 surface of the abdomen of an " anopheles " larva is examined 

 under the microscope, a pair of little fan -shaped organs will be 

 seen on the majority of the segments. These are the so-called 

 "Palmate hairs." Each consists of a short stalk surmounted by a 

 bundle of about 15 to 18 hairs which are arranged round the stalk 

 like the petals of a flower. When the larva comes to the surface 



[35 



