MOSQUITO DIAGNOSIS. 



249 



second posterior cell"; or "the base of the first submarginal 

 cell is almost level with that of the second posterior." 



I therefore suggest that a line be drawn through the angles 

 of the two cells in question and produced to cross the cost a. The 

 basal angle which this line makes with the costa can be used as a 

 critical angle for the fork-cells of each species. The size of the 

 angle can be quite reasonably gauged by mere observation, or 

 can be accurately measured from a camera lucida drawing or micro- 

 photograph. 



Fig. 2. — Critical angles for fork-cells. 



Palps. 



The position and size of bands of anopheline palps or culicine 

 probosces are of diagnostic importance. Diagrammatic representa- 

 tions are frequently misleading. I suggest therefore thai a definite 

 numerical palp formula be assigned to each anopheline. 



The idea is, always to divide the palp into 24 imaginary divisions. 

 The relative proportions of dark or light segments are expressed 

 by a simple sequence of numbers beginning from the base of the 

 palp, dark sections being shown by ordinary numerals and lighl 

 coloured sections by italic numerals. The number, size and poail inn 

 of the bands is thus seen at a glance, and palps «>f differenl species 

 can be compared without the expense of reproduced drawings 

 and without the indefiniteness of a written description. 



