i8 AGRICULTURAL EXPERIMENT STATION. 



segments. On the eighth of these segments is a tube or siphon 

 of variable length and through this the insect breathes. As it 

 usually gets its air supply from above the water surface its 

 natural position is head down and tail up. It has no legs or other 

 organs of locomotion and moves by a series of jerks or wriggles 

 which drive it rapidly downward or irregularly away from the 

 point of disturbance. 



Figure 2 on page 19 is a diagrammatic representation of a 

 Culex larva, ancl this will serve very well for a type of all save 

 the few species of Anopheles and Corethra group. The parts 

 shown there are all of more or less importance in classification 

 and need either a good hand lens or a compound microscope for 

 their discrimination. 



The head is usually wider than the body segments and nar*- 

 rower than those of the thorax ; but this varies in each direction, 

 the head in some forms being the widest portion of the larva. 

 It may be either lighter or darker in color than the body and may 

 be uniform or maculate. When maculate, the markings are very 

 constant and form a reliable basis for the recognition of the 

 species. At the sides of the head, the eyes are the most prom- 

 inent organs; usually blackish and so much alike in the species 

 as to be unavailable for classification. 



Nearer to the front of the head are the antennas — one on each 

 side — and these may be long or short, straight ot curved, and if 

 cuiTed, it may be to the out or to the inside, or there may even 

 be a double curve; they may, be of equal thickness throughout, 

 or there may be a thickening at base, with an abrupt narrowing 

 at or near the midde, forming a set-off. At or about this place 

 there is usually also a tuft of hair, which may be dense or thin, 

 long or short. These^ features are of great importance in clas- 

 sification and some species are recognizable at once by the form 

 of the antenna alone. At the tip there is usually a very small 

 articulated joint or process and a number of longer or shorter 

 spines and hair. 



When we watch a wriggler closely we find that the mouth 

 structures are in constant i motion and that, apparently, there is a 

 pair of brushes composed of long, fine hair. These mouth 

 brushes seen under the microscope are excellent devices for gath- 

 ering in the minute organisms upon which the larvae feed ; some- 

 times the hair in the brushes is all simple, sometimes some of it 

 is pectinated or toothed like a comb, so that, however- minute 

 the creature, it may be drawn in. These brushes form part of 

 the maxillary structure of the mouth. Just above them are the 

 minute mandibles or jaws, with their complicated teeth and 

 edges adapted for tearing and crushing, for the ordinary wriggler 



