GNATS 125 



(intestine). The mid-gut, or stomach, is formed differently, 

 by the completion into a tube of a pair of cellular bands 

 which immediately enclose the yolk. The fore-gut and hind- 

 gut, being formed by the pushing inwards of the outer skin, 

 possess a chitinous cuticle, internal to its generating layer. 

 The stomach, which has never formed part of the outer 

 integument, has no cuticle of its own. The sexual germ-cells 

 are by this time enclosed within the hinder end of the 

 body, where they appear as a pair of cellular masses; in a 

 later stage they give rise to the ovaries or testes. It is 

 remarkable that these are the very first parts of the body to 

 be differentiated. 



Stage 7. During the third day the jaws begin to take 

 their ultimate form. The dorsal wall of the body is com- 

 pleted by the growing upwards of the edges of the ventral 

 plate. 



Stage 8. During the fourth day the wall of the stomach 

 is completed. Eye-spots appear, and the dorsal vessel forms. 



Stage 9. The body is by this time (fifth day) longer than 

 the egg, and becomes coiled in consequence. On the sixth 

 day the coiling increases, and the larva begins to move about 

 within the egg. The egg-shell is burst open, and the larva 

 becomes free. It is now half a millimetre long, and differs 

 from the full-grown blood-worm in several particulars. The 

 blood has no red tinge ; there are no ventral blood-gills ; the 

 head is very large, and as yet encloses the brain. These 

 peculiarities are lost after the first moult. 



25. GNATS {Culex) 



The early stages of gnats are passed in water. They 

 require still water, such as is found in ponds, ditches, and 

 cisterns, and thrive best when it contains much microscopic 

 life. Hence foul water, or water containing abundance of 

 dead leaves, yields a suitable breeding-place for gnats of 

 several kinds. 



The larva floats at the surface of a pool in a nearly 

 upright position, the head downwards, and the tail-end in 

 communication with the air. If we examine it closely with 

 a lens in a good light, we see a gleaming band around the 



