THE BOOK OF NATURE STUDY 



the margin of the water, and, when in vessels, are generally to 

 be found close to the sides. 



At the close of pupal life the animal usually swims away 

 from the side into open water, and at once straightens out the 

 abdomen so as to bring it horizontal and flush with the surface. 



The skin of the thorax then 

 splits open dorsally, and 

 the thorax, head, legs, and 

 wings of the adult gnat are 

 lifted clear of the husk, and 

 at length with the with- 

 drawal of the abdomen the 

 whole animal is free. The 

 empty pupal husk now 

 serves as a raft upon which 

 the imago stands while the 

 wings enlarge a little and 

 dry. In a few minutes the 

 gnat flies away. The whole 

 process from the time when 

 the pupa strikes out away 

 from the edge until the 

 imago takes wing occupies 

 under five minutes. The 

 exact duration of each stage 

 is subject to much fluctua- 

 tion ; e.g. a batch of eggs 

 obtained by the writer in 

 the middle of September 

 1906 yielded a number of 

 larvae some of which passed 

 right through to the imago 

 by the end of October, 



while others of the same family were still larvae in the third 

 week of November. 



The adult gnats may be kept alive in captivity if fed on slices 

 of banana or other fruits whose juices they can suck. It is pro- 

 bable that vegetable fluids, rather than animal blood, are their 



FIG. 13. Imago of culex emerging from pupa 

 skin. (After Miall.) 



