SKIN-BOAT OF THE GNAT. 11 



are enclosed in crackers, and have to be worn by those who 

 draw them. 



In process of time the pupa changes to a perfect Gnat within 

 this shelly case, able to move, but unable to eat. The body 

 shrinks in size, and the wings and legs are formed, both being 

 pressed closely to the body. When the Gnat is fully developed, 

 the pupal skin splits along the back, and opens out into a 

 curiously boat-like shape, the front, which contains the heavier 

 part of the insect, being much the largest, and consequently 

 being able to bear the greatest weight. 



By degrees, the Gnat draws itself out of the split pupal skin, 

 resting its legs on it as fast as they are released. It then 

 shakes out its wings to dry, and finally takes to the air. 



It is a really wonderful fact that the insect which, for three 

 stages in life namely, an egg, larva, and pupa lived in the 

 water, should in the fourth not only be incapable of aquatic 

 life, but should employ its old skin to protect it from that very 

 element in which it was living only a minute or two before. 



Should the reader wish to examine for himself either the egg 

 or skin boat of the Gnat, he can easily procure them by search- 

 ing any quiet pond, or even an uncovered water-butt. They 

 are, of course, very small, averaging about the tenth of an 

 inch in length, and are nearly always to be found close to the 

 side either of pond or tub, being drawn there by the power of 

 attraction. 



I may here mention that there are other dipterous insects 

 belonging to the genus Stratiomys, which undergo their meta- 

 morphosis in a very similar fashion. In these insects, the 

 larva breathes through the tail, and when it attains its pupal 

 condition, the actual insect is very much smaller than the 

 pupal skin, only occupying the anterior and enlarged part. 

 Indeed, the difference of size is so great, that several entomo- 

 logists believed the future Stratiomys to be but a parasite on the 

 original larva. The beautiful Chameleon-fly (Stratiomys cha- 

 mceleori) is a familiar example of these insects. 



