38o 



TEXT-BOOK OF ZOOLOGY 



01 Uk. Ok F Ul 



same order can resemble each other. (Describe the insect.) The female 

 is a "blood-sucking" creature; the male, since it does not lay eggs, 

 and therefore does not require so nutritious a food, is satisfied with the 

 sweet juices of plants. An insect living on blood must, however, possess 

 instruments for tapping this special juice. These are formed by the 

 two mandibles and maxillae, which are transformed into small daggers 

 (to which is added a fifth bristle formed from a prolongation of the 

 labium). These parts lie within the proboscis, which (exactly as in the 

 house fly) is formed by the long, gutter-shaped labium and the labrum 

 roofing in the gutter above. After pressing the pro- 

 boscis against the skin of its victim, it pushes in the 

 daggers and at once begins to suck the blood from the 

 wound. (The mouth parts of the blood-sucking fly 

 species are essentially constructed on the same plan. 

 How does the bee sting, on the other hand? Am- 

 monia alleviates the bite of gnats.) 



Gnats are most numerous in well-watered districts, 

 their youth being passed in ponds and pools. The 

 larva are legless creatures, provided on their sides with 

 long, swimming hairs, and progressing by undulatory 

 movements of the body. They are mostly seen hang- 

 ing to the surface of the water, and at the same time 

 spreading out a star or rosette of fine waterproof hairs. 

 In the middle of this rosette lies the opening of the 

 respiratory tube, which is capable of being closed ," 

 hence these creatures breathe the air outside of the 

 water. (Compare with larvae of water beetle.) 



The pupa also live in the water. They are mostly 

 seen with their body bent into the shape of a sign of 

 interrogation (?), hanging to the surface of the water 

 by two horn- or ear-like appendages of the head, in 

 which the respiratory tubes terminate. Thus, in consequence of the 

 position of these appendages, the head is directed upwards. At the 

 slightest shock or disturbance they sink below the surface. They swim 

 by the help of their long, movable abdomen, which is sharply marked 

 off from the thick, anterior portion (head and thorax) of the body. In 

 no other insect family do we find pupa endowed with so much mobility 

 and (in connection therewith) of such shape. In the case of the gnats, 

 however, these peculiarities are indispensable owing to their free existence 

 in the water, where they are exposed to all sorts of dangers. Unless 

 they were active creatures, they would soon succumb to their numerous 

 enemies. (Observe the development of the gnat in an aquarium.) 



Mouth Parts of 

 Female Gnat. 



(Enlarged fifteen 

 times. ) 



K., Pronotnm ; 01., 

 labrum ; Ok. , man- 

 dibles ; Uk., max- 

 illae; Kt., maxil- 

 lary palpi; Ul., 

 labium, with its 

 process (F.). 



