THE CRANE-FLY 129 



termittent fevers was established, and it was discovered that 

 each recurring attack of the fever corresponds to the libera- 

 tion of a fresh crop of spores or malaria-germs. Quinine 

 destroys the parasite without injuring the patient, and is 

 therefore a powerful remedy against malaria. The next step 

 in the inquiry was to discover how the malarial parasites 

 entered the blood. Dr Manson suggested, and Major Ross 

 in 1897 proved, that mosquitoes (which are only gnats under 

 another name) are the agents. The gnat draws blood, and 

 in the very act infects the patient with the malaria-germ. 

 An uninfected gnat becomes infected by drawing blood which 

 contains malaria-germs. They multiply in the body of the 

 insect, and, after completing their own life - cycle, produce 

 and set free vast numbers of rod-like bodies, which accumu- 

 late in the poison-glands and their ducts, to be introduced 

 at the first opportunity into another human victim. Now that 

 the cause of malarial fevers is ascertained to be intimately 

 connected with the bites of particular gnats, the search for 

 means of prevention becomes hopeful, and it may not be 

 very long before the malarial districts of the tropics are 

 rendered perfectly safe to Europeans. 



26. THE CRANE-FLY {Tipuh oleracea and allied species) 



This very common insect is known as a larva by the name 

 of leather-jacket, and in the winged state as the crane-fly, 

 or daddy-longlegs. The larva is subterranean, and is hardly 

 ever seen except when a sod is lifted. The toughness of its 

 skin suggested the popular name of leather-jacket. It attains 

 a length of nearly an inch and a half, is of a dull brown or 

 dark grey colour, and is not unlike a fragment of a small twig. 

 On examining it closely, the head can be distinguished. It 

 is rather small, hard, and retracted within the prothorax for 

 two-thirds or more of its length. As is usual with retractile 

 heads, the chitinous wall is imperfect, and shows large gaps 

 or incisions. There are no limbs ; the feelers are rather 

 short and three-jointed; the mandibles strong and toothed, 

 the maxillffi reduced to mere vestiges. The labium is repre- 

 sented by two plates, one in front of the other, with their 

 fore-edges toothed. Against these teeth the mandibles play 



