ZOOLOGY FOR MEDICAL STUDENTS CHAP. 



nn a thread of silk, and in various species including the ordinary 

 silk-worm _ the larva of the Moth Bombyx mori the larva fashions this 

 thread into a cocoon with which it surrounds itself before entering on 

 the pupal 51 



Of the main orders of insects it is the DIPTERA that is of the greatest 



importance to the student of medicine. The most conspicuous charac- 



the reduction of the hind-wings to the club-like inconspicuous 



In the life-history metamorphosis takes place. The larva may 



the form of a -rub or maggot, living amongst decaying plant or 



animal matter, or leading a parasitic existence. In other cases the larva 



jtiatic, the details of the more or less elongated body differing in 



different cases (see e.g. Fig. 107). The many species of Mosquitos 1 or 



> are grouped together under the name Culicidae. They feed com- 



monly on plant juices but in the female, which alone sucks blood, a 



meal of Blood is apparently essential for the complete growth and 



maturation of the eggs. 



In marshy districts in the tropics, e.g. in tropical America, mosquitos 



may exist in such numbers as to make life almost intolerable to freshly 



arrived human beings, although fortunately immunity is eventually 



developed to the poison of their bite. The main objectionableness of 



mosquitos resides, however, not in the irritation caused by their bite 2 



hut in the fact that they are the transmitters of various disease-producing 



parasites. In this connexion there are two specially important types to 



In- distinguished, represented respectively by the genus Culex and the 



- Anopheles both of them common in warm and temperate climates. 



As the anopheline type is responsible for transmitting the parasite of 



malaria it is important to be able to distinguish it from the culicine type. 



correct identification of the species of mosquitos is a matter for 



specialists but there are certain conspicuous peculiarities which usually 



nable one to recognize an anopheline mosquito at a glance. The most 



conspicuous of these is the attitude assumed by the mosquito either 



M at rest or when about to bite. The culicine mosquito assumes the 



attitude shown in the right-hand figure at the top of Fig. 107 : the 



irly parallel to the substratum ; the head and proboscis is 



the ordinary Spanish word for a small fly, although in English 

 be used in n restrirfrd sense for the long-legged gnats called in 



do. 



t.ition caused l>v the. injection of the mosquito's salivary 

 ue not to ;my poison excreted by the mosquito, but to the 

 ,l>ioti< fun.ui t>rjoning to the group Eiitomophthorincae which 

 " k-(-like divertinda of the oesophagus and are passed into the 

 ith tin- Ball lion when the mosquito bites. 



