March, 190r.] THE YICTORIAN NATURALIST. 217 



The head, concerned with sense organs, and food-gett- 

 ing, bore the usual compound eyes, the feelers or 

 -antennas, delicate sense organs about whose use we know 

 but little; and the wonderful beak or proboscis. The 

 latter really consists of a very perfect and complete set 

 of appliances for blood-sucking purposes. The upper lip 

 is much elongated, and is tubular in cross-section. The 

 first pair of jaws (mandibles) is much elongated, and very 

 sharp and delicate, to serve as lancets to pierce the flesh 

 of the unoffending victim. The second pair of jaws (first 

 maxillae) are also elongate, but are stouter than the man- 

 dibles. The lower ends of these are toothed, so that they 

 are modified into very delicate and effective saws. The 

 third pair of jaws (second maxillae) have grown together 

 and formed the large tubular structure known as the beak 

 or proboscis. Thus, this is really a case to enclose and 

 support the very delicate surgical instruments within. In 

 addition to these five elongate piercers (upper lip, two 

 lancets, and two saws), the mosquito has the honour of a 

 new structure. Nature modifies an existing structure to 

 any required extent, but she seems very reluctant to allow 

 a new structure, so that the mosquito is highly honoured. 



The extra structure serves two purposes. First, it con- 

 veys the saliva down into the blood of the victim, for this 

 saliva, being used to thin down the blood and prevent its 

 coagulation, would be useless in the mosquito's mouth. It 

 is wanted down in the victim's blood, so the salivary duct 

 is continued down a fine structure called the " hypo- 

 pharynx." This structure, being flattened, serves also to 

 close the tubular upper lip, so that the blood can be 

 drawn up that into the mosquito's body 



When a mosquito bites, it places the end of the lower 

 lip on the victim's hand, and shakes its head, thus sawing 

 through the skin. The lower lip now bends up near the 

 head, and so the end of it is raised, while the six piercers 

 sink into the flesh. The muscular throat now acts as a 

 pump, and the blood is speedily pumped up. 



In return for our kindness in giving the mosquito blood, 

 she gives us with the saliva two things we decidedly 

 object to. First there is poison, which produces a most 

 irritating effect on some people, while others seem to be 

 immune to it. Secondly, there are very tiny microscopic 

 animals, which give rise to the deadly diseases already 

 mentioned. The mosquito is the involuntary, but neces- 

 sary, agent in the transmission of these animals ; but why 

 2761. c 



