217 



Britaiinica " would interest you most. This author says : " No 

 " notice of the nioscjuito or gnat would be complete without an 

 " explanation of the mouth j^arts by which it is enabled to cause 

 " such extreme irritation. When these parts are closed one upon 

 " the other the whole looks like a long proboscis, but in reality 

 *' this consists of seven distinct slender pieces separated to the 

 " base, viz : the labium, two maxilhf, two mandibles, the Hn(/ua, 

 " and the la'^rutn. The nomenclature of the mouth-parts 

 " A aries with different authors. G. Dimmock (Anatomy of the 

 " J/oufh-parts and of the Sucking-apparatus of some Diptera), the 

 " latest investigator of this complex apparatus, states, that the 

 " labium has for function for the most part, the 2:)rotection of the 

 " fine sefie which form the true piercing organ of the Culex. In 

 " the female of Culex the protective sheath is formed by the 

 " labium alone. When the mosquito has found a place which 

 " suits it for piercing^for it often tries different places on our 

 " skin before deciding on one — it plants its labellm firmly upon 

 " the spot and a moment later the labium is seen to be flexing 

 " backwards in its middle ; the setce, firmly groujDed together, 

 " remain straight and enter the skin. When the setee haA^e 

 " entered to nearly their full length, its labium is bent double 



" beneath the body of the insect 



" The withdrawal of blood is effected by means of a pumping 

 " apparatus at the base of the mouth-parts. As no investigator 

 " appears to have been able to detect a poison gland, it has been 

 " considered that the irritation caused by the bite of a mosquito 

 " was solely of mechanical origin ; but the extreme irritation and 

 " its duration have not caused this idea to be commonly accepted. 

 " Dimmock avows his belief that there is use made of a jDoisonous 

 " saliva. In the male of Culex the mouth-parts vary considei'ably 

 " from those of the female — a conspicuous point of difference being 

 " that in this sex the mandibles are absent, and the maxillae are 

 " not barbed." 



" About 35 species of Culex (mosquito or gnat) have been 

 " described as inhabiting Europe, and about 130 from the rest of 

 " the world, but their difterentiation is involved in great difficulty 

 " and uncertainty, and it is probable that the number of true 

 " species may be very much less." 



So far as Trinidad is concerned I may say I have observed at least 

 tendifterent kinds of mosquitoes, varying in colour and size, and the 

 bite of some of them is far from being pleasant. In most natural 

 history books you will find something about swarms of gnats 

 which turned up in different places and at difierent times. The 

 principal abode of mosquitoes is on the banks of rivers, but as you 

 all know at this moment we have a good many about our houses. 

 On the Orinoco, saj^s Humboldt, the first question in the morning 



