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not sought for particular differential characters between these two vari- 

 eties of the same species, their respective size sufficing for my present 

 object. Both varieties of the C. mosquito present the following distinctive 

 characters: the body is dark colored, sometimes almost black or steel- 

 colored ; the ventral segments of the abdomen as well as the dorsal ones 

 appear strengthened by an outer layer, with white rings corresponding 

 to the inter-spaces, though sometimes (on the ventral side) the segments 

 are whitish and the inter-spaces are dark. On each side of the abdomen 

 there are two rows of pearly-white dots, between which, after feeding, a 

 transparent, membrane stretches allowing the blood or other contents of 

 the distended stomach and intestine to be seen. Upon the hind legs 

 there are five very characteristic white rings, corresponding to the arti- 

 culations of the tarsus, metatarsus and tibia; the latter sometimes pre- 

 senting a sixth white spot. The middle and front legs present two or three 

 white rings. Upon the sides of the thorax are seen 8 or 10 white dots or 

 patches of irregular outline, and upon the antero-superior surface of the 

 thorax a combination of white lines on a dark background is seen resem- 

 bling a two-stringed lyre. The palps and the antennae also carry some 

 white marks. Some of the aforesaid markings are apt to be effaced with 

 age or by friction, but the most characteristic ones very seldom disappear. 

 The wings of the C. mosquito, the venation of which I small not describe 

 at present, have no spots like those of the European Culex annulatus; 

 and its wings are so short that, when closed, they leave the last segment 

 of the body uncovered. Or course, in order to observe the characters 

 which I have been describing it is necessary to use a magnifying glass ; 

 aplanatic lenses of 2i/> or 3 inches focus are very convenient for that 

 purpose. 



The males of both species are readily recognized by their feathery 

 antennae, like a pair of mustachios, and by its three-pronged proboscis 

 due to the long palps which lie close to the probocis above, but stand 

 out on each side near the point; thereby showing a marked contrast with 

 the smooth probocis of the female whose short palps barely cover the 

 upper sixth of its length. 



The two species of mosquitos to which I have referred do not come out 

 at the same hours: the zancudo comes out at night and the C. mosquito 

 in the daytime. This distribution of the day and night between the two 

 species made me think that the zancudo, notwithstanding its larger size 

 and more robust appearance, might not be constituted to stand the heat 

 of our summer sunshine. I tried, therefore, the following experiment. On 

 the 9th of June, at noon, I exposed to the direct rays of the sun the bulbs 

 of my psychrometer ; after half an hour the dry bulb marked 42°,25 C. 

 and the wet bulb 31° 75. I then substituted in place of the instrument 

 a tube in which a zancudo had been confined for 5 days, but continued 



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