HARDWICKE'S SCIENCE-GO SSIP. 



109 



" Ceylon," notices this of the mosquito most pre- 

 valent in India (Culex laniger). " When you are 

 reading," he says, " a mosquito will rarely settle on 

 that portion of the hand which is within range of 

 your eyes, but, cunningly stealing by the underside 

 of the book, fastens on the wrist or little finger, and 

 noiselessly inserts his proboscis there." This is 

 just the method of the English Gnat, as many no 

 doubt can testify, who, indulge in reading out of 

 doors in the vicinity of lakes or ponds. In de- 

 scribing, then, the proboscis of the common Gnat, 

 that of many so-called mosquitoes may no doubt be 

 included, which gives the subject a wider interest. 

 The proboscis of the Gnat removed from its 

 sheath (of which we shall write afterwards) has 

 sis parts : the lip, or channel for the blood ; the 



tongue; the bands (two in 

 number) ; and two serrated 

 lancets. Let us describe 

 each of these in succession. 

 The lip (marked 1 in the 

 illustration), though finer 

 than the smallest needle, is 

 the largest and chief part 

 of the proboscis. It has an 

 average diameter of the one 

 thousandth part of an inch. 

 It is an open, boat-shaped 

 channel, through which the 

 blood of ihe victim is drawn ; 

 the end is pointed, and at 

 this part is narrowed just 

 sufficiently to hold firmly the 

 end of the tongue which 

 passes through it. After 

 entering the head, the lip 

 takes a tubular form, and 

 terminates in a globular 

 enlargement, which is con- 

 nected with the pumping 

 instrument in the thorax 

 and the viscera. 



The tongue (2) is a long, 

 very slender tube, supported 

 along its whole length by a 

 membrane of the same width and length as the lip, 

 which it exactly covers, so as to make it, with the 

 aid of the bands, an air-tight channel. The bands (4), 

 one onfeach side, are exceediugly slender bodies, 

 being strips of delicate membrane, broad at the base 

 near the head and tapering gradually towards their 

 extremities; they are there thickened; at the edge> 

 and become again a little broader. The use of these 

 is to enwrap the edges of the tongue-membrane so 

 far as they extend, which is nearly to the end ; the 

 thickened edges in this part fitting by a notch over 

 the rim of the lip, and, at the same place, passing 

 across the tongue from side to side, keep it in place. 

 The thickened ends (seen at No. 4) also seem to 



Fig. 65. —~- 



Proboscis of Gnat, x 400. 



1. Lip or channel. 



2. Tongue (the tube), 



3. Lancets. 



4. 4. Bands (the ends). 



furnish a stay or rest for the shafts of the lancets, 

 against which they may slide correctly. The lancets 

 (3) are two, one on each side of the lip ; their shafts, 

 near the head of the insect, have broad membranes 

 for steadiness, and are, throughout their length, 

 thickened at the back. They move backwards and 

 forwards with an alternate motion. 



A wound being made with these, the lip is 

 gradually inserted, and the blood drawn into the 

 channel ; not, however, through its end, for that is 

 closed by the tongue, hut probably beneath the 

 edges of the tongue-membrane below its junction 

 with the bands. 



The use of the tongue- tube is not so obvious. 

 If traced upwards, it is found to enter the head, 

 passing through the upper part of the lip, and 

 terminates at the back of the insect's head in a large 

 pear-shaped gland. This is probably the poison- 

 gland ; and it seems to be the office of the tongue- 

 tube to convey the poison into the wound to liquefy 

 the blood, the globules of which, in the larger 

 animals, might otherwise be too large to find an 

 entrance ; or if otherwise, this addition to the food 

 may for some other reason be necessary. The tube 

 of the tongue, being in advance of the lip, brings 

 the poison well in contact with the blood. 



This delicate proboscis cannot be seen in the 

 living insect as it is represented in the illustration, 

 because it is covered throughout its entire length 

 by a strong, thick, elastic case or cover, split into 

 two parts, and thickly clothed with hair and 

 feathers. The Gnat, not having the power of ex- 

 tending the proboscis beyond this cover, or of re- 

 tracting it, a question arises as to how the proboscis 

 is brought into use. Reaumur, who, for the sake 

 of observation, courted the attention of these 

 insects, avers that the case is bent like a bow, until 

 the two ends meet. It is not easy to understand 

 how this could be, and we incline to think that this 

 illustrious observer, not being allowed by the wary 

 insects to look very closely, was under an illusion. 

 The proboscis is nearly half as long as the insect, 

 and it is, not easy to believe that so slender and 

 delicate an instrument could be driven to such 

 a depth and with such force as this supposition 

 implies. The Gnat has very long legs, and small 

 muscular power, and requires a long trunk to reach 

 its food. The case is, however, provided with a 

 hinge at a distance from the end, of about one-eighth 

 part of its length ; here it doubles back easily on 

 each side, and this part is lined with several very fine 

 leaflets, the whole formingakind of tassel, which hangs 

 loosely over the extremity of the proboscis (as much 

 of it as appears in the illustration). We are disposed 

 to contend that no more than this is brought into 

 use, and that it is quite sufficient to penetrate those 

 smooth and delicate parts of the skin which the 

 Gnat instinctively selects, on the wrist, the 

 temples, the knees, the ears, the eyelids, &c. How, 



