68 THE MICROSCOPE. 



The hemispherical head of the gnat, with its two large 

 compound eyes, will be seen at once to be furnished with 

 a long, cylindrical proboscis (<:), a pair of antennae (<?), 

 and a pair of labial palpi (b\ This cylindrical probos- 

 cis is the homologue of the labium, or lower lip ; it is 

 covered with lined scales for a considerable portion of 

 its length, and is expanded at the tip into three pairs 

 of concave leaves. On the upper side of this pro- 

 boscis is a groove, out of which spring six long, thin 

 filaments (d\ representing the mandibles, maxillae, 

 tongue, and labium. " The labium," writes Mr. Gosse, 

 " does not enter the wound. If you have ever had 

 the philosophic patience to watch a gnat while punc- 

 turing your hand, you have observed that the knob 

 at the end of the proboscis is applied to the skin, and 

 that then the organ lends with an angle more and 

 more acute, until at length it forms a double line, 

 being folded on itself, so that the base is brought into 

 close proximity to the skin. Meanwhile the lancets 

 have all been plunged in, and are now sunk into your 

 flesh to their very bottom, while the labium, which 

 formed merely the sheath for the whole, is bent up 

 upon itself, ready again to assume its straight form as 

 soon as the disengaged lancets require its protection."* 

 The proboscis, or hausiellum, of the Lepidoptera 

 (butterfly and moth tribe) will furnish you with a large 

 stock of interesting matter for study. The long spiral 

 organ must be familiar to the most castia', observer. 

 An examination of the structure of a butterfly's mouth 

 will show us that the most important organs are here 

 represented by the maxillae, which are immensely 

 elongated. The labrum and mandibles have their 

 homologues in three small triangular plates, not easy to 

 discover ; the labial' palpi appear one on each side of 

 the spiral coil. The maxillae are united, and form a 

 * " Evenings at the Microscope," page 183. 



