906 



INSECTA. 



a similar structure of the proboscis in Eristalis. 

 The submentum is the part in which the flexion 

 of the organ takes place ; the mentum, as in 

 the preceding instances, is a strong horny plate, 

 almost closed on its upper as well as its under 

 surface, and the ligula is horny, but terminated 

 by soft dilatable lips. The ligula is always 

 articulated by a distinct joint with the mentum, 

 and appears to be constantly present in this 

 order. In Asilus, as we have just remarked, 

 it is strong and corneous, but in the less rapa- 

 cious insects, as in Eristalis, and the Muscidte, 

 it is terminated by two dilated fleshy lips, 

 which we regard as the analogues of the 

 paragloss<e (Jig. 379, * i.) In Tabanus these are 

 exceedingly large and broad, and are widely 

 expanded to encompass the wound made by 

 the insect with its lancet-like mandibles in the 

 skin of the animal it attacks. The structure 

 of these paraglossae is curious. On their outer 

 surface they are fleshy and muscular, to fit 

 them to be employed as prehensile organs, 

 while on their inner they are more soft and 

 delicate, but thickly covered with rows of very 

 minute stiff hairs (*** i) directed a little back- 

 wards, and arranged closely together like the 

 teeth of a comb. There are very many rows 

 of these hairs on each of the paraglossae, and 

 from their being all arranged in a similar di- 

 rection are easily employed by the insect in 

 scraping or tearing delicate surfaces. It is by 

 means of this curious structure that the busy 

 house-fly often occasions much mischief to the 

 covers of our books by scraping off the albu- 

 minous polish, and leaving traces of its depre- 

 dations in the soiled and spotted appearance 

 which it occasions on them. It is by means of 

 these also that it teases us in the heat of summer 

 when it alights on the hand or face to sip the 

 perspiration as it exudes from and is condensed 

 upon the skin. The manner in which the 

 fluid ascends the proboscis is similar to that of 

 its ascent in other Haustellata, it being de- 

 pendent partly upon the sucking action exerted 

 by the application of the proboscis, assisted by 

 the muscular action of the paraglossae, as any one 

 may readily convince himself on watching the 

 motion of the parts in the common house-fly, 

 when sipping a drop of fluid, or moistening 

 the stolen grain of chrystallized sugar between 

 its paraglossae. 



The palpi yet remain to be noticed. Those 

 of the maxillae appear to be constant throughout 

 the whole order. In Culex they are very con- 

 spicuous parts, covered with hairs and as long 

 as the proboscis ; they are formed of three short 

 basial joints and three very long ones, the fourth 

 joint being more than twice the length of either 

 of the others. In Tipula and Empis they are 

 also six-jointed, but of moderate length. In 

 Tabanus also they are very conspicuous, and 

 appear to be formed of two short and one very 

 long joint densely covered with hairs, and serve 

 as a cover to the base of the proboscis. In 

 Asilus they are short, three-jointed, and slightly 

 hairy (Jig. 380, h), and they are equally con- 

 spicuous in most of the Muscida and Syrphida, 

 in which they are formed in general of two short 



joints and one very long one. In the common 

 Musca they are long and club-shaped, but in 

 Eristalis (fig. 379, g, h) and Volucella they are 

 long, slender, and sometimes covered with hairs. 

 The labial palpi do not appear to exist in 

 Diptera. Savigny believed that he had ob- 

 served at the base of the ligula in Tabanus a 

 pilose excrescence which he considered the 

 analogue of the labial palpi ; but although, as 

 Mr. Newman has remarked, the spot which 

 Savigny pointed out is exactly that at which 

 they ought to be situated if they really did 

 exist, we have been unable to detect them or 

 to confirm his opinion. 



In Homaloptera the head resembles that of 

 Diptera. It is rounded but flattened on its 

 upper surface, and is so closely approximated 

 to the anterior margin of the prothorax into a 

 notch in which it is inserted, as to appear as if 

 separated from it only by a suture. All the 

 primary parts found in the head in other insects 

 appear to be developed in some species of this 

 order. Thus the epicranium in Oxypterum is 

 broad, distinct, and channelled along the 

 median line into a deep groove (fig. 381, b), 



Fig. 381. 



The upper and under surface of the head in 

 Oxypterum. 



b, epicranium ; c, cornea ; d, clypeus posterior ; 

 d* , clypeus anterior ; e, labrum ; /, undeveloped 

 mandibles; g, maxilla j t, labiuin ; *, lingua. 



