INSECTA. 



905 



strong, with sharp cutting edges. They are short- 

 er and narrower than the mandibles, and are 

 usually inclosed within the sheath or proboscis 

 formed by the labium. In this family some of 

 their primary parts are easily distinguished. 

 Thus the blades (5) that lie within the sheath 

 of the labium, are the true laciniae in other 

 insects. These are articulated at their base 

 with the palpifer (3), a small triangular plate, 

 which bears the maxillary palpus and is situ- 

 ated most externally, and also with a broad 

 squamous plate (2), which is united at its base 

 to its fellow of the opposite side, and appears 

 to be analogous to the stipes and cardo(l) 

 united. This plate, with its fellow, forms the 

 anterior boundary of the throat, and is closely 

 united to the proper gula that bounds the 

 anterior margin of the occipital foramen. The 

 muscles attached to the posterior margin of the 

 mentum and submentum pass over this plate 

 to be attached, one set to the anterior margin of 

 the gula, and the other to the posterior. In 

 Volucella bombylans the maxillae have lost 

 much of their importance, but are still easily 

 distinguished, and, with the other parts of the 

 mouth, are beginning to be merged in the 

 united fleshy proboscis. The cardines, upon 

 which all the motions of flexion and extension 

 in this kind of mouth depend, are very largely 

 developed. They are two elongated plates, 

 approximated to each other along their inner 

 margins, and to two triangular plates, the re- 

 mains of the mandibles, at their anterior and 

 lateral. The cardines thus form the posterior, 

 or basilar part of the proboscis, and the plates 

 which, from being articulated within the 

 margin of the clypeus posterior, we regard as 

 analogous to the mandibles, the lateral. At 

 their inferior portion, which forms the joint or 

 elbow of the proboscis, the cardines are freely 

 articulated with the stipes, which is a short 

 plate not easily distinguished from a part of the 

 mandible with which it is also in apposition. 

 Between the stipes and cardo is a short trian- 

 gular plate, the palpiger, rounded at its most 

 inferior part, and, with its fellow of the oppo- 

 site side, assisting to form the elbow or joint of 

 the proboscis. The maxillary palpus, which 

 aises from its external border, is long and 

 slender, and appears to be formed of three 

 short joints and one very long one. At the 

 inner and anterior margin of the palpifer and 

 stipes is articulated the lacinia, which, as in 

 Asilus, is of considerable length. It is inte- 

 resting to remark, that in this insect, which is 

 parasitic in its habits, insinuating itself into 

 the nests of humble-bees to deposit its eggs, 

 the mandibles, as just shewn, are atrophied, and 

 the two laciniae of the maxillae, although dis- 

 tinct from each other, are approximated in the 

 middle line to form the anterior or upper sur- 

 face of the tube to the mouth, as in Hymen- 

 optera, the sides and lower portion of the tube 

 being formed by the labium, and all the motions 

 of extension and flexion in the proboscis being 

 dependent upon the cardines, as we have before 

 seen in Hymenoptera. In this genus there- 

 fore we discover one of the transitionary forms 



of mouth from that of the blood-sucking in- 

 sects to those of the more omnivorous feeders, 

 all the parts of the mouth being less and less 

 distinct in proportion as the act of taking food 

 is less complicated. Thus we have seen that 

 in Tabanus distinct mandibles are required to 

 pierce the skin of an animal, before the food is 

 accessible; but in the Muscida, whose fluid 

 aliment is every where present, a complicated 

 form of mouth is unnecessary, and accordingly 

 we find it reduced to a simple sucking tube. 

 In Eristalis the maxilla are present, as in 

 Asilus and Volucella, as also are their palpi, 

 which are nearly equal to them in length. In 

 Eckmomyia they are less distinct than inVolu- 

 cella. The anterior part of the proboscis at its 

 base is formed simply by a broad membrane 

 united to the anterior margin of the atrophied 

 mandibles, while the laciniae, which were dis- 

 tinct in the preceding genera, are united in 

 this genus to form the front of a lower portion 

 of the organ. That this union has taken 

 place is shewn in the presence of the maxillary 

 plpi, which invariably exist in Dipterous 

 insects. In all the Muscida the palpi arise 

 from a distinct palpifer, which appears to be 

 connected with a proper stipes, but the re- 

 maining parts are not easily distinguished. 

 It seems evident, however, that at least the 

 basilar portion of the proboscis is formed by 

 the union of the laciniae above and the labium 

 below, as in Hymenoptera, and that the la- 

 bium forms the chief portion of the organ, 

 contrary to the opinion of Desvoidsy, who 

 believed that the proboscis of Diptera was 

 formed of the maxillae alone, and to that of 

 Savigny, who regarded the proboscis as formed 

 only of the labium. The principle therefore 

 upon which the proboscis of Diptera is con- 

 structed, is precisely analogous to that of 

 Hymeuoptera, but there are important diffe- 

 rences in the form of similar parts in the two 

 orders. The labium includes the same primary 

 parts as in Hymenoptera, but the labial palpi 

 are almost invariably absent. The submentum 

 is usually indistinct. In Asilus the part we 

 regard as such is a small triangular plate, (m,) 

 distinguished only when the parts are examined 

 by transmitted light. It is situated between 

 the anterior portions of the two cardines. In 

 Volucella it is that part of the proboscis which 

 is nearest to the cardines, close to the articu- 

 lation. In Culex, in which the cardines are 

 short, it is situated very close to the under 

 surface of the head ; in other Diptera it is fre- 

 quently very indistinct. The mentum on the 

 contrary is always a conspicuous part. In 

 Asilus it is the broadest part of the proboscis (/). 

 It is a strong horny plate, deeply channelled on 

 its upper surface to form a canal to the mouth, 

 and receive within it the mandibles and max- 

 illae. It is articulated with the ligula, or ex- 

 tremity of the proboscis (*), which is distinctly 

 formed of two halves approximated together, 

 and naiTowest at the apex, with three slight 

 lateral dilatations. In Volucella the mentum 

 in like manner is a strong deeply channelled 

 plate, covered above by the laciniae. There is 



