INSECTA. 



933 



tarsi, as in the latter instances.* Those insects 

 which support themselves upon the surface of 

 water, as the common gnat, have the under 

 surface of each tarsus covered with rows of 

 fine hairs, which repel the water, and support 

 the insect upon the surface. If the under sur- 

 face of the tarsi be wetted with spirits of wine, 

 the insect can no longer support itself upon 

 the surface, but immediately sinks down.f 

 When the legs are employed in jumping, as in 

 Hulticti, the destructive flea-beetle of the 

 turnip, and the Gryllida and Locustidtf, the 

 posterior pair, upon which devolves the greatest 

 effort, as in the swimming insects, are con- 

 siderably larger than the others ; the thighs in 

 particular are enlarged and lengthened, to 

 allow room for the insertion of the muscles. 

 But when the legs are employed in digging or 

 burrowing, it is the anterior pair that become 

 the most important, as in the mole-cricket, 

 Gryllotalpa(G). In that insect the coxa (a) 

 is of an enormous size, and the trochariter at- 

 tached to its inferior margin consists of two 

 distinct articulations, one of which projects in 

 a lobulated form, and probably is useful in 

 assisting to remove the earth during the ope- 

 rations of the insect. The femur (6) is short 

 and broad, and is articulated both to the coxa 

 and trochanter, and thus derives additional 

 strength from its more secure connexion with 

 the base of the limb ; while the tibia (c), which 

 is the part immediately employed in burrow- 

 ing, is also short, and divided at its extremity 

 into four strong curved spines, directed out- 

 wards, and forming as it were a broad hand, 

 like the claw of the mole, for digging into and 

 rapidly removing the earth in its burrow. The 

 tarsus (d), which appears to be almost useless 

 in these subterranean labours, consists of three 

 short articulations, which are attached to the 

 external surface of the tibia. A similar con- 

 formation of the tibia exists in other burrowing 

 insects, since it is always this part of the 

 limb that is employed in digging, and not the 

 tarsus, which is used only in scraping or 

 scratching away loose soil, as by the oil-beetles, 

 Me lot, and the sand-wasps. Thus in the 

 Scarab&ida and Geotrupida the anterior 

 tarsi are broad and dentated laterally, and the 

 posterior ones are armed with strong spines. 

 In some genera, as in the Coprides and 

 Onthophagi, the extremities are not only 

 strongly spined, but are also broad and club- 

 shaped, to assist them in penetrating into the 

 loose excrement beneath which they are ac- 

 customed to burrow. 



There are circumstances connected with the 

 organs of locomotion in insects of considerable 

 interest, and which cannot be passed over. 

 These are the aberrations of form which they 

 undergo as a consequence of incomplete de- 

 velopment, and the occasional existence of 

 supernumerary limbs, the result of an opposite 

 tendency in the development of the germ. 

 We have already alluded to the changes of 

 form occasioned by the former of these circum- 



* Degeer Memoires, t. ii. p. 810, pi. 28. 

 t Dr. Roget's Bridgewater Treatise, vol. i. 



p. 334. 



stances, and we have now to notice the not less 

 remarkable occurrence of the latter. Although 

 every part of the body is subject more or less 

 to these occurrences, the supernumerary parts 

 are almost always antennae or legs. We do 

 not remember a single instance of a supernu- 

 merary wing, or elytron, or organ of mandu- 

 cation, although the whole of these parts are 

 occasionally subjected to an aberration of form 

 in consequence of imperfect development. 

 Many instances of this kind are given by Dr. 

 Herrmann Asmuss,* who has collected a mul- 

 titude of facts connected with this interesting 

 subject, from which it appears that abnormal 

 forms are more frequent in the antennae and 

 legs than in other parts of the body. Only 

 one instance is given of abnormal form of the 

 mandible from arrested development, but 

 several of the antennae and legs. But the 

 most frequent abnormal condition is found in 

 the existence of supernumerary parts. Of 

 these he has given two instances in which the 

 antenna on one side of the head was double. 

 These occurred in one of the Elateridte, Athous 

 hirtusj\ and Carabus auratus,\ and one instance 

 also in which it was trifurcated, in Helops 

 carulens. But it is remarkable that the most 

 frequent occurrence of supernumerary parts is 

 of the legs. Of these Asmuss has collected 

 eight examples, and it is remarkable that in 

 six of them the parts on one side are treble. 

 Of the two instances in which the parts were 

 double the first occurred in Agriotes obscurus,\\ 

 in which there were two perfect prothoracic 

 legs on the right side of the body, connected 

 with the sternum by two distinct coxa?. In 

 the other instance, which occurred in Tele- 

 phorus Jmcus^ there were two meso-thoracic 

 legs on the left side, connected together, and 

 attached by a single coxa to the sternum. 

 To these we may add a third instance, which 

 occurred in Chrysomela hcemoptera, captured 

 by Mr. Curtis, and described in his British 

 Entomology.** In this specimen the super- 

 numerary part is a tibia, apparently moveable, 

 and developed from the extremity of the femur 

 of one of the hinder pair of legs. A similar 

 remarkable condition is described by Tiede- 

 mannff as having occurred in Melolontha vul- 

 guris, in which three tibiae and tarsi originated 

 from a single coxa of the right metathoracic 

 leg. Asmuss alludes also to the specimen of 

 Oryctes nasicornit described by Audouin,^ in 

 which a similar number originated from the 

 right prothoracic leg; and to a second example 

 of Melolontha vulgaris in which three tibiae 

 and tarsi originated from a triangular, spatula- 

 formed femur of the right prothoracic leg. In 



* Monstrositates Coleopterorum, Rigae et Dorpati, 



t Bassi. 

 J Douraerc. 

 $ Seringe. 

 || German 

 f Bassi. 



** PI. 111. Apr. 1826. 



tt Meckel's Archiv itir Physiologic, t. v. 1819. 

 p. 125. tab. 2, fig. 1. 



Jf Annales de la Soc. Entom. de France, 1834. 

 H Doumerc. 



