934 



JNSECTA. 



another of the Melolonthida, Rhizotrogus 

 castaneus,* three distinct legs originated by 

 separate trochanters from a single prothoracic 

 coxa of the right side (Jig. 399, A). But per- 



Fig. 399. 



A, Khissotrogus castaneus; B, Scarites Pyrachmon , 

 C, legs of ditto ; E, F,G, different views of a treble 

 tarsus of Carabus perforat us (Asmuss). 



haps the most remarkable example is that given 

 by Lefebvref of Scarites Pyrachmon (B), in 

 which from a single coxa on the left side of 

 the prosternum two trochanters originated 

 (fig. 399, B, C). The anterior one, the proper 

 trochanter, supported the true prothoracic leg ; 

 while the posterior one, in the form of an 

 oblong lanceolate body, attached to the base of 

 the first, supported two additional legs equally 

 well formed as the true one. Dr. Asmuss has 

 also givori an example in Carabus perforates 

 of a treble fifth joint in the tarsus of 'the left 

 meta- thoracic leg (E, F, G), in which all the 

 claws of three distinct tarsi exist. 



The principles upon which the modifications 

 of form, and the existence of supernumerary 

 parts depend, as attributable to retarded or ex- 

 cessive development, have been particularly 

 insisted upon by Saint Hilaire, Professor Grant, 

 and other comparative anatomists, in reference to 

 the development of the body in vertebrata, and 

 are equally applicable to that of the invertebrata. 

 That these aberrations of form really depend 



Bassi. 



tab 



Ma 8 asin d'Entomologie, fascicul. 5, 



upon an arrest of development is wefl show* 

 in the instance we formerly gave of Geotrupts 

 stercorarius (jig. 332), in confirmation of the 

 views of Savigny, respecting the different kinds 

 of appendages in each segment being simply mo- 

 difications of the same normal structure. That 

 retarded development is capable of producing 

 these aberrant forms we once satisfied ourself 

 by experiment made on a specimen of Sphinx 

 ligustri. We carefully watched a larva that 

 was about to undergo its change into the pupa 

 state, and when it was beginning to assume 

 that condition, retarded its development by 

 repeatedly touching and otherwise disturbing 

 it, the result of which was that the projecting 

 ease that usually exists on the point of the 

 perfect pupa of this insect was not developed 

 in the pupa in question, which we still possess, 

 and which exhibits an uniform appearance of 

 its exterior almost precisely similar to that of 

 Sphinx populi. With regard to the existence 

 of supernumerary limbs, it is presumed, in the 

 absence of any evidence that these additional 

 parts exist also in the larva, as we suspect they 

 do, as well as in the perfect insect, that they da 

 not originate simply by a greater development 

 of one part than of another during the changes 

 of the insect, but upon an original tendency to 

 the production of them which existed in the 

 germ itself. This opinion seems to be supported 

 by the circumstance, that although there is a 

 tendency to the reproduction of the same parts 

 as a normal condition of the wings in some 

 insects, such reproduction is not known to occur 

 as an abnormal condition, which appears to be 

 accounted for by the circumstance that the wings 

 themselves are simply developments of parts of 

 other structures, the respiratory organs. 



The muscular system of Insects, like that of 

 other Articulata, is contained within the dermo- 

 skeleton. It is composed of an immense 

 number of distinct, isolated, straight fibres, 

 which are not constantly aggregated together 

 in bundles, united by common tendons, or 

 covered by aponeuroses to form distinct mus- 

 cles, as in Vertebrata, but remain separate 

 from each other, and only in some instances 

 are united at one extremity by tendons. The 

 greater number of these fibres are flat, thin, 

 and of the same size throughout their whole 

 length, a few only being slightly conical. They 

 are arranged parallel to each other, and form 

 layers, or series of fibres. These series of 

 fibres, or layers, we prefer to regard as sepa- 

 rate muscles, rather than as aggregations of 

 muscles, as they were formerly regarded by 

 Lyonet,* because we are thereby enabled to 

 simplify our description of the muscular sys- 

 tem of these animals. But besides these layers 

 of fibres, which form the greater part of the 

 muscular system, there are also certain sets 

 of fibres which are united by tendons to con- 

 stitute distinct muscles, but they are not in- 

 closed by aponeuroses. The muscles of in- 

 sects differ, then, as remarked by Straus, f from 



* Traite Anatomique tie la Chenille qui ronge 

 le bois de Saule, 1760. 



t Considerations, &c. p. 145. 



