THE MUSCULAR SYSTEM. 31 



In describing Insects the vertex^ or crown, of the head is the 

 highest part ; and the front is the part usually in front of the 

 insertion of the antennae. 



The Muscular System lies just beneath, and is continuous 

 with the integument. It consists of numerous "distinct isola- 

 ted straight fibres, which are not gathered into bundles united 

 by common tendons, or covered by aponeuroses [or tendinous 

 sheaths] to form distinct muscles, as in the Vertebrata, but 

 remain separate from each other, and only in some instances 

 are united at one extremity by tendons." (Newport.) These 

 minute fibres form layers, which Newport regards as separate 

 muscles. "Each fibre is composed of a great number of very 

 minute fibrillae, or fasciculi of fibrillar," and has been observed 

 by Wagner and Newport to be often striated as in Vertebrates. 

 The muscular system is simplest in the lower insects and the 

 larvae of the higher forms, and is more complex in the head 

 than elsewhere, and more complex in the thorax than in the 

 abdomen. These minute muscles are exceedingly numerous. 

 "Lyonnet, in his immortal work on the anatomy of the lan-a 

 of Cossus lignijyerda, found two hundred and twenty-eight dis- 

 tinct muscles in the head alone, and, by enumerating the fibres 

 in the layers of the ditferent segments, reckoned 1,647 for the 

 body, and 2,118 for the internal organs, thus making together 

 3,993 muscles in a single larva. In the larva of Sphinx ligus- 

 tri we have found the muscles equally numerous with those 

 discovered by Lyonnet in the Cossus." (Newport.) 



The muscular system corresponds to the jointed structure of 

 insects, as do the other internal systems of organs. Of the 

 muscles belonging to a single ring, some stretch from the front 

 edge of one segment to the front edge of the next, and others 



of the Scorpion, whose mode of development appears to be precisely similar to 

 that of a telson. In the same category we must rank the labrum in front of the 

 mouth, which in the Crustacea (at least) appears to be developed from the sternum 

 of the antennary, or third somite, the metastoma (or so called labium, or lingua) 

 of Crustacea, and the lingua of Insecta, l)ehind the oral aperture. 



" However much these appendages may occasionally simulate, or play the part 

 of appendages, it is important to remember, that, morphologically, they are of a 

 very different nature, and that the confusing them with true api)endages must 

 tend completely to obscure the beautiful relations which obtain among the dif- 

 ferent classes of the Articulaia." — Huxley, Linn%an Transactions, vol. xxii. 

 London. 



