54 SUPPLEMENT ON 



much to the movement. The rings of the abdomen are, in 

 general, articulated on each other in the same manner, so 

 that the muscles on one segment, are pretty nearly the same 

 on the preceding, and on the following. 



As most of the articulations are performed in ginglyraus, 

 two muscles are sufficient to produce them — an extensor, in 

 general the smaller, and a jflector or abductor, much more 

 voluminous. These muscles are always placed in the cavity 

 of the articulations, so that all the corneous pieces of the limbs, 

 for example, are cases for the muscles. 



There is this difficulty in the study of the muscles of 

 insects, that they are truly circumscribed, and distinct only 

 at their insertion, or the termination of their fibres on a solid 

 tendon, or articulated prolongation of the piece which they 

 are intended to move. As the insects are destitute of vessels 

 and cellular tissue, these fibres are not united together, and 

 when separated from their insertion, or fixed point of attach- 

 ment, they remain floating like tufts, which renders their 

 study very difficult. In the soft insects, as the grasshoppers, 

 in the orthoptera, in the diptera, but especially in larvae, and 

 caterpillars, this study is much more easy. Lyonnet, in his 

 excellent treatise on the anatomy of the caterpillar of the 

 cossus, has given capital figures of these organs of motion. 

 Swammerdam has also furnished us with very exact descrip- 

 tions and drawings of the muscles. More ample details on 

 this subject than we can afford to give, will be found in the 

 admirable work of Messrs. Kirby and Spence. The Barony's 

 " Comparative Anatomy" may also be consulted with advan- 

 tage, though the magnifiers used at the time of its publica- 

 tion (1805) were insufficient to detect the ultimate fibre, an 

 achievement since performed by M. Bauer, with improved 

 glasses. 



Insects are evidently endowed with a nervous system, and 

 this system is absolutely the same as that of the Crustacea 



