Our knowledge of the muscular system of insects is still very imperfect. To work it out thoroughly one should begin first with that of Scolopendrella, then some generalized synapterous form, as Japyx or Lepisma, then passing to that of a caterpillar, and ending with some of the more highly specialized forms, such as a beetle, etc. Thus far our knowledge is confined to that of the caterpillars (Lyonet, Newport, and Lubbock) and the beetle (Straus-Durckheim) and ants (Forel, Lubbock, and Janet). =Musculature of a caterpillar.=—Newport’s account of that of the larva of _Sphinx ligustri_ is the most useful (Fig. 231). The muscles here present, he says, great uniformity of size and distribution in every segment, the motions of each of these divisions of the body being almost precisely similar, especially in the 4th to 9th trunk segments. In these segments the first layer seen on removing the fat and viscera are the flat straight recti muscles. They are the most powerful of all the trunk muscles, and are those which are most concerned in shortening the body, in effecting the duplicature of the external teguments during the changes of the insect, and which during the larval state mainly assist in locomotion. There are four sets, two dorsal and two ventral (Fig. 231, _A_, _A_). Without entering into farther details, the reader is referred to the works of Newport and to Fig. 231. =Musculature of a beetle.=—The best general account of the musculature of a perfect insect is that of Straus-Durckheim in his famous work on the Melolontha. We will copy the summary of Newport, who adopted the nomenclature applied to these parts by Burmeister:—