MUSCULATURE OF CATERPILLARS AND BEETLES 213 



They act variously as rotators, elevators, depressors, retractors, pro- 

 tractors, flexors, and extensors. 



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 synapter- 

 ous 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 know- 

 ledge 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 cater- 

 pillar. Newport's ac- 

 count 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 seg- 

 ments. In these segments 

 the first layer seen on 

 removing the fat and vis- 

 cera are the flat straight 

 recti muscles. They are 

 the most powerful of all 

 the trunk muscles, and are 

 those which are most con- 

 cerned in shortening the 

 body, in effecting the dupli- 

 cature of the external tegu- 

 ments 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. 



