72 THE COCKROACH : 



The muscular fibres of Insects present some important 

 differences from the fibres just described. The nuclei are often 

 found in the centre, and not on the surface of the fibres in both 

 Insects and Crustacea. In both classes the fibrils are frequently 

 subdivided into longitudinal strands, which have not been 

 distinguished in Vertebrate muscles (Viallanes). The sarco- 

 lemma is often undeveloped. Lastly, Insects, like other 

 Arthropoda, exhibit the remarkable peculiarity that not only 

 their voluntary muscles, but all, or nearly all, the muscles of 

 the body, even those of the digestive tube, are striated.* 



t 



General Arrangement of Insect Muscles. 



The arrangement of the muscles in an Insect varies greatly 

 according to situation and mode of action. Some of the 

 abdominal muscles consist solely of straight parallel bundles, 

 while the muscles of the limbs usually converge to tendinous 

 insertions. In certain larvae, where the segments show hardly 

 any differentiation, the muscles form a sheet which covers the 

 whole body, and is regularly segmented in correspondence with 

 the exo-skeleton. As the movements of the body and limbs 

 become more varied and more energetic, the muscles become 

 grouped in a more complicated fashion, and the legs and wings 

 of a flying Insect may be set in motion by a muscular apparatus 

 almost as elaborate as that of a bird. 



Muscles of the Cockroach. 



The following: short notes on the muscles of the Cockroach, 



~ ' 



aided by reference to the figures, will render the more note- 

 worthy features intelligible. A very lengthy description, far 

 beyond our space or the reader's patience, would be required to 

 explain in detail the musculature of the head, limbs, and other 

 specialised regions. 



STERNAL MUSCLES OF ABDOMEN. The longitudinal sternal 

 musc/es (fig. 34) form a nearly continuous transversely seg- 



* The exceptions relate chiefly to the alary muscles of the pericardial septum. 

 Lowne (Blow-fly, p. 5, and pi. v. ) states that some of the thoracic muscles of that 

 Insect are not striated. 



