THE ORGANS OF SKNSATION. 2G9 



inferior margin of the occipital aperture. The third is formed by 

 small muscular strips, which originate from the pectoral plate of the 

 first segment of the body, and affix themselves beneath the former at 

 the large occipital aperture. 



The rotators are divided on each side into two fasciculi, the superior 

 one of which springs more from the dorsal side, and the inferior one 

 from the pectoral side of the first segment of the body, and insert 

 themselves in the skull, closely contiguous to the margin of the occi- 

 pital aperture. The inferior ones are in general the shortest bundles, 

 and the superior ones the weakest. They both appear to me to be 

 merely modifications of the oblique lateral muscles, as those profounder 

 extensors and flexors may possibly be merely transformations of the 

 oblique dorsal and pectoral muscles. 



The muscles lying in the head itself, which move the oral organs 

 and the antennae, agree so much in form, situation, and insertion with 

 those above described belonging to the perfect insect, that their small 

 divarications, which proceed from the less developed state of the ske- 

 leton of the head, require no further notice, particularly as they stand 

 in precise connexion with the various forms of the head, and their 

 special description consequently exceeds the boundaries of our object. 

 We must here, however, notice of the apparently headless larvae of the 

 Diptera, that the most anterior membranous segment of the body 

 takes the place of the head, and that its anterior orifice is the mouth, 

 which is armed with several, generally four, frequently bent setae, which 

 receive their peculiar extending and withdrawing muscles. They lie 

 withdrawn in the bag-shaped oral cavity, and appear, from their 

 darker colour, through the pointed anterior end of the larva as a black 

 body. 



FOURTH CHAPTER. 



OF THE ORGANS OF SENSATION. 



182. 



THE organs of sensation are the last portions of the bodies of insects 

 that we have to examine, and at the same time also the most simple; 

 for the commerce of insects with the external world, although consi- 



