2S AN INTRODUCTION TO ENTOMOLOGY. 



a large part of the muscular system will be exposed to view. Plate 

 I. i. is the thorax and abdomen of a larva \vhich has been pre- 



pared in this way. In the^ the band-like structure- repre- 



ss lining the body-wall are muscles. And the number is much 

 greater than >hown here; for between these muscles and the body- 

 wall there are in most places several layers of diagonal muse! 



The muscif. :n is composed of an immense number of dis- 



tiiu d, straight fibres, which are alw.r not inclosed 



in tendinous sheaths as with Vertebrates). As a rule, the muscles 

 that move the segments of the body are not furnished %v ith tendons 

 -. hile those that move the appendages are thus united at 

 the distal end (Fig. 38). In appearance the muscles are either 



FIG. 38. Leg of May-beetle. (After Straus-Durckheim.) 



colorless and transparent, or yellowish white ; and of a soft, almost 

 gelatinous consistence. When properly treated with histological 

 reagents, and examined with a microscope of moderately high 

 they present numerous transverse striations, like the volun- 

 tary muscles of Vertebrates. 



The Alimentary Canal. In the ideal figure given on page 25, the 



alimentary canal is represented as a straight tube extending from 



ihe body to the other. In the larva of some insects there 



n approach to this degree of simplicity. Hut usually the tube is 



longer than the body, and is consequently more or less convoluted. 



Moreover, it is not of uniform structure, but, as in the higher animals. 



diff. are adapted to different functions. Names 1. 



:i applied to these special parts similar to those used to desig- 



nat ilogous parts in higher animals. These are as follows : 



There is within the head a portion of the alimentary canal that 



ually more or less enlarged; this is the pharynx. It ha> been 



shown recently * that in some sucking inserts the pharynx is fur- 



-vith powerful m by which it can be distended, and 



the pumping organ, by which these in^ 



Edwaid Burgess, Contributions to the Anatomy of tin- Milkwce.d Butterfly (Me- 

 moirs of the Boston Society of Natural History, 1880). 



ire Dimmock, The Anatomy of the Mouth-parts and Sue Id tusof some 



Diptcra (Boston, 1881). 



