HEX APOD A 35 



and attached to it, are represented a few of the muscles (ra); it will be 

 seen that these muscles are so arranged that the contraction of those on 

 the lower side of the body would bend it down, while the contraction of 

 those on the opposite side would act in the opposite direction. The 

 alimentary canal (a) occupies the centre of the body, and extends from 

 one end to the other. The heart (//) is a tube lying between the ali- 

 mentary canal and the muscles of the back. The central part of the 

 nervous system (n) is a series of small masses of nervous matter con- 

 nected by two longitudinal cords: one of these masses, the brain, lies in 

 the head above the alimentary canal; the others are situated, typically 

 one in each segment, between the alimentary canal and the layer of 

 muscles of the ventral side of the body; the two cords connecting these 

 masses, or ganglia, pass one on each side of the oesophagus to the brain. 

 The reproductive organs (r) lie in the cavity of the abdomen and open 

 near the caudal end of the body. The respiratory organs are omitted 

 from this diagram for the sake of simplicity. 



The muscular system. — We find in insects a wonderfully large number 

 of muscles. Those that move the segments of the body form several 

 layers just within the body-wall. The two figures on Plate II represent 

 two caterpillars which have been split open lengthwise, one on the middle 

 line of the back and one on the opposite side ; in each case the alimentary 

 canal has been removed, so that only those organs that are attached 

 quite closely to the body-wall are left. From a study of these figures 

 some idea can be obtained of the number and arrangement of these 

 muscles. It should be borne in mind, however, that only a single layer of 

 muscles is represented in these figures — the layer which would be seen 

 if a caterpillar were opened in the way indicated. When these muscles 

 are cut away many other muscles are found extending obliquely in 

 various directions between these muscles and the body-wall. 



The muscles of insects appear very differently from those (the lean 

 meat) of higher animals. In insects the muscles are either colorless and 

 transparent, or yellowish- white ; and they are soft, almost of a gelatinous 

 consistency. The fibers of insect muscles are usually if not always of the 

 striated type. 



As a rule, the muscles of insects are composed of many distinct fibres 

 which are not enclosed in ten- 

 dinous sheaths as with verte- 

 brates. But the muscles that 

 move the appendages of the 

 body are furnished with a ten- 

 don at the end farthest from the 



bnHv (Pier f\0>\ ^ IG ' ^ — ^eg °^ May-beetle. (After Straus-Durckheim.) 



Notwithstanding the soft and delicate appearance of the muscles 

 of insects, they are really very strong. 



The alimentary canal. — The typical position of this is represented in 

 the diagram (Fig. 67) ; and on Plate III, illustrating the anatomy of a 

 cockroach, its form in that insect is shown. In larvae it is a nearly 

 straight tube, extending from one end of the body to the other. But in 

 adult insects it is usually much longer than the body, and is consequently 

 more or less folded. It is composed of parts differing in form and use. 

 To these parts names have been given similar to those used to designate 

 the corresponding parts in higher animals; thus we distinguish a pharynx. 



