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Chapter 3 INTERNAL ANATOMY AND PHYSIOLOGY What you see if you dissect open the body of an insect is a complex and compact masterpiece of functional design. Figure 3.1 shows the “insides” of two omnivorous insects, a cockroach and a cricket, which have relatively unspecialized digestive and reproductive systems. | TIC03 5 20 04 4 48 PM Page 49 Chapter 3 INTERNAL ANATOMY AND PHYSIOLOGY Internal structures of a locust. After Uvarov 1966. TIC03 5 20 04 4 48 PM Page 50 50 Internal anatomy and physiology What you see if you dissect open the body of an insect is a complex and compact masterpiece of functional design. Figure 3.1 shows the insides of two omnivorous insects a cockroach and a cricket which have relatively unspecialized digestive and reproductive systems. The digestive system which includes salivary glands as well as an elongate gut consists of three main sections. These function in storage biochemical breakdown absorption and excretion. Each gut section has more than one physiological role and this may be reflected in local structural modifications such as thickening of the gut wall or diverticula extensions from the main lumen. The reproductive systems depicted in Fig. 3.1 exemplify the female and male organs of many insects. These may be dominated in males by very visible accessory glands especially as the testes of many adult insects are degenerate or absent. This is because the spermatozoa are produced in the pupal or penultimate stage and stored. In gravid female insects the body cavity may be filled with eggs at various stages of development thereby obscuring other internal organs. Likewise the internal structures except the gut of a well-fed late-stage caterpillar may be hidden within the mass of fat body tissue. The insect body cavity called the hemocoel haemocoel and filled with fluid hemolymph haemolymph is lined with endoderm and ectoderm. It is not a true coelom which is defined as a mesoderm-lined cavity. Hemolymph so-called because it combines many roles of vertebrate blood hem haem and lymph bathes all internal organs delivers nutrients removes metabolites and performs immune functions. Unlike vertebrate blood hemolymph rarely has respiratory pigments and therefore has little or no role in gaseous exchange. In insects this function is performed by the .
