Introduction

The circulatory system of insects, like that of all arthropods, is of the "open" type; that is, the fluid that circulates is not restricted to a network of conducting vessels as, for example, in vertebrates, but flows freely among the body organs. An open system results from the development, in evolution, of a hemocoel rather than a true coelom. A consequence of the open system is that insects have only one extracellular fluid, hemolymph, in contrast to vertebrates, which have two such fluids, blood and lymph. The occurrence of an open system does not mean that hemolymph simply bathes the organs it surrounds because usually thin granular membranes separate the tissues from the hemolymph itself. Insects generally possess pumping structures and various diaphragms to ensure that hemolymph flows throughout the body, reaching the extremities of even the most delicate appendages. As the only extracellular fluid, it is perhaps not surprising that the hemolymph, in general, serves the functions of both blood and lymph of vertebrates. Thus, the fluid fraction (plasma) is important in providing the correct milieu for body cells, is the transport system for nutrients, hormones, and metabolic wastes, and contains elements of the immune system, while the cellular components (hemocytes) provide the defense mechanism against foreign organisms that enter the body and are important in wound repair and the metabolism of specific compounds.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook


Post a comment