Structure

The primary pump for moving hemolymph around the body is a middorsal vessel that runs more or less the entire length of the body (Figure 17.1). The posterior portion of the vessel has ostia (valves) and is sometimes known as the heart, whereas the cephalothoracic portion, which is often a simple tube, may be termed the aorta (Figure 17.1A). In some insects the heart is the only part that contracts, but in many others the entire vessel is contractile. The vessel is held in position by connective tissue strands attached to the dorsal integument, tracheae, gut, and other organs and by a series of paired, usually fan-shaped, alary muscles. Normally, the vessel is a straight tube, though in many species the aorta may loop vertically. Anteriorly the aorta runs ventrally to pass between the corpora cardiaca and under the brain. Generally the dorsal vessel is closed posteriorly; however, in Diplura,

FIGURE 17.1. (A) Ventral dissection of the field cricket, Acheta assimilis, to show dorsal vessel and associated structures; and (B) circulatory system of Campodea augens (Diplura) showing anterior and posterior arteries running off the dorsal vessel. [A, after W. L. Nutting, 1951, A comparative and anatomical study of the heart and accessory structures of the orthopteroid insects, J. Morphol. 89:501-597. By permission of Wistar Press. B, from a figure kindly supplied by Dr. Günther Pass.]

FIGURE 17.1. (A) Ventral dissection of the field cricket, Acheta assimilis, to show dorsal vessel and associated structures; and (B) circulatory system of Campodea augens (Diplura) showing anterior and posterior arteries running off the dorsal vessel. [A, after W. L. Nutting, 1951, A comparative and anatomical study of the heart and accessory structures of the orthopteroid insects, J. Morphol. 89:501-597. By permission of Wistar Press. B, from a figure kindly supplied by Dr. Günther Pass.]

Archaeognatha, Zygentoma, and some Ephemeroptera the dorsal vessel connects at its rear with arteries that run along the cerci and median caudal filament (Gereben-Krenn and Pass, 2000). In Diplura an artery also supplies each antenna (Figure 17.1B), and in Dictyoptera and some Orthoptera there are pairs of segmental arteries in the abdomen (Hertel and Pass, 2002). However, except as noted, in pterygotes circulation to appendages is achieved by means of accessory pulsatile organs and septa (see below).

In most insects the dorsal vessel is well tracheated. The heart may not be innervated or may receive paired lateral nerves from the brain and/or segmental ventral ganglia. Ostia may be simple, slitlike valves or deep, funnel-shaped structures in the wall of the heart, or internal

FIGURE 17.2. Incurrent ostia of Bombyx shown during diastole and systole. Arrows indicate direction of hemolymph flow. [After R. F. Chapman, 1971, The Insects: Structure and Function. By permission of Elsevier/North-Holland, Inc., and the author.]

flaps (Figure 17.2). Their position and number are equally varied. They may be lateral, dorsal, or ventral and may be as numerous as 12 pairs (in cockroaches) or as few as 1 pair (in some dragonflies). Ostia are usually incurrent, that is, they open to allow hemolymph to enter the heart but close to prevent backflow. In some orthopteroid insects, however, some ostia are excurrent. Histologically, the dorsal vessel in its simplest form comprises a single layer of circular muscle fibers, though more often longitudinal and oblique muscle layers also occur. Ultrastructural examination of the heart muscle cells reveals, however, that they contain, in addition to contractile elements, prominent Golgi complexes and vesicles, suggesting that the insect heart is secretory and, like that of vertebrates, may have a more significant role in homeostasis than just pumping hemolymph (Locke, 1989).

Assisting in directing the flow of hemolymph, especially in postlarval stages, are various diaphragms (septa) (Figure 17.3) that include both connective tissue and muscular elements. The spaces delimited by the diaphragms are known as sinuses. The pericardial septum (dorsal diaphragm) lies immediately beneath the dorsal vessel and spreads between the alary muscles. Laterally, it is attached at intervals to the terga and in most species has aorta aorta

ventral nerve cord

FIGURE 17.3. Diagrammatic transverse section through abdomen to show arrangement of septa. [From R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

ventral nerve cord

FIGURE 17.3. Diagrammatic transverse section through abdomen to show arrangement of septa. [From R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

FIGURE 17.2. Incurrent ostia of Bombyx shown during diastole and systole. Arrows indicate direction of hemolymph flow. [After R. F. Chapman, 1971, The Insects: Structure and Function. By permission of Elsevier/North-Holland, Inc., and the author.]

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.

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