Chapter

518 openings so that the pericardial sinus is in effect continuous with the perivisceral sinus.

Ventrally, a perineural septum (ventral diaphragm) may occur, which cuts off the perineu-ral sinus from the perivisceral sinus. Generally, the ventral diaphragm is restricted to the abdomen and occurs only in species whose ventral nerve cord extends into this region of the body (Miller, 1985). It is capable of performing posteriorly directed undulations and may have openings. It may receive motor nerves from segmental ganglia, which regulate the rate at which it undulates, though the undulations originate myogenically. In some insects, for example, caddisflies and cockroaches, the ventral diaphragm is reduced to a few transverse or longitudinal muscles, respectively. Frequently, there is a close physical association between the diaphragm (or its vestiges) and the nerve cord. Thus, in cockroaches and Pseudaletia unipuncta the actions of the longitudinal muscle remnants cause the nerve cord to oscillate laterally, bringing it into greater mix with the hemolymph and possibly improving hemolymph flow (Koladich et al., 2002). Hemolymph circulation through the legs and palps of some insects is assisted by the presence of a longitudinal septum that partitions the appendage into afferent and efferent sinuses.

To further facilitate hemolymph flow, especially through appendages, accessory pulsatile organs (auxiliary hearts) commonly occur (Pass, 1998, 2000). These have been identified in the head, antennae, thorax, legs, wings, and ovipositor. In many species they are saclike structures that have a posterior incurrent ostium and an anteriorly extended vessel. In antennal pulsatile organs the vessel may run the length of the appendage but is perforated at intervals to permit exit of hemolymph. The wall of the sac may be muscular, so that constriction of the sac is the active phase, and dilation results from elasticity of the wall, or the sac may have attached to it a discrete dilator muscle, and constriction is due to the sac's elasticity. In some situations, for example, the legs of Orthoptera and Hemiptera, the accessory pulsatile organ is simply one or two small muscles that attach to the longitudinal septum. Indeed, in Hemiptera, the organ is clearly derived from a skeletal muscle, the pre-tarsal depressor (Figure 14.5C) (Hantschk, 1991). Contraction narrows the efferent sinus, while enlarging the afferent sinus. Valves ensure that hemolymph is pushed toward the limb tip, then back toward the body cavity. Normally, accessory hearts are quite separate from the dorsal vessel, though in some Odonata they are connected via short vessels with the aorta into which they pump hemolymph. Most accessory pulsatile organs are not innervated.

Hemopoietic organs have been described for a number of insects. For example, in Gryllus there are pairs of such organs, in the second and third abdominal segments, directly connected with the dorsal vessel. Like those of vertebrates, the hemopoietic organs serve both as the site of production of at least some types of hemocytes and as centers for phagocytosis. The same cells within the hemopoietic organ can carry out both of these functions, though not simultaneously; thus, during periods of infection, division of the cells to form new prohemocytes is greatly retarded.

At specific locations in the circulatory system are sessile cells, usually conspicuously pigmented, called athrocytes (Locke and Russell, 1998). They occur singly, in small groups, or form distinct lobes, and are always surrounded by a basal lamina, a feature that distinguishes them from hemocytes. In most species athrocytes are situated on the surface of the heart (occasionally also along the aorta), and these are referred to as pericardial cells. They may also be found as scattered cells in the fat body (in Lepisma), in clusters at the bases of legs (in Gryllus and Periplaneta), or as a garland of cells around the esophagus (in some larval Diptera). When mature they may contain several nuclei, as well as mitochondria, Golgi apparatus, and pigment granules or crystals of various colors. The cells are able to accumulate colloidal particles, for example, certain dyes, hemoglobin, and chlorophyll,

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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