Endopterygote Metamorphosis

In more primitive endopterygotes such as Neuroptera and Coleoptera, as in exoptery-gotes, a good deal of progressive development of organ systems occurs during larval life so that metamorphosis, relatively speaking, is slight and concerns, again, mainly the flight mechanism. At the opposite extreme, seen in many Diptera and Hymenoptera, most larval tissues are histolyzed, with adult tissues being formed anew, often from specific groups of undifferentiated cells, the imaginal discs and abdominal histoblasts. The imaginal discs occur as thickened regions of epidermis whose cells remain embryonic; that is, in the larval instars their differentiation is suppressed by the hormonal milieu existing in the insect at this time. At metamorphosis striking changes occur in the concentration of certain hormones, as a result of which the cells can multiply and differentiate into specific adult organs and tissues (Figure 21.9). Experiments in which cells have been selectively destroyed by X-irradiation have shown that formation of imaginal discs occurs very early in embryogenesis and at specific sites. Furthermore, each imaginal disc differentiates in a predetermined manner. During larval development, the discs grow exponentially in relation to general body growth and, typically, come to lie within an invagination, the peripodial cavity, beneath the cuticle (Figure 21.11). In contrast to the imaginal discs, the abdominal histoblasts, which

FIGURE 21.9. Imaginal discs of Drosophila and their derivatives in the adult body. [From H. Wildermuth, 1970, Determination and transdetermination in cells of the fruitfly, Sci. Prog. (Oxford) 58:329-358. By permission of Blackwell Scientific Publications.]

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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