Embryonic Development

system by growing along the surface of pioneer neurons (Section 7.3) or neurons of previ- 609

ously formed sensilla (Heming, 2003). Similarly, both compound and simple eyes develop from groups of epidermal cells, each of which divides and differentiates to form the pho-toreceptive and accessory components of the light-sensitive structures.

Imaginal discs and histoblasts, from which many adult tissues are derived at metamorphosis in higher Diptera and Hymenoptera (Chapter 21, Section 4.2), can be recognized soon after germ-band formation. They are groups of cells that separate from the ectoderm in characteristic numbers, sizes and shapes, at specific sites in the body (Heming, 2003).

Concurrently with the formation of abdominal appendages a number of ectodermal invaginations develop, from which differentiate endoskeletal components, various glands, the tracheal system, and certain parts of the reproductive tract (for the latter, see Section 7.6). From ventrolateral invaginations at the junctions of the antennal/mandibular segments and the mandibular/maxillary segments are derived the anterior and posterior arms of the tentorium. Paired mandibular apodemes differentiate from invaginations near the bases of the mandibles. The apodemes of the trunk region arise from intersegmental invaginations in the thorax and abdomen.

Salivary glands develop from a pair of invaginations near the bases of the labial appendages. When the appendages fuse the invaginations merge to form a common salivary duct that opens midventrally on the hypopharynx.

The corpora allata develop from a pair of ventrolateral invaginations at the junction of the mandibular/maxillary segments. Initially, they exist as hollow vesicles, though these fill in as they move dorsally to their final position adjacent to the stomodeum. The molt glands also originate as paired ventral ectodermal invaginations, usually on the prothoracic segment. Although the endocrine glands arise before katatrepsis, at this time they are non-secretory, and maternally derived hormones (especially ecdysteroids) stored in the egg are used in embryonic endocrine regulation (Section 9). Other invaginations on the head may give rise to specialized exocrine glands on the mandibles or maxillae.

Elements of the tracheal system can be seen first as paired lateral invaginations on each segment from the second thoracic to the eighth (ninth in a few Thysanura) abdominal. However, not all of these invaginations develop completely into tracheae. Those that do, bifurcate and anastomose with branches from adjacent segments and from their opposite partner of the same segment. The cells differentiate as tracheal epithelium and then secrete a cuticular lining. After cuticle secretion but before hatching, gas is secreted into the tracheal system. Some of the invaginated ectodermal cells differentiate into oenocytes. These may remain closely associated with the tracheal system, form definite clusters in specific body regions, or become embedded as single cells in the fat body.

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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