External Structure

FIGURE 3.5. Relationship of the tentorium to grooves and pits on the head. Most of the head capsule has been cutaway. [From R. E. Snodgrass. Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

The tentorium (Figure 3.5) is an internal, cranial-supporting structure whose morphology varies considerably among different insect groups. Like the furca of the thoracic segments (Section 4.2), with which it is homologous, it is produced by invagination of the exoskeleton. Generally, it is composed of the anterior and posterior tentorial arms that may meet and fuse within the head. Frequently, additional supports in the form of dorsal arms are found. The latter are secondary outgrowths of the anterior arms and not apodemes. The junction of the anterior and posterior arms is often enlarged and known as the tentorial bridge or corporotentorium. In addition to bracing the cranium, the tentorium is also a site for the insertion of muscles controlling movement of the mandibles, maxillae, labium, and hypopharynx.

The grooves described above delimit particular areas of the cranium that are useful in descriptive or taxonomic work. The major areas are as follows. The frontoclypeal area is the facial area of the head, between the antennae and the labrum. When the epistomal sulcus is present, the area becomes divided into the dorsal frons and the ventral clypeus. The latter is often divided into a postclypeus and an anteclypeus. The vertex is the dorsal surface of the head. It is usually delimited anteriorly by the arms of the epicranial suture and posteriorly by the occipital sulcus. The vertex extends laterally to merge with the gena, whose anterior, posterior, and ventral limits are the subocular, occipital, and subgenal sulci, respectively. The horseshoe-shaped area lying between the occipital sulcus and postoccipital sulcus is generally divided into the dorsal occiput, which merges laterally with the postgenae. The postocciput is the narrow posterior rim of the cranium surrounding the occipital foramen. It bears a pair of occipital condyles to which the anterior cervical sclerites are articulated. Below the gena is a narrow area, the subgena, on which the mandible and maxilla are articulated.The labium is usually articulateddirectlywith the neck membrane (Figure 3.3C), but in some insects a sclerotized region separates the two. This sclerotized area develops in one of three ways: as extensions of the subgenae which fuse in the midline to form a subgenal bridge, as extensions of the hypostomal areas to form a hypostomal bridge, or

(in most prognathous heads) through the extension ventrally and anteriorly of a ventral cervical sclerite to form the gula. At the same time the basal segment of the labium may also become elongated (Figure 3.4A).

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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