|
|
|
|
|
|
|
|
|||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | |||||
Quarterly Journal of Microscopical Science, Vol s2-83, 91-139, Copyright © 1941 by Company of Biologists
1 Department of Entomology, Zoological Laboratory, Cambridge
The salivary glands of the Heteroptera consist of a pair of primarily bilobed principal glands and accessory glands which vary very greatly in form and structure in different families.
The glands are usually supplied with tracheae, and the principal glands are invested by a nervous plexus which is supplied by a glandular nerve from the hypocerebral ganglion of the stomatogastric system.
The principal salivary gland of Notonecta is characterized by the presence of large cells having zymogen granules and by the storage of fluid secretion in vacuoles. In contrast, most of the remaining Heteropteran salivary glands belong to the vesicular type, having a one-layered glandular epithelium made up of small cells which discharge their secretion into a large central storage cavity or axial canal. This type of gland lacks zymogen granules but has small dense masses of reserve material in the basal or outer parts of the cells. There is normally no difference in the structure of the glandular epithelium in the different lobes. The accessory glands are either in the form of a thin-walled bladder-like vesicle, or are tubular or duct-like; they seem to be purely a development of the primary conducting glandular system, and are thus homologous with the salivary reservoir of other orders. All the information obtained in this work is strongly against the idea that the various lobes of Hemipterous salivary glands produce widely different chemical substances, each with a special function. The results obtained by Fauré-Fremiet have not been confirmed.
Except with blood-sucking forms digestive enzymes were always found in the glands, two enzymes being the maximum number found in any particular gland. The enzymes were found to be always related to the type of food consumed, and were those concerned with the digestion of that particular component of the food which was present in the greatest proportion. In no case was a cellulase found. An anti-coagulant principle was found to be present in the glands of blood-sucking forms.
The accessory glands appear to produce only a watery secretion, enzymes being absent.
The pH of the principal gland is generally slightly acid, while that of the accessory gland is neutral.
Mitochondria and Golgi bodies typical of insect tissue are present in certain glands, but show no relation to the secretion granules, and thus do not appear to contribute to secretion synthesis.
From a number of experiments it appears that the action of the digestive enzymes is not sufficiently rapid for external digestion to take place to any great extent. It seems, however, certain that quite an appreciable quantity of the injected saliva is imbibed again, and that the salivary digestion continues in the stomach, where the food taken in is first stored.
The pH activity range of the enzymes is in general wide.
