. The biology of the amphibia. Amphibians. THE INTEGUMENT 133 do not appear until shortly before metamorphosis. The granular glands become surrounded by a muscular sheath of epidermal origin, while the mucous glands in various species remain without this cover. Both lie, for the most part, in the corium which during development increases in thickness and differentiates into three layers, the inner and outer layer being more compact than the middle one. Besides glands, connective tissue, and blood vessels, there is considerable smooth muscle in the Fig. 49.—Vertical section of the skin
. The biology of the amphibia. Amphibians. THE INTEGUMENT 133 do not appear until shortly before metamorphosis. The granular glands become surrounded by a muscular sheath of epidermal origin, while the mucous glands in various species remain without this cover. Both lie, for the most part, in the corium which during development increases in thickness and differentiates into three layers, the inner and outer layer being more compact than the middle one. Besides glands, connective tissue, and blood vessels, there is considerable smooth muscle in the Fig. 49.—Vertical section of the skin from the dorsal surface of the tail base of Plethodon cinereus showing three types of skin glands. Cap., capillary; D., dermis; Dt., duct of exhausted granular or poison gland; E., epidermis; , hedonic gland (cut to one side of main axis); , mucous gland; P., melano- phore; , poison gland; , developing poison gland. Poison Glands.—The granular glands of Amphibia protect their owner from being devoured by many possible enemies. The western newt, although terrestrial for a large part of the year, is rarely eaten by either birds or mammals (Storer, 1925). The poisonous properties of the glands have been studied critically, especially in European and South American Salientia (Phisalix, 1922), but these properties do not always protect many toads and salamanders from being eaten by snakes or even by other Amphibia. Secretion from both the mucous and the granular glands of many species is poisonous. Phisalix (1918) found that the mucus of Hydromantesitalicus when injected into a frog was more poisonous than the secretion of the granular glands. Nevertheless, the chief function of the mucous glands is to keep. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Noble, Gladwyn Kingsley, 1894-194
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
