. Comparative anatomy. Anatomy, Comparative. 448 COMPARATIVE ANATOMY proper medical treatment. Today, however, as a result of the discovery of insulin and the part it plays in life, thousands of people who a generation ago were destined to prolonged suffering and premature death are able to live a fairly normal life. Pancreatic islands occur in all classes of vertebrates, usually in con- nexion with the pancreas, though in some bony fishes the two glands are Blood vessel Al\ eoli^. Fig. 374.—An island of the pancreas with the stirrounding alveoli, from an adult. X400. (From Bremer's "Text
. Comparative anatomy. Anatomy, Comparative. 448 COMPARATIVE ANATOMY proper medical treatment. Today, however, as a result of the discovery of insulin and the part it plays in life, thousands of people who a generation ago were destined to prolonged suffering and premature death are able to live a fairly normal life. Pancreatic islands occur in all classes of vertebrates, usually in con- nexion with the pancreas, though in some bony fishes the two glands are Blood vessel Al\ eoli^. Fig. 374.—An island of the pancreas with the stirrounding alveoli, from an adult. X400. (From Bremer's "Text Book of ;) independent. Both arise from the endoderm, but there is no evidence that pancreatic gland cells are ever converted into cells of the blood-islands. THE GONADS Male Sex Glands. The structure and development of the male gonads have already been described in detail. We are now concerned with their endocrinal function. It has long been known that removal of the gonads in childhood prevents the appearance of secondary sex characters of the male, such as beard, deeper voice, broadened shoulders, etc., the castrated individual becoming a eunuch and lacking the virile traits of the normal male. Evidently, then, the appearance of those traits which distinguish male from female depends upon some physiological action of the testes. That this is an endocrinal effect of the interstitial Leydig cells of the testes and not of the seminiferous tubules which produce the spermatozoa, may be inferred from the fact that male traits develop in the absence of the seminiferous tubules, provided only that the interstitial tissue is. 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 Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's So
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