Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 IXTEGUi£ENT OF VERTEBRATA. 421 looks like an appendage of the gland. The sebaceous glands undergo the most various modifications in form, size^ and number^ as well as in the quality of their secretion. Both sets of glands frequently secrete odorous matters of various kinds, which play an important part in the economy of the animal. Glands of this kind are developed in the most diverse regions of the surface of the body in many orders of the Mammalia. § 323. The most important modification
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 IXTEGUi£ENT OF VERTEBRATA. 421 looks like an appendage of the gland. The sebaceous glands undergo the most various modifications in form, size^ and number^ as well as in the quality of their secretion. Both sets of glands frequently secrete odorous matters of various kinds, which play an important part in the economy of the animal. Glands of this kind are developed in the most diverse regions of the surface of the body in many orders of the Mammalia. § 323. The most important modification of the integu- mentary glands in all Mammals is the development of milk-secreting glands, which enter into relation to the reproduc- tive function. They are regularly, and, as a rule, symmetrically arranged on the ventral surface of the body. Each ' mammary gland ' consists of a complex of separate glandular tubes, the ducts of which are either quite separate or united together. In the Monotremata these organs differ but little from the other kinds of integumentary glands. Each of the two organs here present is made up of a group of tubes, which ^ -^ pass separately through the skin. The area on which they open is merely distinguished by the ab- sence of hairs, and in Ornithorhynchus is on the same level as the surrounding integument. In Echidna it is placed inapouch-like depression (mammary pouch), which appears to serve as a re- ceptacle for the young. In the rest of the Mammalia nipples are present; these are special arrangements which were gradually developed by the process of sucking, and which afford the young a more suitable connection with the mam- mary apparatus, while at the same time they make each complex of milk-glands distinguishable externally. There are two very different conditions of the perfected nipple. They are both preceded by a similarly indifferent stage (Fig. 217, A), in which a nearly flat glandular area (6) has a number Fig. 217. Diagram of tte d
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