254 Genetic Interpretations in the Domain of Anatomy 



glands, which shall be based upon their genesis and upon the morpho- 

 logical distinctions, which exist between them. To begin with, we may 

 put the unicellular glands, of which the goblet-cells serve as the most 

 familiar type known in man, in the Class A, v. p. 25G; next we may have 

 the true multicellular glands of the epithelial type, which always develop 

 with ducts by which their secretion is discharged; these form Class B; 

 while a third class would include the false glands which never develop 

 with ducts, which produce either merely an internal secretion so-called, 

 or are adapted to the development of cells of special kinds, as, for ex- 

 ample, the lymph- and genital-glands; such structures constitute Class C. 



We must first attempt a classification more in detail of the true epi- 

 thelial glands (Class B). In my opinion Ave can best make two funda- 

 mental divisions. The glands of the first division have often been called 

 single or simple follicular glands ; I propose for them the term " simple 

 glands." The glands in question are always small and have one or several 

 centers of growth according as they are simple tubes or slightly branching. 

 Those of each kind are always very numerous and they occur more or less 

 near together over considerable areas. There are two types of these 

 known. The first are simple invaginated areas with scattered unicellular 

 glands, as for instance the glands of the large intestine, the so-called 

 Lieberkiihn's follicles; they might be called simple follicles. Glands of 

 the second type are invaginated areas with specialization of the cells, as, 

 for example, the sweat, gastric, and sebaceous glands; they might be called 

 glandular follicles. In the accompanying table the principal glands of 

 this division are enumerated. 



The glands of the second division are of greater bulk and are often 

 referred to as organic or branching glands. I propose to name them 

 " compound glands." They are provided with a single main duct, 

 which is more or less freely branched, each branch connecting finally with 

 the secretory portion proper of the organ, which portion may itself also 

 be branched or not. Each gland falling in this division is a more or less 

 complete organ by itself, receiving its special blood supply, and its special 

 innervation — is, in short, a clearly marked physiological entity. Such a 

 gland differs profoundly in its plan of organization from the glands of 

 our first division. Of the second division there are clearly three main 

 types to be distinguished. In the first type the branches of the glands 

 are found to be supported by mesenchyma or its derivative, connective 

 tissue, which is more or less abundant between the ducts and secretory 

 elements of the organ, and in the mesenchyma there is a capillary circu- 

 lation, which is often brought, however, into.. intimate proximity with 

 the epithelial elements of the organ. These organs are further character- 



