Both the original material and the data from literature collected in two previous papers, show a considerable diversity of structure and secretion of the glands which constitute the hepatoid gland type. According to the body of available histological (including morphometrical) and histochemical data, the authors distinguish: a) features characteristic of the hepatoid gland type only which do not appear in other types of skin glands; b) seven histological varieties within the hepatoid gland type. These seven varieties can be united, according to the laws of their structure and function, into two groups (1-3 and 5-7), with an intermediate variety (4) between them. The first group includes hepatoid glands of the "classical" structure which has been previously detaily exampled by circumanal glands of the dog: these glands possess cysts, produce a purely protein secretion; the secretion type is merocrine. The second group comprises mero-holocrine hepatoid glands which are characterized by the absence of cysts, broader excretion ducts, and a capability to produce, besides protein, considerable amounts of melanin and/or hydrophobic lipids.
