r /HE INTEGUMENT AND THE EXOSKELETON 113 



iluid, these glands are usually called. sweat glands (glandules 

 mdoriparce), but enough has been said to show that this term 

 is too limited to be employed in general. In Man, where they 

 fulfill this function, they do not appear to be evenly distributed, 

 and there seem to be individual differences in the extent and 

 copiousness of the secretion. As it has been found that these 

 glands rarely occur in the integument of the Fuegians, there 

 are undoubtedly marked racial differences, but there is, at 

 present, little knowledge upon this point. 



The primary use of the second, or acinous, type of integu- 

 mental gland seems to be to furnish an oily secretion for the 

 lubrication of the hair, forming the sebaceous glands; and cor- 

 responding to this use, they appear less inclined than does the 

 other type to become disassociated from a hair follicle. 

 Modified forms do occur, however, often unconnected with 

 hair follicles, and modified in their secretion to subserve some 

 special use. Such are the tar sal \_meibomian'] glands of the 

 eyelid, which are properly the hypertrophied sebaceous glands 

 of the eyelashes, whose purpose it is to supply a line of oil for 

 the edges of the lids and thus prevent the overflow of tears. 

 Other modified forms of this type are found at the orifices of 

 the body, as the lips, the anus, and upon the external genitals 

 (Tyson's glands, prepntial glands, etc.). Corresponding to 

 their primary function as sebaceous glands, they are wanting 

 in Cetacea and in adult Sirenia ; the scale-covered Manis retains 

 only the modified orificial glands. They are, however, wholly 

 wanting in some sloths (Cholcepus) and in an African insec- 

 tivore (Chrysochloris), the same animals in which the glands 

 of the tubular type are also wanting. 



Aside from these small, generally distributed, glands, the 

 integument of mammals is especially characterized by the oc- 

 currence of localized masses of glands, often voluminous in 

 size and furnishing a secretion intended for a special purpose. 

 The elements of which these masses are composed are some- 

 times of the tubular and sometimes of the acinous type, or of 

 both sorts together. Of these the anal sacs are widely dis- 

 tributed, composed mainly of tubular glands, and forming 



