CUTANEOUS QLA.NDS. 



77 



tubule, into which projects a coil of arterial blood vessels known as 



the gloinerulus (fig. 72). 



Very generally the outer body 

 surface is the seat of special secre- 

 tions which frequently play an impor- 

 tant part in the economy of the 

 animal, and are used especially as a 

 means of protection and defence. The 

 same is true also of the secretions of 

 the accessory glands opening into the 

 anterior or posterior end of the ali- 

 mentary canal (salivary glands, poison 

 glands, anal glands) (fig. 73). 



To the class of cutaneous glands 

 belong, in the first place, the sweat- 

 glands and the sebaceous glands of 

 Mammalia. The fluid secretion of the 

 former, on account of the ease with 

 which it is evaporated, is of special use 

 in keeping the body cool, while that 

 of the latter keeps the integument and 



FIG. 71. Diagrammatic represen- 

 tation of the kidney (segmental 

 organs) of a dog-fish embryo (after 

 C. Semper). Wtr, ciliated funnels ; 

 Ug, kidney duct. 



7> 



its special coveringsoft and supple. 

 The coccygeal glands of water- 

 birds are derived from an aggre- 

 gation of sebaceous glands ; their 

 secretion by keeping the feathers 

 oiled preserves them from becom- 

 ing saturated with water during 

 swimming. 



The unicellular and rnulticell- 

 ular integumentary glands, which 

 are found so widely present in 

 Insects, belong, for the most part, to the category of oil and fat 

 glands. Aggregations of cells whose function is to secrete calcareous 

 matters and pigment are especially widely present in the integu- 

 ment of the Mollusca, and serve for the building up of the beautifully 



FIG. 72. Ciliated funnel and Maliughian 

 body from, the anterior part of the kidney 

 of Proteus (after Spengel). Nr, kidney 

 tubule; Tr, ciliated funnel; Mk, Malpig- 

 hian body. 



