9O MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



sometimes on the operculum, and sometimes in the axilla, but 

 always in connection with a strong spine. Of our native fishes 

 the poison glands in the axilla of certain catfishes (^Noturus) are 

 best known. In the toadfish (^Batrachus) a gland in similar 

 position is well known, but apparently its secretion is not 

 poisonous. 



In the amphibia, glands in the skin which secrete an acrid 

 juice are abundant, and in the toads their presence causes the 

 warty skin so noticeable in these animals. In the sauropsida, 

 glands are few in number. In certain snakes stink glands occur 

 in the skin, the secretions of which give these animals a dis- 

 agreeable odor. In the lizards, glands are found only on the 

 inside of the femoral region of the hind limbs, the openings of 

 which (femoral pores) are of considerable value in the classifi- 

 cation of these forms. In the birds, glands are developed on 

 the reduced tail (uropygial glands), the oily secretion of which 

 is used in oiling the feathers. These glands are best developed 

 in the water birds. In the rasores there are in addition glands 

 in the neighborhood of the eye. 



In the mammals, glands are well developed, and acquire a 

 great variety of form. These glands may be arranged in two 



categories, the tubular 

 and the racemose, the 

 characters of which 

 are indicated by their 

 names. To the tubu- 

 lar type belong the 

 sweat glands, which 

 extend deep into the 

 derma, and in their 

 deeper portions be- 

 come coiled and con- 

 voluted (Fig. 95). 



FIG. 96. Different types of glands, a, intesti- 

 nal epithelium with a gland- (goblet) cell; b, uni- 

 cellular gland with duct ; c, simple tubular gland ; 

 d, simple racemose gland ; e, compound racemose 

 gland. 



The racemose (acinose) glands, in their simplest condition, 

 form the sebaceous glands, and are normally placed in close 

 connection with the roots of the hair. In some mammals the 

 sebaceous glands of certain regions of the body become con- 

 verted into scent glands, the secretions of which may serve for 



