114 



STRUCTURE OF THE VERTEBRATES 



inherited. The hair has a possible homologue, but the skin glands 

 are unlike anything in the ancestral groups. In addition, most 

 orders have some epidermal modification which arose inde- 

 pendently. 



""Papilla 



Developmental Stages of Feather 



Scales 



Beak 



Head of Pigeon 



Homy beak 



Mouth 

 cavity 



Tongue 



-Mandible 



Cross Section of 

 Bird's Beak 



Fig. 50. Integumentary Structures of the Bird. The scales are homologous 



with the feathers. The horny beak is a modification that has appeared 



in other toothless forms. 



Scales 



Tail of White Rat 



Body Scales of Manis^ 



Fig. 51. Scales of the Mammal. Scales are usually limited to the tail 

 region in the Mammalia. Manis (Fig, 35) is covered with overlapping 



ectodermal scales. 



