INTEGUMENT. 71 



free edge are known as the cycloid, and those with a comb-like 

 edge the ctenoid scales. When the scales are of a small size 

 and irregular form, they are called placoid, but when large 

 and tesselated, ganoid. The minute anatomy of the two last 

 varieties may more or less closely resemble that of tooth or 

 bone. All fishes have an abundant mucoid product thrown 

 off from the cellular sub-epidermic la} r er. It is especially 

 abundant about the gill covers and along the ' lateral line/ 

 and is everywhere exceedingly copious in Anyuilla (eel), with 

 which the scales are rudimentary. 



Batrachia. Integument loosely attached to muscle, and is 

 without scales, rarely with plates, as in extinct Labyrintho- 

 don. In Eana (frog) the whole surface of the epidermis is 

 beset with minute trifid apertures leading to spherical sacs. 

 (Huxley.) 



Reptilia. Integument never scaled ; often tuberculate, 

 or epidermis assuming form of tesselated plates, as in Chelo- 

 nia. In Ophidia and Sauria the epidermic plates are more 

 or less laminated. During process of shedding skin, which 

 occurs periodically with Ophidia, the epithelial layer is 

 thrown off entire. No glandular appendages. 



Aves. Integument loosely connected to muscle, and cov- 

 ered with feathers, q.v. Horny beak, spur, and tesselated 

 plates to tarsi, are examples of cuticular development. 

 \Yhile papillse of derm may be pronounced, glandular ap- 

 pendages are absent. 



Mammalia. Derm well developed; papilla generally 

 small, large on the pads of feet, or on muzzle. Epidermis 

 rarely forming a connected layer, as on tail of Castor (beaver), 

 in bone-like plates, as in Dasypus (armadillo), or in laminated 

 processes, as in Manis (pangolin). 



Nails are flattened, horny plates developed from the upper 

 surface of the phalangeal integument only, as in many mon- 

 keys and man. Claws are nails which embrace a larger 

 portion of the phalanx, being developed not merely from its 

 upper surface, but also from its extremity, and extending far 

 round on its sides, as in carnivores. In the dog and cat a 

 bony plate extends from last phalanx into the posterior fold 



