EXOSKELETON 



13 



teus (p. 11): some others have the body enclosed in an armor of 

 large plates, concerning the history of which little is known. In 

 other Teleosts there is far less regularity, peculiarities occurring in 

 Plectognaths, Lophobranchs and some Acanthopterygii, for details 

 of which reference should be made to systematic ichthyologies. 



DIPNOI. — In appearance at least, the scales of modern Dipnoi 

 are much like those of typical Teleosts. 



AMPHIBIA. — Scales are uncommon in modern Amphibia, but 

 were the rule in Stegocephals where they were usually restricted to 

 the ventral sides of the body, sometimes extending to the hmbs and 



WW 





^^ 



Fig. II. — Ventral plates of 

 Stegocephals (Credner in Zittel). 

 A, Branchiosaurus; B, details of 

 same; C, of Archegosanrus; D, of 

 Petrobates. 



Fig. 12.- — Section of skin of a body ring of 

 Epicrium (Sarasins, '87). b, basal layer of 

 corium; c, g, glands; e, epidermis; s, scales, the 

 black spots 'the squamulae; the head to the left. 



rarely to the back. Apparently scales of a cycloid appearance were 

 the most primitive and were arranged in oblique overlapping rows, 

 converging forwards (fig. ii). In the more specialized genera the 

 scales were slender and rod-like with gaps between the rows. It is 

 suggested that the gastralia of reptiles (p. i6) and at least some of 

 the plastral bones of turtles have been derived from scales similar 

 to the ventral armor of Stegocephals. 



Some Gymnophiones (fig. 12) have numerous scales embedded in 

 pouches in the skin, several scales in each pouch. Each scale is 

 two layered, the outer surface divided by reticulate lines into small 

 circular areas (squamulae) of uncertain significance. The scales are 



