IV. VERTEBRATA: AMPHIBIA. 



517 



some time on account of the respiratory mechanism. This renders 

 intelligible the fact that many Salamandrina (Spclcrpcs, Desmognathus, 

 Plet/iodon, Gyrinop/iilus, etc.) have neither gills nor lungs, but have only 

 pharyngeal and cutaneous respiration. The capillary network in these 

 parts is greatly developed and may extend into the epithelium. Thus, 

 also, it happens that in the Anura the skin receives as large an artery 

 as the lungs (fig. 570, en). 



The skin is thin and slimy from the numerous mucous glands, which 

 not infrequently produce a poisonous secretion (so called parotid gland in 

 the ear region). The epithelium bears a thin horny layer which at in- 

 tervals is molted as a continuous sheet. The corium in the Anura is 



FIG. 569. FIG. 570. 



FIG. 569. Heart and arterial arches of salamander larva (after Boas), a 1 a 2 

 right and left auricles; aa, arterial trunk; ad, dorsal aorta; as, left aortic arch; b, direct 

 connection between afferent and efferent arteries ;c, carotid;/, afferent artery ;/>, pulmon- 

 ary artery; v, ventricle; 1-4, afferent arteries; I'-T,', gills. 



' FIG. 570. Heart and arches of frog (diagram), a, a a , right and left auricles; aa, 

 ventral aorta; ad, as, right and left aortic arches (radices aorta?) ; c, carotid ; r, cutaneus; 

 /, lingualis; p, pulmonary artery; ss, subclavian; v, ventricle; ve, vertebralis; i, 2, 4, 

 persisting arches. 



undermined by large lymph spaces, the presence of which makes the 

 skinning of a frog such an easy matter. Ossifications in the skin enor- 

 mously developed in the fossil Stegocephali occur but rarely (Gymno- 

 phiona) in recent Amphibia. On the other hand, the abundance of 

 chromatophores is noticeable, these, under the influence of the nerves, 

 changing their shape and thus producing color changes in many Amphibia. 

 Theheart (figs. 569, 5 70) has two auricles, distinctly separated in Anura, 

 a right with venous blood, a left which with pulmonary respiration re- 

 ceives arterial blood. There is, however, but a single ventricle, and the 



