308 ZOOLOGY sect. 



traversing the capillaries of the liver, being returned by the 

 hepatic vein into the post-caval. 



The red corpuscles are oval and nucleated, and are remarkable 

 for their unusual size. Those of Amphiuma are the largest 

 known, being about y\ mm. in diameter, or eight times that of a 

 human red corpuscle. 



Nervous System and Sense-Organs. — The train of Urodela 

 differs from that of the Frog in its more elongated and slender 

 form, in the comparatively small size of the optic lobes, and in the 

 non-union of the olfactory lobes. The olfactory sacs always open 

 into the mouth by posterior nares situated behind or external to 

 the vomers. The eye has no lids in the lower forms and is de- 

 generate in the cave-dwelling Proteus and in some Gymnophiona. 

 The Urodela, the Gymnophiona, and some Anura have no tympanic 

 cavity or membrane, and no columella ; there is, however, a stapes, 

 (Figs. 948, 949) in the form of a nodule of cartilage inserted in the 

 fenestra ovalis. In the perennibranchiate Urodeles and in the 

 larvae of the air-breathing forms lateral-line sense-organs are 

 present. There was an extensive lateral line system, leaving its 

 impress on the bones of the skull, in the Stegocephala. 



IJrindgenital Organs. — In the Urodela the kidneys (Fig. 955, 

 N) are much elongated and are divided into two portions, a broad 

 posterior part, the functional kidney {G-N), and a narrow anterior 

 sexual part connected in the male with the efferent ducts of 

 the testis. Numerous ducts leave the kidney and open into the 

 Wolffian (mesonephric) duct \lg. ( Ur.)\ which thus acts as a ureter 

 in the female, as a urinogenital duct in the male. The oviduct 

 [jiig. {Od.)'\ is developed from the Miillerian duct, a rudiment of 

 which {mg., mg'.) occurs in the male. In the Gymnophiona the 

 kidneys extend the whole length of the coelome, and in the young 

 condition are formed of segmentally arranged portions, each with 

 a nephrostome and a glomerulus, as in Myxinoids (see p. 141). 

 A pronephros is present in the larva, but disappears in the adult. 

 In some Gymnophiona the cloaca can be protruded and acts as a 

 penis. 



Reproduction and Development. — External impregnation 

 takes place in Anura, but in many Urodela the sperms are 

 aggregated into spermatophores by glands in the wall of the cloaca, 

 and these, being deposited on the body of the female, are taken 

 into the cloaca and effect internal impregnation. 



Several curious instances of parental care are known. A 

 number of different species of Frogs and Toads construct nests 

 or shelters of leaves or other materials in which the eggs are 

 deposited and in which the young are developed. In the Obstetric 

 Toad (Alytes ohstetricans) of Europe the male winds the strings 

 of eggs — formed by the adhesion of their gelatinous investment — 

 round his body and thighs, where they are retained until the 



