XIII 



PHYLUM CHORDATA 



287 



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

 human red corpuscle. 



Nervous System and Sense Organs. The brain 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 



8c> 



FIG. 900. Diagrams of urinogenital organs of male (A) and female (B) Urodele. a, collecting 

 tubes ; GN, sexual portion of kidney ; Ho, testis ; Ig. (Ur.) Wolffian duct (ureter); mg, mg', 

 vestigial Mullerian duct of male ; mg. (Od\ oviduct ; N, non-sexual portion of kidney ; 

 Ov. ovary; Ve, vasa efferentia; t, longitudinal canal. (From Wiedersheim's Comparative 

 Anatomy, after Spengel.) 



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, 



