PHYLUM CHORDATA 



429 



When the embryo escapes from the egg by the rupture of 

 the egg-membrane it swims about as a little fish-like creature 

 or tadpole, with two pairs of branched external gills and a 



KlG. 237. — Rana esculenta. Urinogenital organs of the female. N, kidneys; 

 Od, oviduct; Ot, its coelomic aperture; Ov, left ovary (the right is removed); 

 P, cloacal aperture of oviduct; 5. S' , cloacal apertures of ureters; Ut, uterine 

 dilatation of oviduct. (From Wiedersheim's Comparative Anatomy.} 



long tail. There is no mouth, and eyes have not yet become 

 developed. On the lower surface of the head is a pair of 



