352 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



gize the Mullerian ducts (oviducts) of elasmobranchs with those of 

 other forms. Still, when the adult conditions are considered — simi- 

 lar ostia, similarity of position and of external openings — it is hardly 

 possible to believe them as merely analogous, as examples of conver- 

 gence. The facts in the amphibia, referred to in the preceding 

 paragraph are additional evidence of homology. If, however, it be 



Fig. 375. — Diagrams of urogenital organs of female fishes, after Goodrich. A 

 Protopterus; B, Polypterus; C, Amia; D, Lepidosteus; E, most teleosts; F, salmonid. ap, 

 abdominal pore; cb, cloacal bladder; cl, cloaca;/, funnel of oviduct; gp, genital pore or 

 papilla; m, mesonephros; 0, ovary; od, oviduct; r, rectum; s, urogenital sinus; up, urinary 

 pore, (papilla) ; ugp, urogenital pore (papilla) ; w, Wolffian ducts. 



assumed that the more common type of development, by the infold- 

 ing of coelomic epithelium, be the primitive condition, the difl&culties 

 are less, though not entirely solved. Then, if it be that the homolo- 

 gous tissue in the elasmobranchs was at first included in the tissue of 

 the pronephric duct and that the splitting is a secondary operation to 

 separate parts which elsewhere are always distinct, the similarities are 

 more apparent. 



