fUE REPRODUCTIVE ORGANS. 95 



The Wolffian bodies make their appearance very early, on 

 each side of the ventral aspect of the si3inal region of the em- 

 bryOy as small transversely-disposed tubuli, opening into a duct 

 which lies upon their outer side, and enters, posteriorly, into 

 the base of the allantois, and thence into the primitive cloaca 

 with which that structure is connected. The Wolffian duct is 

 one of the first-formed structures in the embryo, and precedes 

 the tubuli. 



The Kidneys appear behind the Wolffian bodies, and, ap- 

 parently, independently of them ; their ducts, the ureters^ are 

 also distinct, but likewise terminate in the pelvic part of the 

 allantois. Thus the urinary secretion passes into the allantois, 

 and it is that portion of this organ which lies within the abdo- 

 men, and becomes shut oif from the rest by the constriction 

 and obliteration of the cavity of an intermediate part, and its 

 conversion into the uraclms^ that gives rise to the urmary 

 bladder. The ultimate secreting tubuh of both the Wolffian 

 body and the kidney, are alike remarkable for ending in dila- 

 tations which embrace convoluted capillaries — the so-called 

 Malpightan tufts. Neither Wolffian bodies nor kidneys have 

 been observed in Amphioxus. It is doubtful whether true 

 kidneys are developed in Iclithyopsida^ or whether the so- 

 called kidneys of these animals are not, rather, persistent Wolf- 

 fian bodies. 



The Reproductive Organs. — These, in vertebrated animals, 

 are primitively similar in both sexes, and arise on the inner 

 side of the Wolffian bodies, and in front of the kidneys, in the 

 abdominal cavity. In the female the organ becomes an ovari- 

 um. This, in some few fishes, sheds its ova, as soon as they 

 are ripened, into the peritoneal cavity, whence they escape by 

 abdominal pores, wliich place that cavity in direct communi- 

 cation wdth the exterior. In many fishes, the bvaries become 

 tubular glands, provided with continuous ducts, which open 

 externally, above and behind the anus. But, in all other Ver- 

 tehrata, the ovaries are glands without continuous ducts, and 

 which discharge their ova from sacs, the Graafian follicles, 

 successively developed in their solid substance. Nevertheless, 

 these ova do not fall into the peritoneal cavity, but are con- 

 veyed away by a special apparatus, consisting of the Fallopian 

 tubes, which result from the modification of certain embryonic 

 structures called the MiXllerian ducts. 



The Miillerian ducts are canals which make their appear- 

 ance alongside the ducts of the Wolffian bodies, but, through- 



