106 THE ANATOMY OF VERTEBEATED ANIMALS. 



a duct which lies upon their outer side, and enters, poste- 

 riorly, 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 Wolfiian bodies, and, appa- 

 rently, 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 allan- 

 tois, and it is that j)ortion of this organ which lies within 

 the abdomen, and becomes shut ofi" from the rest by the 

 constriction and obliteration of the cavity of an interme- 

 diate i^art, and its conversion into the urachus, that gives 

 rise to the urinary bladder. The ultimate secreting tubuli 

 of both the Wolffian body and the kidney, are alike re- 

 markable for ending in dilatations which embrace con- 

 volixted capillaries — the so-called malpighian tufts. Neither 

 Wolffian bodies nor kidneys have been observed in Amphi- 

 oxus. It is doubtful whether true kidneys are developed 

 in Ichthyopsida, or whether the so-called kidneys of these 

 animals are not, rather, persistent Wolffian bodies. 



TJie 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 

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

 they are ripened into the peritoneal cavity, whence they 

 escape by abdominal pores, which place that cavity in direct 

 communication with the exterior. In many fishes, the 

 ovaries become tubular glands, provided with continuous 

 ducts, which open externally, above and behind the anus. 

 But, in all other Ve7-tebrata, 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 conveyed away by a special appa- 

 ratus, consisting of the Fallopian tubes, which resiilt from 



