DEVELOPMENT OF THE URINARY ORGANS. 973 



vertebrae, forming proportionally very large reddish masses, and reach- 

 ing from opposite the heart to the lower end of the vertebral column. 

 Originally, they consist of two symmetrical longitudinal canals, in the 

 walls of which slight csecal depressions speedily form. When fully 

 developed, they consist of numerous comb-like, blind, hollow processes, 

 lined with ciliated epithelium, very vascular, and communicating each 

 with a long duct, which runs downwards, and opens into the genito- 

 urinary sinus. Malpighian bodies, or arterial tufts, have been de- 

 tected in them. These organs are the Wolffian bodies, or primordial 

 kidneys, so called because their secretion contains, amongst other pro- 

 ducts, uric acid ; in Fishes, they are said to become the future kid- 

 neys. In the Warm-blooded Vertebrata, they are in no way connected 

 with the development of the kidneys, but rather with the first forma- 

 tion of the reproductive organs. Their secretion finds its way through 

 the genito-urinary sinus, into the allantois, or future urinary bladder. 

 They are proportionally larger in the lower Vertebrata, and persist 

 for a longer time. At first highly vascular, they afterwards almost 

 entirely disappear, as the proper kidneys are formed. The kidneys 

 themselves commence as thick, smooth, or lobulated opaque masses, 

 or processes of cells, arising from the sides of the cloaca, behind the 

 Wolffian bodies ; as these latter diminish, the kidneys enlarge, and 

 gradually receding from the urogenital sinus and cloaca, assume their 

 future normal position. They continue to be connected with the uro- 

 genital sinus, by a duct which forms the future ureter, pelvis, and 

 calyces. The renal matrix at first contains bundles of solid processes, 

 which afterwards become hollowed out, to form the tubuli uriniferi; 

 these are said not to open originally into the pelvis of the kidney. 

 The kidneys soon become lobulated, but afterwards smooth. Mal- 

 pighian bodies appear in them very early. The suprarenal bodies 

 are independent formations. 



On the inner side, and somewhat behind each Wolffian body, appears, 

 rather early, a little opaque mass, which is ultimately changed, ac- 

 cording to the sex, into the ovary or the spermatic gland. Two ducts, 

 the ducts of Miiller, appear simultaneously, connected at their lower 

 ends with the sinus urogenitalis, but terminating at their upper ends, 

 at first, in blind extremities. In the male, these become connected 

 with the spermatic gland, at the back of which, even in the adult con- 

 dition, they sometimes present a long diverticulum. In this situation, 

 too, vestiges of the Wolffian bodies may still be traced. (Giraldes). In 

 the female, these ducts do not coalesce with the ovaries, but remain 

 separate and form the oviducts of Fishes, Amphibia, Reptiles, and Birds, 

 the left one only usually persisting in the adult condition, in the two 

 last-named Classes. In the Mammalia, they constitute the free part of 

 the Fallopian tube ; between it and the ovary, are found, in the adult, 

 vestiges of the Wolffian bodies. (Rosenrnuller.) From the lower end 

 of these tubes, and from the portion of the genito-urinary sinus into 

 which these ducts open, the future uterus, or the prostate gland, is de- 

 veloped. In the Monotremata, an intermediate condition exists, ap- 

 proaching to the bird-like structure of the parts ; for the two Fallo- 

 pian tubes open separately into the urogenital sinus. In the Marsu- 



