The Urinogbnitai, System. 



47 



lining of the coelom and discharging their products into the cavity, while 

 the kidneys are primarily tubular structures communicating also with 

 this cavity, so that they become modified in part as reproductive ducts. 

 The coelomic connections of the kidney tubules are with few exceptions 

 only seen in the embryonic condition, since the definitive kidneys in all 

 vertebrates are structures in which the tubules are connected with the 

 vascular system, and have either lost, or, as in the specialized permanent 

 kidneys of the mammalia, have not developed, the coelomic apertures. 

 The embryonic development of a mammal includes the formation 

 not only of a final kidney or metanephros, but also of two embryonic 

 structures, one of which, the first kidney or pronephros, is embryonic in 

 all vertebrates, while the second, designated as the mesonephros, or 

 embryonic kidney, is one occurring in the adult condition of intermediate 



Fig. 25. Diagrams of the male (A) and female (B) urinogenital 

 systems of the rabbit: b., urinary bladder; k., kidney; ur., 

 ureter; r, rectum. 



(A) — c.p., crus penis; d.d., ductus deferens; ep., epididymis; 

 g., gubernaculum; t., testis; v.s., seminal vesicle; u. v., male urethra. 



(B) — c.c, crus clitoridis; o., ovary; t.u., uterine tube; u.m., 

 female urethra; ut., uterus; va., vagina; vs., veslibulum. 



forms. It is from the ducts of the primary kidneys that the reproductive 

 ducts arise. Thus, in the female of most vertebrates the oviduct opens 

 by an expanded funnel into the coelomic cavity, usually at some distance 

 from the ovary; and, although in the rabbit the structure is said to arise 

 as a secondary development, it exhibits here as in other mammals the 

 feature of a coelomic opening, coupled with that of close association with 



