802 THE EXCRETORY AND REPRODUCTIVE SYSTEMS 



b. Female Reproductive Duct 



In the eutherian or placental mammals, the two Mullerian ducts in most 

 species unite posteriorly to form a single uterovaginal complex (fig. 349B, 

 D). In all other vertebrates, the Mullerian ducts or oviducts remain sep- 

 arate (see figures 33; 351A-4, B-4). The vagina of the eutherian female 

 mammal probably is constructed partly of entoderm from urogenital sinus, 

 for entoderm from this area invades the caudal end of the uterovaginal rudi- 

 ment and lines the vaginal wall, at least in part (fig. 349B, D). 



In the teleost fishes (fig. 35 IM, N), the origin of the MUllerian ducts is 

 problematical (Goodrich, '30, pp. 701-705). 



5. Development of Intromittent Organs 



Various types of intromittent structures are described in Chapter 4. The 

 development of pelvic-fin modifications under the influence of the male sex 

 hormone occurs in fishes. Cloacal intromittent structures are developed in cer- 

 tain Amphibia. A definite penis occurs in reptiles, certain birds, and in all 

 mammals. The transformation, occurring in the external genital structures in 

 male and female human embryos, is shown in figure 349E-K. 



6. Accessory Reproductive Glands in Mammals 

 Refer to figures 2 and 349C. 



a. Prostate Gland 



The prostate gland arises as entodermal outgrowths from the membranous 

 urethra near the entrance of the genital ducts. The surrounding mesenchyme 

 provides the connective tissue and muscle. The paraurethral glands or ducts 

 of Skene in the female represent minute homologues of the prostate gland. 



b. Seminal Vesicles 



The seminal vesicles arise as saccular outgrowths from the mesonephric 

 ducts. 



c. Bulbourethral Glands 



The bulbourethral (Cowper's) glands in the male arise as outgrowths from 

 the entoderm of the cavernous urethra. The vestibular glands or glands of 

 Bartholin are the female homologues of the bulbourethral glands. 



7. Peritoneal Supports for the Reproductive Structures 

 a. Testis and Ovary 



The testis and ovary are pendent structures in all vertebrates and they are 

 supported by peritoneal extensions from the dorso-lateral region of the 



