190 



ANIMAL BIOLOGY 



find their way to the exterior by a pair of minute abdominal 

 pores. In higher forms, however, special sperm ducts and ovi- 

 ducts are developed in close relationship with the urinary system. 

 (Fig. 132.) 



In some aquatic, and most terrestrial Vertebrates, fertilization 

 occurs while the eggs are still within the oviducts; the copulatory 

 organ transferring the sperm directly to the terminal portion of 



Opening of oviduct into coelom 

 Dorsal aorta 

 Posterior vena cava 



Fat body 



Testis 



Oviduct 

 Adrenal bodies 



Kidneys 



Mesonephric ducts 

 or ureters 



Uterine dilation of oviduct 

 Vestigial oviduct in male 



Openings of ureters 



MALE 



Cloaca 



Opening of 



oviduct into 



cloaca 



FEMALE 



Fig. 132. — Urogenital organs of the Frog. 



the ducts through which they make their way up to meet the de- 

 scending eggs. After fertilization the zygote may soon pass to the 

 exterior; usually, as in the case of the familiar hen's egg, after 

 being wrapped up in nutritive and protective coats secreted about 

 it during its passage down the oviduct. Or, as is the case rarely 

 among lower forms and the rule among all Mammals except the 

 Monotremes, the zygote on reaching the lower part of the oviduct 

 becomes attached to the wall of an enlargement of the oviduct, 

 or of a chamber formed by the union of the two oviducts, called 



