THE FROG 103 



the ova find their way to the cloaca are the oviducts, or Miillerian 

 ducts. In adult females each of these ducts is a thick-walled, 

 twisted tube which lies in the abdominal cavity against the dorsal 

 body wall. Its anterior end opens into this cavity and is situated 

 at the side of the heart, while the posterior end opens into the 

 cloaca. The posterior portion of the oviduct is expanded and forms 

 the uterus, a reservoir for ova. 



The ova escape from the ovaries by the rupture of their walls 

 into the abdominal cavity ; they then make their way to the mouths 

 of the oviducts and through them into the cloaca. During this 

 descent of the ova the albumen which surrounds them is secreted 

 by the walls of the oviducts. 



At the anterior end of the kidneys is a pair of prominent, 

 yellow, branching fat bodies. They are lymphoid bodies and vary 

 much in size at different times of the year, being largest before 

 the breeding season and smallest after it. 



While studying the urogenital system, the organs of which it 

 is composed need not be disturbed. With a strong scalpel cut 

 through the bony pelvis exactly in the median line between the 

 legs in order to expose the cloaca. The urinary bladder is a deli- 

 cate structure which is attached to the body wall by mesenteries. 

 It must be freed from these, and great care must be taken not to 

 cut either it or the cloaca. 



Slit open the cloaca along the side and find the mouth of the 

 urinary bladder. Search with the blowpipe for the openings of the 

 urogenital ducts. 



Exercise 11, Make a semidiagrammatic drawing of the urogenital 

 system with the cloaca ; label carefully all its parts. 



The Nervous System. This system is made up of the following 

 divisions : ( 1 ) the central nervous system, which is composed of the 

 brain and the spinal cord ; (2) the peripheral nervous system, which 

 is composed of (a) the paired cranial and spinal nerves and (b) the 

 sympathetic nervous system; and (3) the special sense organs. 



The cranial nerves and the spinal nerves each number ten pairs ; 

 the former spring from the brain and the latter from the spinal 

 cord, placing these structures in communication with the various 



