I.] THE FROG. 41 



toneal cavity; a similar fluid will be found to be 

 present, but to a lesser degree, imparting a moist- 

 ness to the organs therein contained. 



C. The study of transverse sections. Especially with a 

 view to ascertaining the limits and mutual relationships 

 of the larger cavities and the body-wall, together with 

 the mode of suspension of the viscera. 



Obtain a frog (preferably one which has been for 

 24 hours or longer in spirit) and make transverse 

 sections across its body, as directed below. Examine 

 under water. 



I. Across the mid region of the trunk; to pass through 

 the kidneys,' genital glands, and large intestine. 



a. The body-wall ; especially its muscular constituent, 

 which is thickened dorsally in the region of the 

 back. 



I). The splanchnic {pleiiro-peritoneal) cavity ; ventral 

 and spacious ; it lodges the organs of the viscera, 



c. The neural cavity; relatively small, situated in the 

 dorsal middle line and enclosed on all sides by 

 the bony vertebral column. It lodges the central 

 nervous system, seen, in section, as a delicate white 

 cord. 



d. The alimentary canal; cut across at various points. 

 Remove those portions of it which do not happen 

 to be connected by mesentery with the body-wall 

 or other parts. The large intestine will be seen in 

 section in the ventral middle line ; take note of its 

 position and relationships. 



e. The kidneys ; lying close together, dorsally to all 

 the other organs and obliquely disposed. 



