THE FROG. 35 



spond to the conditions described for the male? Are there 

 ureters distinct from the oviducts? Draw the repro- 

 ductive and urinary organs of your specimen. 



Insert a blowpipe in the glottis (p. 33) and inflate the 

 lungs. What is their shape? Are they made up of little 

 chambers (air-cells) throughout? 



Between lungs and liver is the pericardial cavity, and 

 through its walls in the freshly killed specimen the beating 

 of the heart can be seen. Open the pericardium very care- 

 fully and expose the heart; make out the ventricle behind, 

 and the auricles in front. Arising from the ventricle and 

 crossing the auricles is the arterial trunk. Carefully clean 

 this from the surrounding tissues and trace it to its divi- 

 sion. Then follow each trunk. The right one soon di- 

 vides into three branches; the anterior is the carotid, the 

 middle the aortic arch, the third the pulmonary artery. 

 How does the trunk of the left side differ? 



Trace the carotid arch. Where does it go? What be- 

 comes of the aortic arch? Do you find a dorsal aorta? 

 On which side of the alimentary tract should the dorsal 



*/ 



aorta be (p. 19)? To what organs is the pulmonary artery 

 distributed? Do you find anything to compare with the 

 ventral aorta (p. IS) and afferent and efferent branchial 

 arteries? Draw the circulatory system as made out, viewed 

 from the ventral surface. 



Place a drop of blood of the frog on a slide, cover it 

 with a cover-glass, pressing it well down, and examine 

 under the higher power of a microscope. What is the 

 shape of the corpuscles? Are all alike in shape and size? 

 Stain with fuchsin (see Introduction) and study again. 

 Are all parts equally stained? 



Split the skin along the back and pull it away. Find the 

 point where the head joins the back-bone; and beginning 



