THE STUDY OF AN AMMAL TYI'K 



Can both eyes focus together upon the same object (binocular 

 vision) or each eye separately (monocular vision) ? Why? Ask 

 the instructor for a method of detcrinininp; your own angle 

 of vision. Represent by a simple (iiagrain. Looking clown 

 upon the top of the frog's head determine the angle of vision 

 of each eye. Represent by a diagram. What do you judge to 

 he the relative merits of the two kinds of vision? 



On the side of the head caudad of the eye is a flat disk, the tym- 

 panum or eardrum, which responds to vibrations impinging 

 upon it. By careful manipulation determine tlie nature and 

 attachments of this membrane. Near the center on the inner 

 surface of this membrane there is attached a small rod, the 

 columella, which transmits the vibrations of the tympanic mem- 

 brane to the inner ear or receptive organ of the sense of hearing. 

 Carefully remove the cephalic third of the membrane as an aid 

 in discovering its inner relation.s. If difficulties are encountered 

 ask the instructor for assistance. 



In the mesal line of the head, slightly cephalad of the level of 

 the eyes, there is a small light-colored spot termed the brown 

 spot. Its significance will be mentioned later. For the present 

 locate it only. 



The anus (the caudal opening of the intestine) appears to be 

 located on the dorsal side rather than at the exact caudal end or 

 on the ventral side. 



A survey of the sense organs (receptors) reveals them as organs 

 located at the surface or in direct communication with the sur- 

 face. Bearing in mind the general service of the sense organs 

 what is the fitness of their location? 



Letting a horizontal line represent the frog's body, locate, by 

 means of numbers or symbols, the organs of the five special 

 senses (vision, smell, hearing, taste, and touch). What is the 

 result? Of what obvious advantage to the animal? 



Identify the dermal plica: or thickened folds of skin extending 

 caudad from the posterior angle of the eyes. Those folds lodge 

 important skin glands. 



Make a drawing of the dorsal aspect of the frog, life size fif 

 the frog 1)0 of modium size), representing the features mentioned 

 in this study. 



