CHAPTER VIII 



CELLULAR STRUCTURE OF THE TOAD (OR 



FROG) 



LABORATORY EXERCISE 



The blood. TECHNICAL NOTE. The blood of a frog can be 

 studied as it flows through the small vessels in the membranes 

 between the toes while the animal is alive. Place a frog on a small 

 flat board which has had a hole cut near one end, and with a 

 piece of cloth bind it to the board. Spread the web between two 

 toes over the hole in the board and keep it in place with pins. 

 This done, examine the distended web under the compound micro- 

 scope first with low then with higher power, and observe the blood- 

 vessels and the blood circulating in them. For a further study of 

 the blood kill a toad or frog and place a drop of the blood on a 

 slide with a cover-glass over it. 



Put the prepared slide under the microscope and note 

 that the blood, which as seen with the unaided eye 

 appears to be a red fluid, is made up of a great many 

 yellowish elliptical disks or cells, the blood-corpuscles, 

 floating in a liquid, the blood-plasma. Here and there 

 you may notice amoeboid blood-corpuscles. These are 

 irregular-shaped cells which move about by thrusting out 

 pseudopodia. They look like some of the unicellular 

 animals, as the Amccba. Can you distinguish a nucleus 

 and cell-wall in the blood-cells ? 



Make drawings of these blood-cells. 



The skin. TECHNICAL NOTE. Keep a live toad or frog in 

 water for some time and note if its skin becomes loose or begins to 

 slip away. If the outer skin, epidermis, comes off, take some of the 

 shed skin and wash it in water, then stain for three or four minutes 

 in a solution of methyl-green and acetic acid (seep. 451). Cut 



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