CHAPTER XIX. 



CHORDATA (CONT.) : SUB-PHYLUM VERTEBRATA (FISHES, AM- 

 PHIBIANS, REPTILES, BIRDS, AND MAMMALS). 



LABORATORY EXERCISES. 



For general illustration of the vertebrates the author is 

 convinced that no form is superior to the frog for use in 

 elementary classes, although some teachers prefer a fish. In 

 a course arranged for one year it is not desirable to make 

 elaborate dissections of more than one vertebrate type. Direc- 

 tions are given both for the fish and the frog for the con- 

 venience of those teachers who prefer the former. Supple- 

 mentary studies for the other classes of vertebrates will be 

 found in connection with the chapters devoted thereto. 



333. Fish. Any common fish will serve perch, sucker, trout, smelt. 

 Specimens eight to ten inches in length are of most suitable size. Tf 

 convenient one half the class might take one species and the remainder 

 another. 



A. The Living Animal. Place in a tub of water, or better in a vessel 

 one side of which is glass. Watch the locomotion and notice all the ac- 

 companying motions of the various parts. What is the rate of the tail 

 stroke? How far, on an average, does one stroke of the tail carry the 

 fish? Compare these points when the fish is in very rapid motion. What 

 part do the anterior fins play in locomotion? Bind one of them flat against 

 the body with a string. Bind both. Results? Experiment similarly with 

 the other fins and see if your first conclusions are strengthened. Do you 

 find any variations in the above respects by comparing several species? 



How does the temperature of the fish compare with that of the water? 

 t Allow one specimen to remain for an hour or more in water at a tem- 

 perature of 70 F. ; another in cooler water (50 F.) : compare results. 



Can the fish detect in the water the presence of substances which have 

 a decided taste to us? Use colorless solutions, acid, sugar, quinine. Can 

 you get the animal to show any choice as to food? 



Note the motions of mouth and eyes. Can the fish see any point with 

 both eyes at once? 



B. External Anatomy. (Make careful outline sketches showing all 

 points of structure.) 



