CHAPTER II 



AMPHIBIANS 



A CAUDATE AMPHIBIAN. NECTURUS 



Necturus, or the mud puppy, is one of the largest of the sala- 

 manders. It is common throughout the central portions of the 

 country, where it lives in lakes and streams and feeds upon small 

 fishes and other animals. It is one of the most primitive am- 

 phibians. The external gills, which in most amphibians are larval 

 characters and disappear as the animal becomes adult, are retained 

 throughout life by Necturus ; it never leaves the water. 



Three specimens will be needed for a complete dissection : one 

 for the study of the external characters and the viscera, including 

 the heart and the principal blood vessels ; one for the dissection of 

 the entire vascular system ; and one for the skeleton. They should 

 be preserved in a 5 per cent solution of formalin or in cold storage. 



Place the animal, alive if possible, on a dissecting board or in 

 a large pan and observe its form and color. The body is cylin- 

 drical in shape, flattened dorsoventrally except at the hinder end, 

 which is compressed laterally and surrounded by a dorsoventral 

 fin. The tail is the principal organ of locomotion. The small, weak 

 legs, with the clawless toes, are of use only when the animal walks ; 

 while it is swimming they are held against the sides of the body. 



The skin of Necturus is smooth, as in most amphibians, and 

 without bony or horny scales or other hardened integumentary 

 structures such as are possessed by all the other groups of verte- 

 brates. It is, however, provided with numerous integumentary 

 glands, which secrete a protective but nonpoisonous slime. Along 

 the middle of the back a double row of these glands will be seen 

 when the skin is removed. 



Note the color of the animal, and the variation of color on the 

 dorsal and ventral sides. The animal is well fitted by its color 

 for a life in the dimly lighted waters in which it is found. 



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