LABORATORY WORK: FISH. 



For this purpose any common fish perch, sucker, pout, 

 etc. from ten to twelve inches in length will answer. If 

 time permit, it will prove very advantageous to take two 

 different fishes and work out the following points, compar- 

 ing their resemblances and differences. 



I. EXTERNAL CHARACTERISTICS. 



TOPOGRAPHY OF BODY. Distinguish in the fish anterior 

 and posterior, a back (dorsum) and a belly (venter), and 

 right and left sides. Make out the regions : head, trunk, 

 and tail. Is there a neck ? Where is the mouth ? the 

 vent ? 



How many fins can you find ? How many are in pairs ? 

 How many single ? Are any in the median line of the 

 body ? Is there a skeleton to the fins ? Could you regard 

 a fin as a fold of the skin supported on soft or spiny 

 rays? 



Of the median fins the caudal terminates the tail, the 

 dorsal is on the back, the anal is just behind the vent. 

 Are there two of any of these ? Are the upper and lower 

 lobes of the caudal equal (homocercal) or unequal (hetero- 

 cercal). 



Can the paired fins be compared in position to your 

 own limbs? By feeling, ascertain if there be any solid 

 support in the body for either pair. How does this con- 

 dition compare with that in man ? The anterior paired 



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