CHAPTER IX 

 BRANCH CHORDATA: THE VERTEBRATES 



THE PERCH 



EXTERNAL ANATOMY 



I. — General Form. Study the graceful outline of the fish 

 from a side view. From a dorsal view, see how the 

 body is compressed laterally. Observe how the head, 

 although flattened at the tip, passes with graceful 

 curves into the body. Account for the compressed 

 body, flattened head, and the absence of a neck by refer- 

 ence to the animal's habitat and locomotion. Notice 

 the absence of any segmented division of the body axis. 

 Segmented structures will be found to exist, however, 

 when we study the skeleton and muscles. Study the 

 coloration of the fish. Account for its dark dorsal and 

 light ventral surface by reference to its needs of self- 

 protection. Notice the alternating perpendicular bands 

 of black and white along the sides. Explain how this 

 arrangement of color also makes the fish less conspicu- 

 ous in its natural haunts. 



II. — Exoskeleton. Study the scales of the perch. Re- 

 move some of them, and with the low power of the 

 microscope see the thin covering. Draw one. The 

 scales themselves are the outgrowths of the inner or 

 true skin, while their covering corresponds to the outer 

 skin or epidermis of the higher animals. 



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