370 



AQUATIC VERTEBRATES 



botton where a bather may step on it and receive a rather ugly wound 

 by the sharp, barbed spine, but it does not inject poison and, therefore, 

 is not in the nature of a sting. The electric ray possesses organs in its 

 body that actually generate electricity and when disturbed can give a 

 powerful shock to any intruder on its privacy. The sawfish has an ex- 

 tension from the front end of the head armed with sharp spines on either 

 side that make it resemble a saw. A sweeping side stroke of this saw 

 could repel any enemies that might be rash enough to disturb this 

 animal. 



Photo by Winchester 



Fig. 25.3. The sting ray. Note the long tail which bears the spine that gives this 

 ray its name. This specimen is resting on the bottom of the Marineland aquarium 



along with several sharks. 



Bony Fishes — Class Osteichthyes 



The word "fish" is rather loosely applied to almost any kind of animal 

 that lives in the water, but, strictly speaking, it applies only to members 

 of this class. An external examination seems to indicate that there is 

 only one pair of gill slits, but it appears this way because there is an 

 operculum, or gill cover, that covers the real gill slits which lie under- 

 neath. Upon raising the operculum it will be seen that there are actu- 

 ally four pairs of gills with five pairs of gill slits. There is a lateral line 

 as in the sharks. The bodies of most fish are covered by scales which 

 overlap like shingles on a roof. A close examination of these reveals 

 that they bear concentric rings of growth similar to those found on the 

 shell of a clam. The pelvic fins of the fish have moved anteriorly to 

 occupy a position near the center of the body or, in some forms, just 



