232 



WHALES 



Figure 120. A Botllenose Dolphin in Marineland, Florida, jumping for fisli. 



sharply on the lower retina, and aquatic images on the upper retina. 

 However, the whole subject requires further investigation. 



Another factor affecting the eye of aquatic animals is water pressure. 

 While the eye, like all other Cetacean tissues, is constructed of extremely 

 incompressible material (see Chapter 4), water pressure may only alter its 

 shape. Now we have seen that the shape of the eye affects the sharpness 

 of the image and the width of the visual field, and since the Odontocete 

 eye, particularly, lacks much of the bony orbit protecting our own eyes, 

 it must have special safeguards against pressure distortion. 



Most whalers could tell you and possibly even show you ho^v the shape 

 of the Cetacean eye is maintained, since the eyes, like the 'ears', are often 

 taken home as trophies. The contents of the eye are pulled out through the 

 back, where an opening admits the optic nerve, an electric bulb is fitted 

 in, and light is made to shine through the cornea. While the cornea 

 geneially becomes dry and somewhat crinkly, the eyeball itself retains 

 its shape thanks to the enormous thickness of its tough sclera. And it is 

 this coat which guards the eye of living Cetaceans from undue distortion. 

 Its exceptionally hard connective tissue is many scores of times thicker in 

 Rorquals than it is in terrestrial mammals, and even porpoises and 

 dolphins have a particularly thick sclera (Fig. 118). 



While sea-water keeps the Cetacean eye permanently moist and clean, 

 the great masses of water which continuously stream past the cornea at 

 great speed naturally expose it to very much more wear and tear than a 



