AQUATIC MAMMALS 



7. Location of the bulbus away from the bony walls and embedded 

 in muscular, fatty and glandular tissue. 



8. Acquisition of a special hydrostatic sensory organ in the Odon- 

 toceti. 



Chemical adaptations 



1. Development of glands to produce a fatty, oily secretion. 



2. Increase in size of Harter's and lachrymal glands, and develop- 

 ment of a subconjunctival stratum of glands. 



Putter suggested that as the eyes are immovable, the very large re- 

 tractor muscles may have developed a specialized function and that it 

 is possible that they may now act to develop heat to warm the eye. 

 But there is apparently not the slightest basis for this theory. Even if 

 these muscles were continually contracted and relaxed the heat furnished 

 could hardly be a fraction of that supplied to the eye by the blood 

 through the retia mirabilia. Similarly with the structure in the eyes 

 of odontocetes which he interpreted as a hydrostatic organ. This was 

 a bit of neural epithelium in the connective tissue of the sclera at the 

 angle of the iris and isolated from the retina so that it could receive 

 no stimulus by means of light. I can see no reason for considering 

 this to have any hydrostatic function. 



In summarizing the aquatic specialization which the whale's eye has 

 undergone Kellogg (1928) has stated that "in its gross features the 

 whale eye differs from that of a land mammal in having an eyeball 

 immovable, eyelids without eyelashes, no tarsus or supporting cartilage 

 in the eyelid, no Meibomian glands, and a downward direction of the 

 eye axis. As the result of an aquatic mode of life whales have acquired 

 a more spherical lens and a greatly thickened sclera. The ciliary pro- 

 cesses and their muscles are reduced in size and have lost their original 

 function of controlling the shape of the lens. The tension of the 

 suspensory membrane (the zonula Zinii) is not great enough to flatten 

 the anterior surface of the lens, and as a general rule the latter retains 

 a more or less spherical shape. Whales thus lack the power of ac- 

 commodation." 



The more spherical lens projects the image upon a retina that is rela- 

 tively much nearer the lens than in the normal eye. This is accom- 

 panied by an enormously thickened sclera, and it is this which stands 

 the optic stress experienced during deep diving. 



The above lack of accommodation is not unique, for it is a character 

 shared by a number of land mammals. 



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