198 



THE QUARTERLY REVIEW OF BIOLOGY 



optic chiasma, and this area is expanded 

 in contrast to the contracted zeuglodont 

 brain. The widening of this area is 

 correlated with elaborate visual capacities. 

 The brain casts of other extinct Miocene 

 porpoises show that the optic chiasmic 

 region was well developed, and there is 

 nothing to indicate that they differed 

 to any marked degree from their living 

 relatives so far as their visual powers are 

 concerned. 



As regards hydrostatic adjustments the 

 whale eye has been adapted to withstand 

 varying pressures as well as the impact 

 of the water when speeding at the surface. 

 It is a well known fact that a vault 

 designed to withstand heavy pressures has 

 to be built so that the directions of the 

 stresses, strains, and pressure forces fall 

 within the abutment. Putter (1901) 

 points out that the abutment in the whale 

 eye is the enormously thickened sclera. 

 Fluctuations in hydrostatic pressure result 

 in corresponding changes in intraocular 

 pressure. External pressure increases by 

 one atmosphere for each five fathoms of 

 depth. A blue whale (Sibbaldus musculus) 

 carried a line straight down for zzo 

 fathoms, where it would have to with- 

 stand a pressure of 45 atmospheres or 630 

 pounds per square inch, and it remained 

 below the surface for 3Z minutes. The 

 bottlenosed beaked whale (Hy-peroodon) 

 and the sperm whale (Physeter) are said 

 to descend half a mile and possibly a mile. 

 Pressures at such depths are enormous. 

 At half a mile the pressure is approxi- 

 mately 1 178 pounds per square inch and at 

 a depth of a mile about Z349 pounds per 

 square inch. 



The chemical adjustments of the whale 

 eye are equally interesting. Constant 

 chemical irritation resulting from contact 

 with sea water necessitates certain adjust- 

 ments to protect the eye from inflamma- 

 tion or even more serious injury. The tear 



gland does not secrete a watery liquid, 

 for the eye is no longer in danger of 

 drying up, but instead exudes a greasy 

 substance to protect the cornea from the 

 various chemical substances found in 

 sea water. No trace of the sebaceous 

 Meibomian glands has been found in the 

 eyelids of whales. Furthermore in a num- 

 ber of whales the conjunctiva or mucous 

 outside coating of the eye has been re- 

 placed by cornified epithelium. Since the 

 whale eye is subjected to almost constant 

 immersion in sea water of 3 to 4 per cent 

 salt content it does not appear unreason- 

 able to assume that these details represent 

 an adjustment to chemical irritants. 



Inasmuch as the cornea of the eye is in 

 direct contact with the water, one might 

 expect that the eye would be protected 

 in some way against continuous cooling 

 below normal body temperature, and curi- 

 ously enough the freezing point of the 

 liquid media in the whale eye (Sudzuki, 

 19x4) is somewhat lower (A 0.66 to 

 0.72. ) than in land mammals. The eye 

 also seems to be sufficiently protected 

 against variations in temperature by the 

 natural replacement of the liquid in the 

 anterior chamber, for inflow and drainage 

 are equal, and the aqueous humor should 

 be maintained at approximately the same 

 temperature as the blood. 



OLFACTORY SENSE 



Chemical senses, like those of smell and 

 taste, which are closely associated physio- 

 logically, require organs that differ con- 

 siderably in structure and relations. The 

 sense of smell plays an important part 

 in the welfare of many mammals, but 

 cetaceans apparently found less and less 

 need for olfactory structures. 



Stromer in 1908 described and figured 

 an unusually complete endocranial cast 

 (fig. zi) in situ in a zeuglodont skull 

 from the Qasr-el-Sagha beds of the Fayum, 



