It is tempting to speculate on the reason for this peculiarity of structure. It may be 

 that the protection afforded by epithelium is unnecessary to animals living in a dust-free 

 environment. It is at least remarkable that the thin membrane of the capillary can be 

 subjected to the pressures involved in deep diving, which have been discussed (Laurie, 

 1933, passim) without the protection of a lining of epithelium to minimize the danger of 

 rupture. Again, it may be no more than coincidence that whales, which possibly alone 

 among mammals run no risk of oxygen deficiency in their blood (owing to the high 

 pressures at which the pulmonary gases are maintained during diving), should be with- 

 out epithelial cells which might be responsible for the secretion of oxygen which Haldane 

 and his co-workers found in man under conditions of oxygen shortage (Haldane and 

 Priestley, 1935, pp. 250-96). It is, however, by no means certain whether the epithelial 

 cells are responsible for the secretion of oxygen which these observers found. 



SUMMARY 



1 . Specimens of the lungs of four species of the larger Southern whales have been 

 sectioned and stained. 



2. Lungs of all the species examined agree in being massive in texture, in having a 

 thick, highly elastic pulmonary- pleura, and in being heavily invested with elastic tissue. 



3. Interalveolar septa are thick and composed largely of collagen with elastic fibres. 

 There is no alveolar epithelium, the air spaces being bounded by the endothelium of the 

 capillary network. This condition has not hitherto been found among land mammals. 



REFERENCES CITED 



Haldane, J. S., and Priestley, J. G., 1935. Respiration. Oxford. 

 Hartridge, H., 1936. Bainbridge and Menzies' Essentials of Physiology. London. 

 Laurie, Alec H., 1933. Some Aspects of Respiration in Blue and Fin Whales. Discovery Reports, vii, 

 PP- 363-406, pl- XV. 



