54 'A BOOK OP WHALES 



ORGANS OF RESPIRATION 



Not only is the influence of a purely aquatic life to 

 be seen in the outward form of whales, the respiratory 

 organs and parts annexed show the same modification. 

 Bearing in mind the peculiar habits of whales, their 

 capacity for remaining a long time under water, and 

 the necessity therefore of supplying themselves with 

 a good stock of air for use during these prolonged 

 immersions, we should indeed expect to find that in 

 the vascular, as well as in the respiratory organs, there 

 were differences to be seen not found in mammals, 

 which are purely terrestrial. And this is precisely 

 what we do find. But here again it is not always 

 easy to distinguish between adaptational likeness and 

 real affinity ; it is, that is to say, not always clear 

 that structures supposed to be modified owing to the 

 habits of the creature are not marks of likeness to 

 some other family of mammals. But we shall con- 

 sider these points as they arise. 



Dr. Otto Muller, who has recently and elaborately 

 dealt with this matter,* has particularly dwelt upon 

 the form of the chest cavity in these aquatic mam- 

 mals. Among terrestrial creatures the shape of this 

 cavity is, as a rule, boat-like in transverse section. 

 The cavity narrows below and is wider above. 

 Furthermore, its ventral boundary line is about as 

 long as its dorsal ; the result of this being that the 



* " Untersuchungen uber die Veranderungen welche die Respirations 

 organe der Saiigethiere durch die Anpassung an das Leben im Wasser 

 erlitten haben." Jen. Zeitschr.f. Naturwiss., 1898, p. 93. 



