250 



WHALES 



Figure 12(). Top view of the brain of a 

 rabbit, a cow and a man, showing 

 differences in the development of the con- 

 volutions of the cerebral cortex. Note that 

 the cerebrum of the rabbit extends least, 

 and that oj man most, towards the rear. In man the cerebrum completely covers the cerebellum. 

 C = cerebellum; S = spinal cord. 



much less developed than it is in most other mammals, and the olfactory 

 sense may be completely absent. The influence of sight on the size of the 

 brain may be shown by the fact that, according to Anderson, the cerebrum 

 of the Gangetic Dolphin is not only much smaller, but has also a sig- 

 nificantly smaller number of convolutions than the cerebrum of other 

 Odontocetes (Fig. 130). On page 228 we saw that the eye and the optic 

 nerve of this animal are rudimentary. 



Some scientists prefer to ascribe the large Cetacean brain primarily to 

 strong muscle development and to the associated highly differentiated 

 nervous structure. Without further explanation, however, it seems 

 improbable that an animal which propels itself mainly with its tail should 

 need a more highly developed brain than, for instance, a monkey which 

 uses all its limbs so skilfully. 



Another important contribution to tlie solution of the problem of the 

 mammalian brain - which is still far from solved - was offered by Crile 

 and Quiring in 1940. From a careful investigation of the brains of 

 hundreds of different vertebrates, they gained the clear impression that an 

 animal's metabolism has important effects on the development of its brain 

 in general, and of the cerebrum in particular. The higher the metabolic 

 rate, the faster not only the heartbeat and the respiratory rate, but 



