SENSES AND THE CENTRAL NERVOUS SYSTEM 



237 



Figure 122. Skull of Archaeocete (Dorudon stromeri) with 

 brain and nasal cavities drawn in. L = lachrymal duct; 

 J\f = nasal cavity with distensions and projections ; B = 

 olfactory bulb; O = optic nerve; B = brain. {Kellogg, 

 1929-) 



its extremity, the so-called olfactory bulb which 

 is found in most vertebrates. It is not yet known 

 whether adult Mysticetes have a functioning 

 olfactory nasal epithelium, but the presence of 

 an olfactory nerve makes it likely. Embryos, 

 moreover, have been shown to have olfactory 

 receptors in their nasal epithelium. 



Archaeocetes, which lived forty million years 

 ago and which we have discussed at length in 

 Chapter 2, undoubtedly had a very much keener 

 sense of smell than their modern relatives. This 

 is inferred from the structure of their nasal 

 cavity, and particularly from the presence of 

 characteristic lamellae of bone which, in other 

 mammals, are covered by olfactory epithelium 

 (Fig. 122). In modern Odontocetes, on the other hand, all traces of an 

 olfactory organ or nerve are generally absent, though the ethmoid of 

 some of their Miocene ancestors was found to be perforated to admit the 

 olfactory nerve, so that fifteen million years ago these animals may well 

 have been able to smell. 



No discussion of the organ of smell \vould be complete without some 

 remark about Stenson's duct. Vestiges of this duct are found in all 

 Cetaceans, where they take the form of one or two small grooves inside the 

 tip of the upper jaw. These grooves are clearly visible even in adult whales, 

 though they seem to fulfil no function at all. Moreover, there are no traces 

 of the duct itself, let alone of a vomeronasal (Jacobson's) organ. 



The sense of taste will be discussed at greater length in Chapter 10, so 

 that we can conclude our survey of the Cetacean senses with a few remarks 

 on the sense of touch. We must pass over the perception of pain and heat 

 stimuli in silence, since very little is known on this subject. Papers on the 

 Cetacean spinal cord usually state that the Cetacean sense of touch and 

 particularly the sensitivity of the skin are poorly developed, but they are 

 surely wrong since, for instance, stranded dolphins have often been 

 observed to react to even the most gentle touch by movements of the body 

 or of the eyelids. Moreover, the Bottlenoses and also the Pilot Whales in 

 the Marineland aquarium love to be stroked by their keepers, and Bottle- 

 noses have been seen stroking each other with their pectoral fins during 



