ITS NEABEST EXISTING RELATIONS 



65 



active, and their position is such that when the animal is 

 feeding particles of the odorous secretions will fall on 

 and adhere to the herbage around, and thus afford in- 

 dications to any other animals of the same species that 

 may for some time afterwards pass over the same ground. 



The presence of this gland in the hipparion and its 

 absence in the more modern Equidce has been given 

 as a reason for supposing that the latter are not the 

 direct descendants of the former, but must have been 

 derived from some other form in which such a specialisa- 

 tion had not been developed. This, of course, is proba- 

 ble ; but it must not be forgotten that very slight changes 

 in habits, or the increased power and use of other senses 

 than that of smell, may have diminished the value of the 

 information afforded by means of this gland, and ulti- 

 mately led to the elimination of the organ itself. It 

 may be that a change from a life habitually passed in 

 forests or scrub to one in open plains would be sufficient 

 to account for such a modification in structure. In any 

 case, it is one which must be very easily brought 

 about, without any other great changes, as the modern 

 ruminants show, being present or absent in them quite 

 irrespectively of real affinity, as indicated by more funda- 

 mental and less superficial and adaptive structural 

 characters. It would be interesting to make a careful 

 microscopical examination of the skin of this region in 

 all existing species of Equidce, to ascertain whether any 



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