HORNLESS CATTLE AND OTTER-SHEEP. 21 5 



a stable door the tail of a bull was wrenched off, and the 

 calves begotten by this bull were all born without a tail. 

 This is certainly an exception ; but it is very important to 

 note the fact, that under certain unknown conditions such 

 violent changes are transmitted in the same manner as 

 many diseases. 



In very many cases the change which is transmitted and 

 preserved by adapted transmission is constitutional or in- 

 born, as in the case of albinism mentioned before. The 

 change then depends upon that form of adaptation which 

 we call the indirect or potential. A very striking instance 

 is furnished by the hornless cattle of Paraguay, in South 

 America. A special race of oxen is there bred which is 

 entirely without horns. It is descended from a single bull, 

 which was born in 1770 of an ordinary pair of parents, and 

 the absence of horns was the result of some unknown cause. 

 All the descendants of this bull produced with a homed cow 

 were entirely without horns. This quality was found 

 advantageous, and by propagating the hornless cattle among 

 one another, a hornless race was obtained, which at present 

 has almost entirely supplanted the horned cattle in Paraguay. 

 The case of the otter-sheep of North America forms a similar 

 example. In the year 1791 a farmer, by name Seth Wright, 

 lived in Massachusetts, in North America ; in his normally 

 formed flock of sheep a lamb was suddenly born with a sur- 

 prisingly long body and very short and crooked legs. It 

 was therefore unable to take any great leaps, and especially 

 unable to leap across a hedge into a neighbour's garden 

 — a quality which seemed advantageous to the owner, as the 

 territories were divided by hedges. It therefore occurred to 

 him to transmit this quality to other sheep, and by crossing 



