148 MAMMALIAN SEXUAL CHARACTERS 



more or less the whole soma, but showing itself 

 especially in some particular organ or structure. 

 But I know of no mutation occurring under observa- 

 tion which consisted, not in a change of structure or 

 function, but merely in a change of position of an 

 organ from one part of the body to another, and 

 moreover a change which takes place by a con- 

 tinuous process in the course of development. If 

 the testes were developed from the beginning in a 

 different part of the abdomen, there might be some 

 reason in calHng the change a mutation. Moreover, 

 if it is a mutation, why has it never occurred in any 

 other class of Vertebrates except Mammals ? 



In 1903 Dr. W. Woodland published i a 

 Lamarckian theory of this mammalian feature, the 

 probability of which it seems to me has been increased 

 rather than decreased by the progress of research 

 concerning heredity and evolution since that date. 

 Dr. Woodland correlated the dislocation of the testes 

 with the special mechanical features of the mode of 

 locomotion in Mammalia. His words are : ' The 

 theory here advocated is to the effect that the 

 descent of the testes in the Mammalia has been pro- 

 duced by the action of mechanical strains causing 

 rupture of the mesorchial attachments, such strains 

 being due to the inertia of the organs reacting to the 

 impulsiveness involved in the activity of the animals 

 composing the group.' The ' impulsiveness ' is the 

 galloping or leaping movement which is characteristic 

 of most Mammals when moving at their utmost 

 speed, as seen, for example, in horses, deer, antelopes, 

 dogs, wolves, and other Ungulata and Carnivora. 

 It is obvious that when the body is descending to 



1 Proc. Zool. Soc.y 1903, Part i. 



