THE DARWINIAN THEORY 41 



and in these so-called lop-eared rabbits the ear-muscles are partly 

 degenerated, and as a consequence of this lack of muscular strain the 

 skull has assumed another form. Thus the variation of one part may 

 influence the development of a second and a third organ, and may 

 even not stop there, for very often the influence has penetrated much 

 deeper and affected quite remote parts of the body. 



If any one were to succeed in adding a heavy pair of horns to 

 a breed of hornless sheep, there would run parallel with the course of 

 this variation, which was directly aimed at, a long series of secon- 

 dary changes which would affect at least the whole of the anterior half 

 of the body ; the skull would become thicker and stronger to support 

 the weight of the heavy horns; the neck-tendon {lig amentum nuchcu) 

 would have to become thicker to hold up the heavy head, and so also 

 with the muscles of the neck ; the spinous processes of the cervical 

 and dorsal vertebrae would become longer and stronger, and the fore- 

 legs, too, would need to adapt themselves to the heavier burden. 

 Every organism thus resembles, as it were, a mosaic, out of which no 

 individual group of pieces can be taken and replaced by another 

 without in some measure disturbing the correlation and harmony of 

 the whole : in order to restore this, the pieces all round about the 

 changed part must be moved or replaced by others. 



According to Darwin, it is to this correlation of parts that we must 

 refer the variation of other parts besides the one intentionally altered in 

 the course of breeding. It must be admitted that the mutual dependence 

 of the parts plays a very important role in the economy and develop- 

 ment of the animal body, as we shall see later, and these connexions 

 still remain very mysterious to us. Especially is this the case with 

 the connexion between the reproductive organs and the so-called 

 secondary sexual chai-acters. Removal of the reproductive organs 

 or gonads induces, in Man, for instance, if it be effected in youth, 

 the persistence of the childish voice and the non-development of the 

 -beard; in the stag the antlers do not appear, and in the cock the 

 comb does not develop perfectly, &"C., but we are not yet able to 

 understand clearly why this should be so. 



