218 Animal Life and Intelligence. 



resemblance to an inorganic object or to another organism, 

 the variations of the several parts must be very closely, 

 and sometimes completely, correlated. The correlations, 

 however, need not, perhaps, have been simultaneous — the 

 resemblance having been gradually perfected by the filling 

 in of additional touches, first one here, then another there, 

 and so on. 



Concerning " organic variations," little need be said. 

 It is clear that an organ or limb may vary in size, such 

 variation carrying with it a correlative variation in power ; 

 or it may vary in complexity — the teeth of the horse tribe, 

 for example, having increased in complexity, while their 

 limbs have been rendered less complex ; or it may vary 

 in efficiency through the more perfect correlation and co- 

 ordination of its parts. 



The evidence of such variations from actual observation 

 is far less in amount than that of superficial variations. 

 And this is not to be wondered at, since in many cases 

 it can only be obtained by careful anatomical investigation. 

 Nevertheless, anatomists, both human and comparative, 

 are agreed that such variations do occur. And no one can 

 examine such a collection as that of the Eoyal College of 

 Surgeons without acknowledging the fact. 



Thirdly, " reproductive and developmental variations " 

 are of very great importance. The following are among 

 the more important modifications which may occur in the 

 animal kingdom. 



1. Variations in the mode of reproduction, sexual or 

 asexual. 



2. Variations in the mode of fertilization. 



3. Variations in the number of fertilized ova produced. 



4. Variations in the amount of food-yolk and in the 

 way in which it is supplied. 



o. Variations in the time occupied in development. 



6. Variations in the time at which reproduction com- 

 mences. 



7. Variations in the duration and amount of parental 

 protection and fosterage. 



