INTRODUCTION. XXVU 



Now it is clear that from an investigation of all three 

 classes just mentioned, Ave shall be able to gain an 

 idea of those points which are common to all parts, to 

 all individuals or to all aggregates, and those that are 

 pecuhar to some of them, and, by eliminating the one 

 from the other, we shall arrive at conclusions which 

 will be more or less generally accurate or applicable, 

 according to the ability of the student and the extent 

 to which the comparative analysis is carried. It is thus 

 that morphologists have been enabled to frame types or 

 standards of reference, and systematists to collocate the 

 organisms they deal with into groups. These standards 

 and groups are more or less artificial (none can be 

 entirely natural) in proportion to the amount of know- 

 ledge possessed by their framers, and the use they 

 make of it. 



From this point of view teratological metamorphosis 

 of all three kinds demands as much attention as that 

 which is called normal. We can have no thorough 

 knowledge of an organ, of an individual which is an 

 aggregate of organs, or of an aggregate of individuals 

 of whatever degree, unless we know approximately, at 

 least, what are the limits of each. It is not possible 

 to trace these Hmits accurately in the case of natural 

 science, but the larger our knowledge and the wider 

 our generalisations, the closer will be our approach 

 to the truth. 



The most satisfactory classification of malformations 

 would be one founded upon the nature of the causes 

 inducing the several changes* Thus, in all organised 

 beings, there is a process of growth, mere increase in 

 bulk as it were, and a process of evolution or metamor- 



