12 THE MODERN STUDY OF ZOOLOGY 



of Malpighi, Swammerdam, and their successors 

 gradually revealed the details of minute structure 

 and rendered possible a correct appreciation of the 

 anatomy of animals previously too small to be 

 investigated, it was gradually realised that the 

 Linnaean system, with its hard and fast lines of 

 division, no longer represented the actual state of 

 our knowledge, and classification by definition 

 gradually gave way to the second form of morpho- 

 logical classification classification by type. 



We may explain the difference between the two 

 by means of our former illustrations : thus, to take 

 our first case, we no longer divide our paper by 

 artificial lines, we now look to the dots themselves ; 

 we find that the dots are not always the same 

 distance apart, that many of them fall naturally 

 into groups of various sizes ; each well-marked 

 group we give a name to, and the central member 

 of the group round which the others seem to be 

 arranged we call the type of the group : of the 

 remaining dots, some are so close to our big groups 

 that we include them with these, others form 

 distinct smaller groups of their own, whilst some 

 solitary ones stand quite apart and isolated from all 

 the rest. Or we may, to take our second instance, 

 illustrate classification by type by a map of 

 England, in which the county boundaries are left 

 out, but all the towns and villages marked. Here 

 we have large centres such as London or 

 Manchester, containing large numbers of inhabi- 

 tants, and representing distinct types ; smaller 

 centres lying immediately round them, not definitely 



