

PEEFACE. 



On introducing this concluding volume to the reader, 

 I tender my sincere thanks to the Members of the 

 Council of the Ray Society for undertaking the 

 publication of my Monograph, and for the courtesy 

 which they have shown me in fulfilling my wishes as 

 to the form it should assume. 



Prof. Helmholtz well remarks that " The materials 

 of a monograph must be united by a logical process ; 

 and the first step is to connect like with like, and to 

 elaborate a general conception embracing them all." 

 Again, elsewhere, "A digest or catalogue may be 

 likened to a good lexicon ; with which almost a tyro of 

 the present day can achieve results in the interpretation 

 of the classics, which an Erasmus, with the erudition 

 of a lifetime, could hardly attain." 



Some may perchance think that this Monograph has 

 attained proportions unnecessarily large. The general 

 reader, on the one hand, may take exception to its 

 detail. The competent biologist, with more truth 

 perhaps, may complain of omissions as well as com- 

 missions. The first may call to remembrance and 

 apply the causticity of Montaigne when he says, " The 

 trade of the rhetorician is to make things appear and 



