No. 39.— 1889.] ZOOLOGICAL TABLES. 



29' 



On the Formulae to be adopted, and their 

 Meaning. 



No sooner is an attempt made to classify a series of natural 

 objects than two great difficulties are encountered : the 

 subtlety of nature and the difference of opinion amongst 

 different observers as to the degrees of likeness and unlikeness 

 between different species or groups of species. The first is 

 well expressed by Cuvier. Speaking of his division Denti- 

 rostres in the Passerine birds, he says : — " The genera are 

 distinguished by the general form of the bill, strong and 

 compressed in the shrikes and in the thrushes, depressed in 

 the fly-catchers, fine and pointed in the warblers ; but the 

 passage from one to another is so graduated that it is difficult 

 to fix the limits of the genera." 



Here we have an attempt to classify bills only, and he 

 divides them into four types : the Shrike, the Thrush, the 

 Fly-catcher, and the Warbler type, but finds gradations 

 between them all. And it is almost always the same with 

 every part in every group of the animal kingdom, the diffi- 

 culty increasing with the length of the series chosen. This 

 was well understood by Linnaeus, and expressed in his cele- 

 brated maxim.* 



This difficulty might be lessened if naturalists could be 

 brought to agree as to degrees of likeness and unlikeness 

 between different forms : but birds have been united into 

 one and divided into thirty -two orders. The classification 

 of every part, and of the whole animal kingdom, is inces- 

 santly changing according to the views of different great 

 authorities, and the new lights thrown on the subject by 

 fresh discoveries in every department of Zoology. Nor is the 

 individual mind free from this difficulty. The bill that 

 appears to the student on one day to be most like the 

 thrush's he will be more inclined to class with the fly-catcher 

 series on another, and even with the shrikes on a third, and 



* " Natura non facit saltum." 



