CLASSIFICATION. 31 



linear series, every member of the series being higher in point 

 of organisation than the one below it. As we have seen, how- 

 ever, the status of any given animal depends upon two condi- 

 tions 1 one its morphological type, the other the degree to 

 which specialisation of function is carried. Now, if we take 

 two animals, one of which belongs to a lower morphological 

 type than the other, no degree of specialisation of function, 

 however great, will place the former above the latter, as far 

 as its type of structure is concerned, though it may make the 

 former a more highly organised animal. Every Vertebrate 

 animal, for example, belongs to a higher morphological type 

 than every Mollusc ; but the higher Molluscs, such as cuttle- 

 fishes, are much more highly organised, as far as their type is 

 concerned, than are the lowest Vertebrata. In a linear classi- 

 fication, therefore, the cuttle-fishes should be placed above the 

 lowest fishes such as the lancelet in spite of the fact that 

 the type upon which the latter are constructed is by far the 

 higher of the two. 



It is obvious, therefore, that a linear classification is not 

 possible, since the higher members of each sub-kingdom are 

 more highly organised than the lower forms of the next sub- 

 kingdom in the series, at the same time that they are con- 

 structed upon a lower morphological type. 



In the words of Professor Allen Thomson, "It has become 

 more and more apparent in the progress of morphological 

 research, that the different groups form circles which touch 

 one another at certain points of greatest resemblance, rather 

 than one continuous line, or even a number of lines which 

 partially pass each other." In the same way the highest 

 vegetables do not approximate to, or graduate into, the lowest 

 animals ; but " each kingdom presents, as it were, a radiating 

 expansion into groups for itself, so that the relations of the 

 two kingdoms might be represented by the divergence of lines 

 spreading in two different directions from a common point." 



BINOMIAL NOMENCLATURE. Since the time of Linnseus it has been 

 the practice of naturalists to designate all species by double designations, the 

 first part of the title indicating the genus to which the animal belongs, 

 whilst the second is the proper or specific title. Thus the Dog is known 

 by the "binomial" designation of Cams familiaris. The "genus" Cants 

 contains other species besides the Dog such as the Wolf and Jackal 

 but the i&xs\& familiaris indicates that this title belongs to the Dog and not 

 to either of the latter. The genus Cam's, again, belongs to the "family" 

 Canidce, including other genera, such as the Foxes ( Vulpes). The family 

 Canidce, further, is one of a number of families, such as the Cats (Felida), 

 the Bears (Ursidce}, the Hyaenas (Hycznidtz), &c., which collectively con- 

 stitute the ' ' order " of the Carnivora or Beasts of Prey. The Carnivora, 



