490 THE CAT. [CHAP. xm. 



specialization of structure is presented by Machcerodus and Ensmilus, 

 and that Cyncehirus is the most exceptional form amongst living 

 felines, and one in which some of the distinctive characters of its 

 family (e.g., the retractility of the claws), are poorly developed. 

 The cat's genus, Felis, is one which, while it well exemplifies the 

 characters of the family to which it belongs, yet does not exhibit 

 any of those characters developed either in an extreme or in an 

 aberrant manner. This statement needs some explanation. Every 

 group of animals containing various species consists of certain kinds, 

 which are more or less alike, and differ but little from an ideal 

 standard which is the type of such group. Such kinds are 

 normal forms. Besides these, there are generally certain other 

 kinds which are peculiarly modified in one way or another, depart- 

 ing more or less widely from the normal structure. Such divergent 

 kinds are said to be aberrant or abnormal. Also both " normal " 

 and "aberrant" forms may be either what is called specialized or 

 generalized. "Specialized" creatures are such as have an ex- 

 ceptional organization of a definite kind. " Generalized " creatures 

 are such as resemble the general run of animals to which they are 

 more or less closely related, but have the distinctive characters of 

 their group poorly developed. But besides the specialized and 

 generalized normal forms, there may be other normal forms which 

 are neither of these, but adhere closely to the type and express it in 

 its intensity, yet without any one-sided development of it. These 

 are TYPICAL FORMS. The full meaning of these terms can only be 

 made clear by examples, for which it is necessary to refer to some 

 other group of animals with which the reader may be acquainted, 

 or with which he can easily become so. Let us then take, as examples, 

 species of the well-defined group of ruminating beasts. Amongst 

 them we have creatures which adhere to the normal structure, but 

 yet its characteristic features are in them but poorly developed. 

 They are then generalized normal forms, as, e.g., that small South 

 American deer, the yenadaor pudu (Pudu humilis). Others, which 

 adhere to the normal structure, may carry it to an intense but some- 

 what one-sided degree of development. Such would be specialized 

 normal forms, as, e.g., the elk or the four-horned antelope. Others 

 again may diverge from the general type in the direction of other 

 creatures outside their group. Such would be generalized aberrant 

 forms, such as the camel and llama, or as the chevrotains ; whilst 

 others may diverge from such type in a special direction of their 

 own, and such would be called specialized aberrant forms, as, e.g., 

 the giraffe. 



Finally, others will be normal, and yet with the characters special 

 to the group strongly developed, i.e., they will be typical forms, as, 

 e.g., the red deer or the Indian antelope. 



To apply these remarks to the Felidce, we have an example of 

 a " generalized normal form " in the cheetah, Cyncclurus. The lion 

 is an example of a " specialized normal form." For a " generalized 

 aberrant form " we must have recourse to fossils, such as Dinictis, 



