84 



On the Classification of Animals 



are metasthenic. Fleas, wliich are degradation al species, related 

 to Dipters, have the third or posterior pair of legs much the 

 longest and strongest. Among Macrural Crustaceans, the strongest 

 legs are, in the higher species, the first pair ; in others inferior, 

 the second ; in others still inferior (the Penaeids), the third pair. 

 Viewed on the ascending ^.^rade, this method is the preferent. 



3. Pervertive. — A subjection of an organ to any abnormal 

 function inferior to that normal to it ; as in the adaptation of 

 the nose of the Elephant to prehension ; of the antennse of many 

 inferior Crustaceans to prehension or h)comotion ; of the maxil- 

 lipeds of inferior Macrurans to locomotion ; of the forehead in 

 many Herbivores to purposes of defence. 



The perverted nose of the Proboscideans is one of the indica- 

 tions of their inferiority to the Carnivores ; but it is not neces- 

 sarily a mark of inferiority among Herbivores themselves, as the 

 faculty of prehension is one of those especially characterising Car- 

 nivores and other hischer Mammals, and nearly all Herbivores fail 

 of it. 



Viewed on the ascending grade, this method and the following 

 may be included under the term perfunctionative. 



4. Defunctionative.— Exhibited in the defectiveness or absence 

 of the normal function of an organ ; as in the absence of the 

 function of prehension from the fore-limbs of Herbivores (this 

 prehension in the fore-limbs belonging to the Mammalian type) ; 

 and that of locomotion mostly from all the limbs in the Muti- 

 lates ; that of locomotion from the female Bopyrus ; that of loco- 

 motion from Cirripeds and other attached animals ; that of the 

 sense connected with the second pair of antennse (and probably 

 also the first, these organs being obsolete) in the Lernseas and 

 Cirripeds, these antennse being simply prehensile organs in a 

 Lernsea, and constituting the base of the peduncle in an Anatifa.* 



This degradation and loss of functions is connected often with 

 the elliptic and amplificaiive methods of decephalization. It is 

 connected with the latter in the Bopyrus, and also in Cirripeds 

 and other attached species. 



C. Incremental. 



5. Ampl/ficative. — Exhibited in an elongation or general enlarge- 

 ment of the segments or members, and an increased laxness of the 

 parts. Includes the cases — 



a. Lengthening, widening, or laxness in the anterior portion of 

 the body ; the same in the posterior portion. 



* See " ExpL Exp. Eeport on Crustacea," p. 1393, and plate 96, where it is 

 shown that the antennee of the young Anatifa have a sucker-like organ for 

 attachment, and become, in the metamorphosis, the bottom of the peduncle by 

 which the adult Anatifa is attached* 



