based on the Frinciple of Cephalimtion. 



83 



group — the fixed point for reference — holds a position towards 

 the top of the group. The methods, as given, are therefore more 

 strictly methods of decephalizatlon than of cephalization ; but the 

 former are simply tlie reverse of the latter. 



A. Size (or force) of life-system. 



1. Potential. — Exhibited in less and less force and size of life- 

 system with decline of grade (and the reverse, with rise of grade) ; 

 as that in passing from the type of Megasthenes (Quadrumanes, 

 Carnivores, Herbivores, and Mutilates) to that of Microsthenes 

 (Chiropters, Insectivores, Rodents, and Edentates) ; or from that 

 of Decapods to that of Tetradecapods among Crustaceans — in 

 which latter case, unlike the former, there is also retroferent de- 

 cephalization ; and so, generally, in passing from a higher to a 

 lower type, it being equivalent to passing to a type of smaller and 

 weaker life-system. 



B. Functional. 



2. Retroferent. — A transfer of functions backward that belong 

 anteriorly in the higher cognate type. 



Under this method, there are the following cases : — 



a. A transfer of members from the cephalic to the locomotive 

 series ; as the transfer of the forelimbs to the locomotive series 

 in passing from Man to Brute Mammals ; that of a pair of max- 

 illipeds or posterior mouth-organs to the locomotive series in 

 passing from Insects to Spiders ; that of two pairs of maxillipeds 

 to the locomotive series in passing from Decapod to Tetradecapod 

 Crustaceans. 



b. A transfer of locomotive or prehensile power and function, 

 more or less completely, from the anterior locomotive organs to 

 the posterior. 



c. A transfer of tlie locomotive function, more or less com- 

 pletely, from the limbs (these often becoming obsolete) to the 

 body, and mainly to the caudal extremity. 



Under 6 and c, the condition may be described as — 



(c*) ProstheniG (from the Greek cr^o, before., and (skvog, strong), 

 if the anterior locomotive organs have their normal superiority. 



(6) Metasthenic (from ^sroj, after, &c.), if a posterior pair is the 

 more important, and the anterior are weak or obsolete. 



(c) UrostheriiG (from ouga, tail, &c.), if the posterior part of the 

 body, or the caudal extremity, is the main organ of locomotion. 



Ordinary flying Birds are prosthenic, while the Pi^cecoces (Galli- 

 naceous Birds, Ostriches, &c.), being poor at flying, or incapable 

 of it, are metasthenic^ and they thus exhibit their inferiority of 

 grade. Hymenopters, Dipters, Lepidopters, &c., among Insects, 

 are prosthenic^ while Coleopters, Orthopters, Strepsiplers, &c., in 

 which the fore-wings (the elytra) do not aid in flight, or but little. 



