based on the Princij^le of Cephalization. 269 



the system of animal life is either four or three, that is, the divi- 

 sion in each case is either quaternate or ternate. 



II. The lowest of the subdivisions in each group is a degrada- 

 tional or semidegradational subdivision, or hypotypic. 



III. The quaternate division is confined to six cases (excepting 

 two or three among inferior types in which there are two degra- 

 dational subdivisions) : 1, the number of subkingdoms ; 2, the 

 number of classes under Vertebrates, the highest of the subking- 

 doms ; 3, 4, the number of orders under Mammals and Fishes, 

 the highest and lowest classes of Vertebrates ; 5, 6, the numbers 

 of tribes under two of the orders of Mammals. 



IV. In three only of the six cases of quaternate division are the 

 three higher subdivisions all true typical^ namely : 1, in the divi- 

 sion of the animal kingdom into subkingdoms ; 2, of the Verte- 

 brates into classes ; 3, of Mammals into orders. In the last we 

 reach Man. As Man alone is archetypic in the class of Mammals 

 (p. 96), so the Mammal- type is archetypic among Vertebrates, 

 and the Vertebrate-type among the subkingdoms. 



6. Below this archetypic level, in the orders of Mammals, the 

 number of true typical subdivisions is but two — and these are the 

 betatypic and gammatypic ; for the first or alphatypic subdivision 

 in both jNIegasthenes and Microsthenes, as explained on page 96, 

 is hypertypic, and not true typical. 



c. Again, of the four orders of Fishes only one is typical, the 

 two highest being hypertypic (p. 96). 



V. In the rest of the animal kingdom, the number of true 

 typical groups, in the classes, orders, and tribes that have been 

 reviewed, is either two, the betatypic and gammatypic, or one, the 

 gammatypic alone. 



2. Lines of gradation. — Lines of gradation between groups are 

 lines of convergence or approximation through intermediate species. 

 Before mentioning under this head the deductions from the pre- 

 ceding classification (or VIII. and IX. beyond), two general prin- 

 ciples (VI. and VIL), having an important bearing upon them, 

 are here introduced. 



VI. The approximations between two groups usually take 

 place, as has been frequently observed, through their lower limits^ 

 or most inferior species, that is, between the degradational subdi- 

 vision of the inferior as well as of the superior group. — For 

 example, plants and animals approximate only in their simplest 

 species, the Protozoans and Protophytes ; Birds and Quadrupeds 

 most nearly in the Ornithorhynchus or Duckbill — which, at the 

 same time that it is the lowest of Mammals, is related to a very 

 inferior type of Birds, the Ducks ; Quadrumanes and inferior 

 Mammals through the Lemurs of the former and the Bats and 



XEW SERIES. VOL. XIX. NO. II. APRIL 1864. 2 M 



