* 
J. D. Dana on the Classification of Mammals. 69 
The GYRENCEPHALA include, in Prof. Owen’s system, three 
groups—I, the Unguiculata (consisting, as presented by him, o 
the orders 1, Quadrumana, 2, Carnivora); I], the Ungulata (1, Ar- 
tiodactyla, or Ruminantia, 2, Perissodactyla or Solidungulata 
and Multungulata, 8, Proboscidia, 4, Toxodontia); III, the Mu- 
he Crustaceans have here also afforded the writer the princi- 
ples of classification on which he rests his conclusions.’ 
€ orders among Crustaceans are based not only on a dif- 
ference of structure and cephalization, but also on a difference 
in the normal magnitude of the life-system. The Decapods are 
built on a life-system of large size as to plan as compared with 
that of the Tetradecapods. Deducing the relative size from the 
mean dimensions of the active species under the two types, the 
ratio is lineally as 4:1. (See the papers of the author already 
ferred to.) Moreover, while thus distinct, the subdivisions of 
the two orders form parallel series—the Brach 
8 
ural Tetradecapods and the Amphipods, Macroural.’ — 
rl he life-system in the Entomostracans is on a still smaller 
an, : 
Among the viviparous Mammals (exclusive of Man) the first 
8roup differs from the second on this same principle—the fact of 
meet and more powerful type of structure or life-system. 
's fact stands out boldly to view on comparing active species 
Ange iteiples are none the less important because indicated among these lower 
fhe clates. The turns of a closed spiral are easily mistaken for circles, as was long 
“se with those of flowers in plants; but if the spire be drawn out long, it then 
its true are otherwise undi 
exhibits cha’ me si 
racters and may display details that are ot ver- 
nna € class of Crus ine ‘cxstnpes of a type of structure thus drawn out— 
and yn’ Tanging fr ic mem Rotifer to the highest crabs, 
the a genera are distributed, so to s in the course of 
; $ k, tant 
i €s, since they are com tively few in number. Fundamental principles 
peresi eet coe Be therefore exhibited in this class on a magnified scale, easily 
and understood. 
Macee nllelism is complete: for the Amphipods differ from the Isopods just as 
ede from ang saeco in having a larger and less cosines Seid, 
beating sh larger mouth-organs, longer segments to the body, and an elongated foot- 
abdomen ; all, points of inferior concentration and cephalization, 
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