350 Dana on the Classification of Animals 
3. Coirdinate grades and distinctions in Classification. 
X. The codrdinate value of subdivisions in the system of 
classification is brought out to view in the parallel columns of 
the preceding tables, and evidence is thence afforded as to what 
groups are rightly designated, classes, orders, etc. 
. We thus learn that the subdivisions of the class of Mam- 
mals—Man, Megasthenes, Microsthenes,—are properly orders, if 
we so call the subdivisions Decapods and Tetradecapods under 
Crustaceans, or Insects and Spiders under Insecteans. 
b ain, we have a solution of the question whether in each 
of the classes, Mammals, Birds, and Reptiles, the hemitypic divi- 
sion, as so-called on page 816, is a subclass codrdinate with the 
typical division of the same, or whether it is an order codrdinate 
with the three higher subdivisions of the class. The question 
appears to be decided, (contrary to former views of the writer,) 
that it is correctly made an order. These hemitypic divisions 
actually correspond severally to the degradational division In 
other columns of the different tables; and, therefore, if in the 
case of other classes, as those of Crustaceans, Insecteans, &c., 
they are orders, so are they in the three classes of Vertebrates 
mentioned. They have also a relation to the hemitypic divisions 
among Fishes, which are the first and second orders of the class. 
— XI. In an inferior or degradational group, the distinctions of 
the subdivisions included are generally much more strongly and 
obviously exhibited in the structure than among typical groups. 
us, the orders of Fishes are based on characters that have 
nearly a class-value among the-higher Vertebrates. In the same 
manner, Amphibians, or hemitypic Reptiles, differ from true Rep- 
tiles more obviously than Odtocoids, or hemitypic Mammals, differ 
from other Mammals. So, the distinctions among the groups of 
Crustaceans are very wide compared with those among Insects ; 
and those among degradational Crustaceans far wider than those 
among the typical subdivisions. The relative force of the life- 
systems is, in all*probability, as great between Odtocoids and 
typical Mammals as between Amphibians and typical Reptiles, 
although so unequally expressed in the structure of the high or 
importance to the structural differences among inferior or de- 
Under any class, order, tribe, the typical Bi Ss oe . 
the degradational. Hence characteristics which separate the 
typical groups frequently separate only subordinate divisions - 
under an inferior or degradational group. Exam es occur in 
the class of Fishes under Vertebrates, in whose subdivisions the 
her classes of Vertebrat artly represent d; in the order 
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