16 J. D. Dana on the Classification of Crustacea. 
V. In the opposite extreme of organie beings, the vegetable | 
kingdom, the same principle is illustrated. Plants may be so. 
minute as to have free motion and activity, as in animals. "The 
spores of certain Algz are known to have powers of locomotion, . 
and some so-called Infusoria, are now admitted to belong to the. 
vegetable kingdom. "These are examples of locomotive plants. 
Now, ordinary plants, like Cirripeds, are examples of sedentary 
species, that have outgrown the limits of activity. 'lhe hfe-sys- 
tem of a plant, is in fact sufficient in power to give locomotion 
only to the minute plantindividuals alluded to; and infusorial 
species of plants retain it, as long as they live. But when, as in. 
the Algs, vegetative growth proceeds in the enlargement of the 
minute infusorial spore, it immediately outgrows its activity, and 
becomes a sedentary plant. ln most other plants, the seed have 
never the minute size which admits of motion. 
The mean size of the Entomostracan type was stated to be one. 
line; of the Rotatorial type, one-sixth of a line; and we may add, 
that the mean size of the Plant type—understanding by 5n as 
in other cases, the mean size admitting of the highest activity— 
if deduced from the size of plantinfusoria, would be about one- 
sixtieth of a line. 
We observe, that the smallest size of the perfect Macroura 
(f&rst type) is very nearly the mean size as to length of the ani- 
mals of the second type. So also, the smallest size of the perfect 
animal of the second type (T'etradecapoda) is very nearly the 
mean size of the most perfect animals of the third type; and the 
smallest size of the perfect animal of the third type 1s nearly the 
largest size in the fifth type. 
In order to compare allied animals of different sizes, 1t should 
be noted, that while there is some foundation for the conclusion, 
that under certain limitations, size is a mark of grade, rapidity 
of movement or action should also be considered; and the more 
proper comparison would be between multiples of size and 
activity. 'lhis deduction, is, however, true only in the most gen- 
eral sense, and rather between species of allied groups than those 
of different types. We may occasionally find something like an 
exemplifieation of the law among bipeds, ludierous though the 
idea may be. 
VI. We observe with regard to the passage in Crustacea to 
inferior grades under a given type, that there are two methods 
by which it takes place. 
1. A diminution of centralization, leading to an enlargement of 
the circeumference or sphere of growth at the expense of con- 
centration, as in the elongation of the antennz and a transfer of 
the maxillipeds to the foot series, the elongation of the abdomen 
and abdominal appendages, etc. 
b 
LU 
! 
à 
| 
Pi 
Lj 
P" 
zl 
