10 J. D. Dana on Megasthenes and Microsthenes. 
type, there are examples among the hres and Macroura, which 
ave all the highs attributes of the species. There are also Amphipo- 
da and Iso ree inches in length, with full vigorous powers. Among 
ilshibeten ‘the Calanide, apparently the highest group, include spe- 
cies that are three lines long, or three times the length of the mean type. 
“TIT. But the limit of efficient activity may be passed; and when so 
it is attended with a loss of active powers. - u ture, s in the fe- 
ale Bopyrus and Lernzoids, and the Cirripeds, outgrows "This res 
the proper sphere of action of the te of fore t 
fentarics on the Cirripeds. 
“IV. Size is, ieeralore an important element in the system of animal 
structures. As size diminishes, in all departments of animal life, the 
he same seems to be the case among Crustacea. The Decapod, as the 
size diminishes, Ce the lowest limit; and then, to continue the range 
of size in species, another structure, the Tetradecapodan, is instituted; 
and as this last has also its limit, the Entomostracan is introduced to con- 
tinue the het soa fae as oe end, the Rotatoria begin. Thus Crus- 
.tacea are made to es, from a length of nearly two feet S 
two hundred sid fifty Hines) ag the t of a one-hundred-and- papi o 
e. These several types of structure among Crustacea do not graduate, 
size, directly from one to another, but they constitute ove 
pling lines, as has been sufficiently shown.” 
While on this rip lies of life-batteries, the writer would sug- 
gest that the grand dynamical distinction between Mollusks and 
Articulates may be this: 
A Mollusk corresponds to a quantity-battery, but one of very 
weak force; that is, it is analogous to a galvanic battery of to 
or three small pairs, at the most. This is indicated, i 
several in the one Apa es thora ganglion, as in 
In the highest Soles ag és halopods (Cuttlefish, a 
the Invertebrate quantity-ba et peatien its greatest power. 
Vertebrates also ap rrespond to a paantiny- belie 
one shown b of the split of of the nervous system); but 
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