THE 
AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[THIRD SERIES.] 
Art. XXX.- On Cephalization ; by James D. Dana. Part V. 
Cephalization a fundamental principle in the Development of 
the System of Animal Life. 
The principle of cephalization has been explained at length 
in memoirs in former volumes of this Journal,* and to them I 
would refer for detailed illustrations of the subject. Among 
these illustrations the attention of the reader is especially 
called to those from the department of Crustacea, the study of 
which-occupying more than half of my time between the years 
1837 and 1855-brought before me the facts on which it rests. 
It cannot fail to be perceived, in the review, that, with ele- 
vation in grade among the Decapods, for example-passing 
upward along the line of Macrural forms to the Brachyural (or 
from the lowest of shrimp-like species to crabs)-there is in 
general, with the rising grade, an abbreviation relatively of the 
abdomen, an abbreviation also of the cephalothorax and of the 
antennae and other cephalic organs, and a compacting of the 
structure before and behind; a change in the abdomen from 
* For former papers on Cephalization, see this Journal, IT. xxii, 14, 1856; 
xxxv, 65, xxxvi, 1, 159, 321, 440, 1863; xxxvii, 10, 157, 1864; xli, 163, 1866. 
One point made in these papers, I would withdraw, viz: that the transfer of 
the anterior pair of members in Man from the locomotive to the cephalic series is 
analogous to the transfer which takes place in Crustaceans in passing from the 
Tetradecapod to the Decapod type, or from the Arachnoid to the Insect type. 
The latter is plainly a structural transfer, the two anterior pairs of limbs in the 
Crustacean, or the one in the Insectean class, becoming, by the transfer, strictly 
cephalic organs (pertaining to the mouth series), and existing thus in a large tribe 
of species. But in man it is properly only a functional transfer, analogous to cases 
among spiders and Tetradecapods, where the anterior legs become adapted to 
serve functionally the mouth or head, without that structural transfer which would 
place them of itself in the higher order. 
Am. Jour. Sen-Third Series, Vol. XII, No. 70.-Oct., 1876. 246 
J. D. Dana-Cephalization a fundamental principle 
an organ of great size and power and chief reliance in locomo- 
tion, to one of diminutive size, and no locomotive power; and a 
change as to the particular pair of legs which is the strongest, 
from one of the more posterior to the anterior in the series; in 
other words, that, as grade rises, there is abbreviation behind and 
before, and thus a concentration of the structure, and a more 
forward or anterior position in the stronger of the organs of 
locomotion and prehension. The shrimp and crab are so widely 
unlike in form that the common eye hardly suspects that they 
are made up of the same parts or organs arranged in precisely 
the same order: that the latter is only a shrimp contracted in 
length, dwindled to almost nothing in its abdomen, and com- 
pacted in its mouth organs so that the outer pair makes a well 
fitting operculum over the others, and shortened in its very long 
multiarticulate antennae to a few articulations giving them a 
length often not a tenth of that of the cephalothorax. 
I would refer also to the case among mammals, for an illus- 
tration of the same principle-that the lowest forms are those 
having their locomotive functions located in the posterior parts 
of the body ;* and that in the higher, the forces, or force-organs, 
are more and more forward in the structure. For example, in 
the whale-the tail is the propelling organ and is of enormous 
power and magnitude, and the brain is very small and is situ- 
ated far from the head extremity in a great mass of flesh and 
bone furnished with poor organs of sense; a grade up, in the 
horse or ox, the tail or posterior extremity is no longer an 
organ of locomotion, and is little more than a caudal whip-lash, 
and locomotion is performed by organs situated more anteriorly, 
the legs, and a well-formed head carries a brain which is a 
vastly higher organ of intelligence than that of the whale-but 
the legs are simply organs of locomotion, and the hinder are 
the more powerful; and higher up, in the tiger or cat, the 
fore-legs-not the hind-legs-are the organs of chief muscular 
force, and these have higher functions than that of simple loco- 
motion, and, further, the body is proportionally shortened, and 
the head is shortened anteriorly or in the jaws and approxi- 
mates thus toward the condition in man. The existence or not 
* The fact that fishes have, with few exceptions, the tail as the chief or only- 
locomotive organ, corresponds with their inferior position among Vertebrates. 
At the same time, it makes the application of the principle of cephalization in 
determining grade among them quite difficult. In most classes or groups the 
force-organs constitute a series along the body, and the position of the strongest, 
and the transfer forward with the rise in grade, is openly manifested. But in 
nearly all fishes, the tail remains the locomotive organ, with no transfer of its locomo- 
tive function to more anterior members, and, therefore, other less obvious and 
much less certain modes of determining any forward transfer of force are all that 
remain. And, further, as the conclusions we may arrive at hold good, among all 
classes of animals, only in case other conditions in the structure are essentially equal, 
the inferences from such evidence can ordinarily extend only to the grade in 
the family or smaller group to which the species belong. in the Development of the System of Animal Life. 
247 
of a switch-like tail, as in ordinary quadrupeds, has little bear- 
ing on the question of degree of cephalization, since the organ is 
not an organ of locomotion, or one indicating a large posterior 
development of muscular force. But, approaching man in the 
system of life, even this seems to have significance. 
In accordance with the principle and method illustrated, 
animals of a given type differ widely as to the conditions and 
arrangements for action-muscular, sensorial and psychical- 
in the animal structure. In the low,* there is, usually, large 
size and strength behind, an elongation of the whole structure, 
and a low degree of compactness in the parts before and behind; 
in the high, there is a relatively shorter and more compacted 
structure, a more forward distribution of the muscular forces 
or arrangements, and a better head; and the progress in grade, 
under a type, is progress along lines from the former condition 
toward the latter, that is, progress in the strength, perfection 
and dominance of the anterior or cephalic extremity; in a word, 
it is progress in cephalization. 
The principle of cephalization is thus fundamental because, 
first, the chief center of nervous power or energy in an animal is 
at the cephalic extremity; and, secondly, because form in na- 
ture's species is, with some limitations, an expression of force.* 
Again, I have exemplified, in my memoirs, the corresponding 
fact that progress in cephalization generally attends progress in 
embryonic development; referring, for illustration, to the loss 
of the locomotive tail in the frog and many other Amphibians 
at the time of the passage to the adult stage, and the concurrent 
development anteriorly of limbs, with the perfecting of the head 
in structure and senses ; to a similar abbreviation posteriorly in 
the development of modern gars; to the fact that the higher 
insects rise from a state that is worm-like in form, having no 
distinction of thorax and abdomen and sometimes furnished 
with abdominal locomotive appendages, to an adult stage in 
which the abdomen is greatly dwindled in size, the thorax and 
abdomen are distinct segments and the former alone has loco- 
motive members and these of perfected structure, and the well- 
defined head has highly developed sense-organs and exalted 
senses; and to other examples, all illustrating the view that 
through the developments going forward in the progress of em- 
bryonic development, there may in general be distinguished a 
cephalization, or forward improvement, of the structure. 
It has also been illustrated that the geological progress in the 
life of the world has been progress in accordance with the prin- 
ciple of cephalization, this being manifested in the succession 
of forms under the various types, and also in the correspondence 
* For a consideration of the inferior species of some groups, related to half- 
developed embryonic forms in structure, I would refer to my former papers. 248 
J. D. Dana-Cephalization a fundamental principle 
so often exhibited in a general way-as announced by Agassiz 
-between the biological succession and embryonic develop- 
ment. I need not dwell on the facts in this place, as they are 
well understood. 
Professor Marsh has recently brought forward facts which ex- 
emplify fully the view that the succession in the animal life of 
the globe has been more or less connected with brain-progress, 
facts which sustain strongly the doctrine, which I have else- 
where urged, that this progress involved changes in structures 
in obedience to the principle of cephalization.* 
Professor Marsh states! that in the Eocene Dinoceras, from the 
Rocky Mountain region, the brain was not more than one-eighth 
the bulk of that of the modern Rhinoceros-its nearest recent 
ally; in the Miocene Brontotherium it was much larger, about 
equalling that of the Indian Rhinoceros; and in a Pliocene 
Mastodon, the brain was larger than in Brontotherium, but not 
equal to that of living Proboscidians. In a paper on the Eocene 
Coryphodon of the same region,! the brain was even lower than 
in Dinoceras. Again, after a further study of the subject,§ and 
a comparison of an extensive series of ancient and modern 
crania, he gives as his conclusions-in advance of a full and 
illustrated memoir on the subject: "First, all Tertiary Mammals 
had small brains; secowl, there was a gradual increase in the 
size of the brain during the age; third, this increase was mainly 
confined to the cerebral hemispheres, or higher portions of the 
brain; fourth, in some groups the convolutions of the brain 
have become more complicated; fifth, in some, the cerebellum 
and olfactory lobes have even diminished in sizeand, further, 
''there is some evidence that the same general law of brain- 
growth holds good for birds and reptiles from the Cretaceous 
to the present time." 
A growth of eight fold in bulk since the early Tertiary is 
enormous, vastly exceeding in amount the growth in other 
organs; in fact, the species related to the Rhinoceros have not 
increased in bulk with the progress of time, but diminished. 
And the same is true of other species ; there is in general higher 
grade with smaller bulk. Moreover, concurrently with the change 
in the brain, there has been in succeeding species a relative 
shortening of the head and especially of the jaws, besides other 
modifications, such as mark a rising grade of 
* Author's Manual of Geology, 1874, p. 596. 
f This Journal, III, viii, 66, 1874, and xi, 163, with figures of the Dinoceras 
brain; xi, 335, with figures of the brain in Brontotherium; and xi, 425, with 
figures of the brain in the Eocene Coryphodon. 
| Ibid., xi, 425, 1876. § Ibid., xii, 61, July, 1876. 
The jaws are in some mammals relatively short through the incisor portion 
being imperfectly developed, and this condition is a mark of inferior grade. The 
shortening referred to above is not of this degradational kind, but that presented in 
a diminished distance between the normal incisor-extremity and the normal position 
of the posterior molar-an abbreviation which reaches its extreme limit in man. m the Development of the System of Animal Life. 
249 
But have other peculiarities of the later species any connection 
with this growth and change of brain ? We can hardly doubt, 
that, inasmuch as there has been no corresponding change in the 
animal's bulk, there must have been concordant changes some- 
where, and change of equal magnitude and importance; and 
the supposition that they included the structural modifications 
which mark the line of species from the early Tertiary onward, 
does not appear to be extravagant. 
Such growth or progress in the brain and nervous system- 
the seat of power in the animal-is accordant with, and conse- 
quent upon, the great fact that this is the part of the structure 
which comes into actual contact with outside and inside nature. 
It is the means in an animal by which communication is had 
with the outer world and also with its own inner workings and 
appetites; that which takes impressions, which feels whatever 
inspires energy, prompts to action, exhilarates, or exalts; the 
part, therefore, which must grow whenever circumstances favor 
progress, and, at the same time, fail to grow or dwindle under 
unfavorable circumstances; which communicates whatever it 
receives to the being to which it belongs, and, in each case, to 
the part or parts responding to its condition; which reaches 
every part of the system and dominates in all action and growth, 
and hence must cause an expression of its own condition in 
some way on the structure; which, moreover, must ordinarily 
produce correlate changes in correlated parts, if any, because in 
its own nature and distribution the system of correlation has a 
full expression. Energetic use gives increasing strength to 
muscle ; and that wonderful strengthening growth in the brain 
since Eocene times may also have come from use. 
It would hence appear that a prominent means of change in 
species is the action of influences on the brain ; that the brain 
grows and changes and sends its changing forces through the 
animal; and that this gives progress, or degradation ; and hence 
it is that progress is exhibited in cephalization, and degradation 
in decephalization. The brain could not grow to the adult stage 
in the frog without the change in the structure that cotempora- 
neously takes place; and no more could the brain of a species 
like a shrimp grow into a brain of the higher grade of a crab 
without its determining in some sense a concordant higher 
grade of structure in the animal, involving the loss of locomo- 
tion in the abdomen and also other changes. 
We recognize, as evidence of upward progress in Man, an in- 
creasing height, width and erectness of the forehead, and a 
shortening of his jaws, and see therein evidence of improved 
intellect; which means higher grade of cephalization. But, 
more than this, the erect form of Man, the shortened arms, the 
naked skin, as well as the large, smooth-surfaced cranium, may 250 
J. D. Dana-Cephalization. 
also be as directly and necessarily connected with, and depen- 
dant upon, his superior degree of cephalization in the system 
of animal life; while the hairy skin, the long arms, the crested 
skull, the inclined posture of the man-ape, may be all involved 
in the ape's inferior degree of cephalization. If so, the devel- 
opment of the brain in Man and of all the highest structural 
perfections of the Vertebrate type which he exhibits is incon- 
sistent with the existense of the hairy covering and some other 
circumferential as well as interior characteristics of the brute. 
We may therefore believe that in all progress in grade, 
upward or downward, there was involved some changes in the 
animal structure of the kind expressing degree of cephalization. 
Brain-progress could not have taken place without structural 
progress: and with the brain eminently the growing organ, the 
brain-progress would have had a determining relation to the 
latter. More than this, many peculiarities of form or structure 
in animals which are not evidently marks of grade in cephali- 
zation, or have little or nothing to do with it, may have bad 
the same source. The type of structure characteristic of a 
group of species is beyond doubt connected with some peculi- 
arity of chemical composition, or rather of chemical compounds 
present, in the great center of activity ; and this chemical con- 
dition once established, the progress afterward, connected with 
brain growth or change, might well be a development in that 
line of type structure, displaying the type under new forms. 
I do not mean to imply, in the above, that the method of 
progress pointed out accounts for the existence of the various 
types of structure in the animal kingdom, or for all the devel- 
opments under them : but only that, whatever the types of 
structure in course of development, there was also a general 
subordination in the changes to the principle of cephalization ; 
because the nervous system by its growth and domination must 
necessarily have determined such subordination ; and, further, 
that, through the same agency, the development of other pecu- 
liarities of structure and form, not obviously marks of grade, 
may have been occasioned. The origin of the grander types 
of structure must be connected with the profoundest of molec- 
ular laws; and how connected, man may never know. 
These views may hold whatever be the true method of evolu- 
tion. The method by repeated creations through communica- 
tions of Divine power to nature should be subordinated, as 
much as any other, to molecular law and all laws of growth ; 
for molecular law is the profoundest expression of the Divine 
will, the very essence of nature; and no department of nature 
is without its appointed law of development. But the present 
state of science favors the view of u progress through the deri- 
vation of species from species, with few occasions for Divine IT. A. Anthony-Electro-magnetic Machine. 
251 
intervention."* If then there has been derivation of species 
from species, we may believe that all actual struggles and rival- 
ries among animals, leading to a "survival of the fittest," must 
tend, as in Man, to progress in cephalization, and dependent 
structural changes. In fact, mere living, the surmounting of 
the daily obstacles in getting food and shelter and satisfying 
ordinary desires, may have given growth to the brains and 
structures of the Eocene mammals, aiding, but perhaps exceed- 
ing, all other influences from environments. 
The source of variation here pointed out is not at all at vari- 
ance with Darwinism. Darwin, in fact, does not aim to 
explain the origin of variation among species, but chiefly the 
workings of natural selection-variations being in progress by 
some means-in leading to the "survival of the fittest" of the 
varieties. Variation he refers to environments, and especially 
to action on the genital system. The genital system may have 
this prominence in plants; but for animals I would give the 
nervous system the higher place, inasmuch as upon it environ- 
ments make their first and most powerful impress. 
One reason why plants present but few simple types of struc- 
ture compared with animals, and why marine plants are almost 
the same for all geological time, and thus strongly contrast 
with the immense diversity and complexity of types and kinds 
among marine animals, may be found in the fact that plants 
possess not that feeling, knowing, outreaching and inworking 
thing, a nervous system. This, however, is not all: for the 
presence of so large a proportion of nitrogen in the animal 
structure, in addition to other elements, gives an opportunity 
for a vastly wider range of chemical combinations. 
* This sentence is cited from my Manual of Geology, 1874, p. 603. After it come 
these words:-"For the development of Man, gifted with high reason and will, 
and thus made a power above Nature, there was required, as Wallace has urged, 
the special act of a Being above Nature, whose supreme will is not only the source 
of natural law, but the working force of Nature herself," and this I still hold.