REMARKS ON THE FIGURES OF PLATE XXXIII. 
THE DUPLICATION OF THE VENTRAL FACE OF THE MAMMALIAN SERIAL AXIS YIELDS A WHOLE STRUCTURE 
OF ANTERO-POSTERIOR AS WELL AS BILATERAL SYMMETRY. 
OR: which is conducted in search of a law of formation, may assert the right of considering 
its subject under all modes of development which can possibly happen within the compass of natural 
operation. When we find that bilateral symmetry is. the effect of the repetition of a side, we then 
reasonably interpret that repetition is the simple cause of bilateral symmetry. When, on the contrary, 
we remark that antero-posterior symmetry does not characterise the form, we then may (even while 
we acknowledge the mechanical design of such a figure) still question the cause of this antero-posterior 
asymmetric effect, and upon finding that the anterior aspect is plus, while the posterior aspect is minus, 
we, under this evidence, attribute the effect such as it is, to the cause such as it appears to be, and 
hence interpret that antero-posterior symmetry may be wanting in consequence of quantity having been 
subtracted from posterior structures. In Nature there happens no one instance of a mixture or combination 
of incongruous or absolutely dissimilar elements. The variety which occurs amongst entities of the same 
system or order, is always occasioned by the metamorphosis of quantity, which, when it appears to interrupt 
the law of order or symmetry for particular fitness, may hence be accounted the natural cause of the 
condition of asymmetry. Now it is true that the skeleton serial axis although manifestly asymmetric 
as to ventral and dorsal faces, still’ instances this condition of development through plus and minus 
quantity ; for which reason, we say that it is not possible rationally to deny that the minus face or 
dorsum may be various to the plus face or venter, simply as the effect of lost or subtracted quantity. 
Thus on one side 
of the median line would happen c, the costal piece articu- 
In fig. A we represent a symmetrical form. The one | this structure into unequal quantities. 
side b, is a repetition of the other side 0, and consequently 
the median line cleaves the form symmetrically. lating with a moiety of the centrum; whereas on the 
In fig. B we represent a symmetrical series of circles in 
double row, and we see that circle 2 is the symmetrical 
homologous opposite of circle 2, and is at the same time 
the serial homologue of circle 1. 
metrical opposite of circle 9, and also stands as the serial 
homologue of circles 1 and 2. If this symmetrical order 
of homologous forms were continued ad infinitum, still the 
character of series would never change ; and even if their 
serial order, thus extended, were carried through the 
regions of space, still the median line a, a, when passing 
through their secant pomts, would divide the series 
So is circle 9 the sym- 
symmetrically. 
In fig. C a vertebra is represented, but the median line 
a, which would divide figs. A and B symmetrically, is seen 
while passing through the centrum of fig. C, to divide 
other side of the median line, would happen d, and a, the 
transverse process and neural arch. If, however, we repeat 
the dorsal structure a, in the ventral structure 0, we then 
see that the repetition of form would create the character 
If again, we describe from 
the costal pieces c, the ventral circle which they them- 
selves usually describe, and if we afterwards repeat this 
ventral circle at the dorsum, then the median line would 
separate homologous circles. Perhaps it may some day 
appear that the archetype form of a spinal axis is a quan- 
tity capable of being thus: cleft into symmetrical halves, 
of symmetry in this fig. C. 
and that the structure which we now name vertebra, is a 
modified proportional of the same archetype. 
Now fig. D is still not capable of being cleft symmetrically 
by the line a, carried through it so as to divide the 
