Miscellaneous. 69 
through two successive phases: the first would correspond to the 
form A; but, in consequence of the resorption of the large central 
chamber, the animal would construct a series of new chambers corre- 
sponding to the form B. 
In all the species examined exact measurements have shown us 
that, supposing the central chamber to be absorbed, the space set 
free between the first serial chambers of the form A is large enough 
to allow the modified chambers of the form B to be developed. 
It now remains for us, before pronouncing in favour of one of 
these two hypotheses, to trace a living species through all the phases 
of its evolution.— Comptes endus, May 28, 1883, p. 1598. 
On Radial and Bilateral Symmetry in Animals. By H. W. Conn. 
The relation of radial to bilateral symmetry among animals is 
a question in regard to which there has been considerable discussion. 
It is, however, today pretty generally acknowledged that the type 
of radial symmetry must have preceded that of bilateral symmetry. 
Two important views are current as to the origin of a bilateral form 
of symmetry, such as is presented by the group Vermes, from a radial 
symmetry, such as we find in the Coelenterata. The simplest view, 
of which Ray Lankester is an exponent, is as follows :— 
Starting with a radially symmetrical larva, this view supposes 
that the two forms of symmetry arose with reference to the stationary 
or locomotive life of the animal. On the one hand, the stationary 
animal retains its primitive radial symmetry and grows into a 
radiate adult. On the other hand, the locomotive larva is modified 
by its free life. Its growth, in order to give greater freedom of 
motion, results in an elongation of the body in a direction parallel 
with its axis. Such a long cylindrical body would of necessity 
soon develop swimming-organs; and these swimming-organs, in 
order to give greater steadiness of motion and prevent an inconve- 
nient revolution of the body, would appear in such a position as to 
give the animal an upper and an under surface, and consequently a 
bilateral symmetry. With the continued elongation of the body, 
the digestive tract, which at first ended blindly, also would elon- 
gate and finally acquire a posterior opening at a position directly 
opposite the mouth. This view, then, supposes the body of the 
radiate animal to elongate in the direction of its long axis, and a 
bilateral symmetry to arise in reference to the organs of locomotion. 
A second view, advanced by Balfour, while based on the same 
fundamental principle of stationary and free life, supposes the change 
to take place in a different fashion. This view supposes that the 
growth of the free-living radiate form resulted in an elongation, not 
in the direction of the axis of the animal, but rather at right angles 
to this axis. This places the mouth of the animal, from the first, 
not at one extremity but upon one side, which therefore becomes 
very early the ventral side. The swimming-organs afterwards arose 
in reference to the already indicated bilateral symmetry. 
