478 On the supposed Bilateral Symmetry of the Ctenophora. 
place on two symmetrical halves of the body*.” As the animal 
has only two halves, and consequently the two halves with pre- 
ponderating development of parts constitute the entire animal, 
one does not understand where the parts remaining backward in 
their development can find a place. But if we were to under- 
stand by the term “ halves” only opposite parts of the body (and 
one is accustomed to find a perfectly new mathematical language 
in works on natural history), the relation occurring in the Cte- 
nophora, and indicated as in favour of “ bilaterally symmetrical 
type,” would not be any better expressed. Or are the orifices 
of the funnel and the oral lobes preponderatingly developed 
gastric vessels and tentacular filaments, or vice versé? Or are 
our own arms and legs preponderant developments of some parts: 
of our dorsal and ventral surfaces ? 
In his ‘Zoologische Briefe’ +, Carl Vogt has explained, in 
his usual simple and luminous manner, the distinctions between 
radiate and bilateral structure. According to this representation 
of his own, he ought to have indicated the Ctenophora uncon-: 
ditionally as perfectly radiate in their structure. And yet even. 
he has allowed himself to be led astray by the ‘long transverse 
ribbon” of the Cestum Veneris, which, as he remarks in his 
‘Ocean und Mittelmeer,’ “may be divided, by a cut carried 
transversely upon the axis of the band, into two perfectly similar 
halves, in which not the least trace of a radiate arrangement can 
be detected :” it is sufficient te add, “ any more than in an indi- 
vidual ray of any other radiate animal,” in order to show that. 
the indisputable fact proves nothing adverse to the radiate con- 
struction of animal. And if we further indicate that the halves 
_are indeed perfectly similar, that is to say, not merely sym-: 
metrical, but congruent, and that each of them displays a bi- 
lateral arrangement, a peculiarity is pointed out which certainly 
occurs in all biradiate animals, but not in a single bilateral one. 
But are not the Ctenophora, although perfectly radiate animals, 
still, as being bzradiate, more nearly allied to the bz/ateral animals 
than other polyradiate forms, and consequently to be regarded 
as intermediate? I think not. The apparent similarity, existing 
ouly in name, disappears as soon as we exchange “ bilateral” for 
“‘non-radiate.” On the contrary, the smaller the number in 
which an animal or vegetable organ exists, the more certainly is it 
usually retained. And so in this case it might be expected that 
the smaller the number of rays, the more rigidly will the radiate 
structure be carried out, and that a transition into other modes 
of arrangement will occur rather with a high than with a low 
number of rays. Experience confirms this conjecture: leaving 
* Grundziige der vergl. Anatomie, p. 67. 
+ Bd. i. pp. 64 & 65, 
