476 nt M. F. Miller on the supposed - 
of these four halves might at pleasure be united to form a com- 
plete animal. 
_ Every plane carried through the middle of a ray, as also every 
divisional plane between two rays, divides even-rayed animals 
into bilaterally arranged halves. The halves of a bilateral ani- 
mal, considered separately, are no longer bilaterally arranged. 
The series of these characters which separate sharply and 
abruptly the radiate from the bilateral arrangement of the animal 
body might readily be carried much further. I break it off 
here; for already I hear the question, What is the use of this 
idle enumeration of self-evident differences between things which 
no one can confound together? Is it not sufficient to have seen 
a starfish by the side of a crab, or even merely to hear the de- 
nominations radiate and bilateral, to prevent our ever doubting 
which of the two modes of arrangement we have before us? 
This may be supposed, but evidence to the contrary is furnished, 
amongst other things, by the Ctenophora. According to all 
the characters adduced, and however the idea may be other- 
wise analyzed mathematically, they appear to be radiate and, 
indeed, biradiate animals, and exhibit this structure stamped in 
the most perfect regularity and most rigidly followed throughout, 
without the slightest trace of a transition to bilateral arrange- 
ment; and yet the prevailing opinion of the day appears to be 
in opposition to this. Burmeister expresses himself with cau- 
tious doubt :—‘ The Ctenophora appear to be constructed upon 
both types, yet a regular oval form predominates*.” Others 
regard them positively as “ bilaterally symmetrical animals,” or 
as a transition-form “from the radiate type to the bilaterally 
symmetrical.” These are the views of Agassiz}, Vogt, and 
Gegenbaur. The weighty suffrages of such opponents urged 
me to a somewhat detailed exposition of the subject, in itself cer- 
tainly extremely simple. With this exposition of the differences 
between radiate and bilateral animals my evidence in favour of 
the position of the Ctenophora among the former is already given. 
It remains for me to discuss the reasons for the opposite opinion, 
which, unfortunately, I cannot find brought imto connexion in 
any work accessible to me. 
The first inducement to regard the Ctenophora as bilateral 
animals, or as intermediate between these and radiate animals, 
has probably been furnished by “the laterally compressed” 
form of the body of many species, and especially the greatly 
elongated ribbon-like form of Cestum, in which Vogt finds the 
“symmetrical type” most distinctly displayed, and Gegenbaur 
considers that “the bilateral symmetry attains its culminating 
* Geschichte der Schopfung, 6. Aufl. p. 330. 
j According to the ‘ Jahresberichte’ of V. Carus and Leuckart. 
