90 HENRY BURY. 
his paper as fully as the obvious care bestowed upon it deserves, 
but the following is a brief summary of its main points: 
The ancestor has a hydrocel with eight tentacles sur- 
rounding the mouth (which is ventral) and two symmetrically 
disposed body-cavities. It then becomes fixed by the tentacles 
of the right side, three of which are thereby suppressed; and 
after this the point of fixation shifts to the centre of the right 
side, while the mouth (surrounded by the five remaining ten- 
tacles) moves into the left side. 
In this way he arrives at an arrangement of the body-cavities 
and mesentery with relation to the alimentary canal which I 
believe to be very nearly correct; but the steps by which this 
position is reached are open to grave objections. In the first 
place, there is no sort of evidence that more than five tentacles 
ever existed. Biitschli begins with ten, but afterwards reduces 
them to eight, with suppression of three, for the sole purpose 
of explaining the remarkable bilateral symmetry observed by 
Lovén in EKchinids. For the details of this explanation reference 
must be made to the original paper; but as we have no sort of 
evidence that this symmetry extends to other groups, I venture 
to think that the assumptions made to explain it are wholly 
unwarranted. Of fixation by the right side there is no more 
embryological evidence than of the fixation by the dorsal side 
assumed by Semon; but the whole assumption of universal 
fixation is founded mainly on paleontological evidence (6, p. 137), 
to which I shall return later. 
In addition to these more important assumptions, there are 
many other points unsupported by evidence (e. g. the pulling by 
the cesophagus of a part of the right body-cavity into the 
oral side—see p. 146; and the derivation of one of the five 
permanent tentacles from the right side—see p. 157, note), as 
well as others in which serious distortion of evidence occurs. 
Thus he accepts Ludwig’s determination of the position of the 
anus in Crinoids, in preference to mine (since proved by See- 
liger to be correct), because it agrees with his theory 
(6, p. 156), regardless of the evidence I produced in my last 
paper to show that in other Echinoderms also the anus was 
