104 HENRY BURY. 
is in the same interradius as the water-pore (see fig. 24) before 
metamorphosis. A further indication that this was the primi- 
tive position of the anus is given by its relation to the calcare- 
ous plates in Ophiurid Plutei. No doubt these plates (which 
mark the radii) are precociously developed, but their situation, 
when we compare this larva with Bipinnaria or Brachiolaria, 
points pretty clearly to the conclusion just arrived at. On 
the position of the anus in adult Asterids and Echinids, much 
nearer the aboral pole than the water-pore, I shall have some 
further remarks to offer later on. 
Of course this question of the situation of the anus, though 
interesting, has no vital bearing upon my hypothesis; it is 
important, indeed, that the general course of the intestine 
should be parallel to the plane of the water-vascular ring, 
and that in early stages of ontogeny it should lie at the level 
of the equatorial zone (mesentery); but the anus may be placed 
in any interradius that ontogeny demands—that is simply a 
question of the length of the intestine. In my diagrams I have 
made it long, so as to bring it into the interradius of the 
water-pore ;! but it would have been quite as easy to shorten 
it into the interradius which it occupies in Asterids, or still 
further into that in which it is found in adult Kchinids. 
We saw that a straight course for the water-tube from water- 
pore to water-vascular ring, which is demanded by the anatomy 
of all known Echinoderms, was inconsistent with the very 
simple movement of this ring into the left side which I had 
postulated ; and we must now examine how the observed posi- 
tion may have been brought about. 
Seeliger (39, p. 261) takes up the somewhat remarkable 
position that the water-pore is not in the same interradius in 
all Echinoderms, giving as evidence the fact that it is in the 
middle dorsal line in Holothurians (which is not strictly true), 
but far removed from it (on the left side) in the larva of 
Antedon. In making this statement, however, he seems to have 
forgotten the fact that, before the pore appears, the body-cavi- 
1 A slight alteration of my drawing has brought it into a radial position in 
fig. 48, 
