THE METAMORPHOSIS OF ECHINODERMS. 83 
and it seems to me not improbable that most of this coiling of 
the intestine is secondary, and that the original condition was 
that found in Crinoids—a simple curve round the disc, begin- 
ning and ending in interradius A. 
Lovén’s figure of Gonocidaris canaliculata (12, pl. iii, 
fig. 10) is suggestive of this; but of course the matter can 
only be settled by careful study of the development, for which 
I have not been able to obtain the necessary material. 
D. OPHIURIDs. 
For a general account of the external changes which an 
Ophiurid Pluteus undergoes before and during metamor- 
phosis, I must refer to my former paper (5, p. 26) ; here I shall 
only call attention to those features which will be referred to 
in the second half of this paper, in connection with the phylo- 
geny of the group. 
Though not perhaps a very primitive group in themselves, 
their Plutei offer us, in their external features at least, what 
seems to me to be a much more accurate epitomeof phylogenetic 
history than is met with in other Echinoderm larve. Unfortu- 
nately, however, the difficulty of obtaining satisfactory sections 
is so great that few of the internal changes can at present be 
followed in detail. Iam full of confidence that better methods 
will give all the facts we require, as all my material was used 
up before I adopted the celloidin-in-paraffin method, which has 
given me such satisfactory results elsewhere ; but meantime I 
must content myself with inferences from studies of the exterior 
and from our knowledge of other Echinoderm larve, which, 
though attaining to great probability, are never so satisfactory 
as direct observation. 
The first stage in development which we need pause to con- 
sider is that shown in 5, fig. 4. In it the hydroccel forms a 
nearly complete ring round the cesophagus, while the posterior 
part of the body still retains its primitive bilateral symmetry ; 
the plane of the hydroccel is in fact about at right angles to 
that of the mesentery. 
I have already described and figured the changes of position 
