THE METAMORPHOSIS OF ECHINODERMS. 59 
true position; but even this does not wholly account for this 
peculiarity. 
AurmmentTARY Canat.—Although in stage A the mouth is 
much narrowed, yet it retains throughout this stage its ventral 
aspect. With the beginning of stage B, however, it follows 
the inward movement of the hydrocel ring, and turning 
slightly inwards from the ventral surface, is bent upwards and 
towards the left side; in effecting this change it drags in not 
only the thick ectodermic ring derived from the ciliated band 
(21, pl. ii, fig. 16) but also some of the transparent tissue 
surrounding it, and an atrium is formed, lined by ectoderm. 
The aperture of this atrium is at first fairly large, but it 
rapidly narrows, and passes up the left side of the larva towards 
the anterior pole; in doing so it gets further and further 
away from the mouth, and the atrium in consequence increas- 
ing in size, more of the transparent tissue becomes involved 
in its formation. 
The stomach is sharply contracted at the onset of meta- 
morphosis, diminishing to about half its original diameter ; and 
its internal surface is consequently thrown for a time into 
strong folds. Otherwise it undergoes no important changes. 
The intestine in Auricularia occupies a position which 
is nowhere else met with in Echinoderm larve, being directed 
downwards and backwards (figs. 1 and 2), instead of, as in 
all other cases, running forwards along the ventral surface of 
the stomach. 
In stage A a small cecal pouch usually (but not invariably) 
appears at the base of the intestine, running forward from the 
junction of the latter with the stomach. larly in stage B 
this part of the intestine widens rapidly, and its opening into 
the stomach is shifted to the left side. In this way the cecum 
of the previous stage is transformed into a short transverse 
intestine (fig.5; and 21, pl. u, fig. 16), from the right side 
of which the original, posteriorly directed intestine runs back 
to the anus, which is still median. 
This transverse intestine rapidly increases in size, and 
becomes slightly bowed, its anterior margin being strongly 
