THE METAMORPHOSIS OF ECHINODERMS. 49 
CruiateD Banvs anp Ruines.—Even before the collapse of 
the stomach the ciliated band of Auricularia shows signs of 
breaking up, at first only by a thinning of the band at certain 
points (fig. 2), and later by its complete separation into seg- 
ments. Many of the changes which follow have already been 
correctly described (21 and 32), but as much has been misun- 
derstood (especially by Semon) it will be better to describe 
the phenomena in full. ‘To simplify this description as far as 
possible I shall begin at the posterior end of the larva, where 
the changes are least complicated ; and with the help of figs. 
3, 4, and 5, the formation of the two posterior (fourth and 
fifth) ciliated bands ought to be easily intelligible. 
It is convenient to divide the ciliated band of Auricularia 
into three regions: (1) an anterior ventral, (2) a posterior 
ventral loop, and (3) a pair of longitudinal bands uniting 
these loops. These will at once be recognisable in any figure 
of Auricularia. In fig. 3 the whole band is outlined, but 
only those parts which persist and form the ciliated rings of 
the pupa are shaded—the dorsal parts (seen through the trans- 
parent tissue) being left lighter than the ventral. It must be 
understood that this arrangement is purely diagrammatic, and 
that the persistent parts of the band do not admit of accurate 
delimitation. 
Fifth (posterior) Ciliated Ring.—This is usually 
formed from the two lateral (right and left) pieces of the 
ciliated band, which form the junction of the longitudinal 
bands with the posterior ventral loop (fig. 3, V) ; sometimes, 
however (for a short time time only), each piece is further 
divided into a dorsal and a ventral portion. ‘The two halves 
(right and left) soon acquire a more transverse arrangement 
(figs. 4 and 5), and finally completely encircle the posterior 
end of the body, the anus having meanwhile assumed a terminal 
position. 
Fourth Ciliated Ring.—This is invariably formed from 
four pieces (figs. 3 and 4, 1V). The dorsal and ventral por- 
1 It is convenient to distinguish between the ciliated band of Auricularia 
and the ciliated rings of the pupa or “ barrel” stage. 
vou. 38, PART 1.—NEW SER. D 
