356 E. W. MACBRIDE. 
circles, whilst the right hydrocele and the right posterior 
ceelom remain small. 
(4) The gradual atrophy of the stalk. 
(5) The outgrowth of the adult cesophagus and the formation 
of the new mouth on the left side. 
In the Crinoid the list would stand thus: 
(1) The constriction of the animal into calyx and stalk. 
(2) The displacement of the mouth and neighbouring organs, 
i.e. the hydroceele, to the posterior end of the body by unequal 
growth. 
(3) The mutual displacement of the right and left posterior 
celoms, the left becoming posterior and the right anterior, 
both having a ring-shaped growth. 
(4) The spiral growth of the intestine and formation of anus 
close to primary madreporic pore. 
It will be seen that the Asterid metamorphosis is very 
different from that of the Crinoid, being much simpler: one 
great difference which strikes one at once being that in the 
former case the ends of the hydroceele grow so as to embrace 
the stalk, which thus appears to spring from the oral surface ; 
whereas in the latter case the hydrocele is carried far away 
from the stalk to the posterior end of the body. Much diligent 
search has been made in the centre of the aboral surface of 
Asterids for traces of a stalk, but to anyone who has grasped 
the foregoing explanation it will be at once obvious how futile 
such search must prove. Pl. 29, figs. 158 and 159, though 
intended to indicate ancestral forms, illustrate the two meta- 
morphoses outlined above very well. 
The sections about to be described illustrating the meta- 
morphosis are nearly all cut parallel to the larval plane, and 
as was the case with the sections of the larva, where two or 
three sections from the same series are figured the most dorsal 
is in every case placed first, and so one can clearly see their 
relation to corresponding sections of the larva. As one always 
thinks, however, of the organs of an Asterid as related to the 
plane of the disc or adult plane, it will be well to repeat the 
relation which these two planes bear to one another. The 
