THE DEVELOPMENT OF ASTERINA GIBBOSA. 361 
both spaces grow out together underneath the growing lobe of 
the hydrocele, and thus the radial perihemal canal itself is 
formed ; we shall find later that the inner perihemal ring arises 
as an outgrowth from the oral end of the axial sinus or anterior 
coelom, and hence it is marked a’ in the woodcut. 
Fig. 53 shows us that the fourth and fifth lobes of the 
hydroccele have extended over to the right; this being the 
result of the tendency of the two ends of the hydroceele, which 
have become entirely shut off from the anterior ccelom, to 
approach one another. We also see from the obliquity of the 
right posterior ccelom (compare figs. 44—46 with figs. 52 and 53) 
that the lateral flexure of the body on the stalk has commenced. 
The flexure in a downward direction cannot be well shown by 
sections. 
Pl. 29, figs. 54—57, are sections of a larva rather older than 
Stage E. We see that the differentiation of the stalk from the 
body has been initiated by the dorsal constriction of the neck 
of the preeoral lobe. In consequence of this the anterior coelom 
becomes divided into a stalk portion @, and a body portion a’, 
the latter forming the axial sinus. We see, further, that the 
ventral horn of the left posterior ccelom U'p’c’ has pursued its 
growth, extending obliquely to the right under the gut, and then 
upwards in a dorsal and anterior direction, and on its course 
the last of the five arm rudiments appears, viz. V. Fig. 57 
shows the outgrowth of septa destined shortly to close the 
ventral communication between this right horn of the left 
posterior coelom and the anterior coeelom. The primary lobes 
of the hydroccele have each by this time given rise to two 
lateral lobes, the rudiments of the first tube-feet, the primary 
ones themselves being destined to form the terminal tentacles 
of the water-vascular system. 
Figs. 58 and 59 represent a larva about midway between 
Stages E and F. We see the final division of the hydroccele 
from the anterior coelom, the last connection being in the 
neighbourhood of lobe 3, and also the separation of the axial 
sinus from the stalk celom. We see also the remains of the 
larval cesophagus (/e.), which already in Stage E has broken off 
