THE DEVELOPMENT OF ASTERINA GIBBOSA. 365 
we observe the incipient bifurcation of the posterior end of the 
pyloric sac (which is formed from the larval stomach) to form 
the pyloric czca. 
Fig. 79 is a section parallel to the adult plane of a slightly 
younger larva; it shows beautifully the mutual relations of the 
water-vascular ring (wv), the axial sinus, and the oral ccelom. 
If one compares this figure with Pl. LV, fig. 53, in Ludwig’s 
paper, one sees at once that his supposed rudiment of the oral 
blood-ring is only the oral celom. Figs. 75 and 76 show the 
completion of the metamorphosis by the apposition of arm 
rudiment No. V covering the tip of the ventral horn of the left 
ceelom (I'p’c’) to hydroceele lobe No. 1. As compared with 
the larva represented in PI. 21, figs. 62—69, we notice the 
much smaller size of the axial sinus (a’). Fig. 75 shows also the 
bifurcation of the anterior end of the pyloric sac into two ceca. 
Comparing it with fig. 76, which is a more ventral section 
from a larva of the same age, we see also that the spaces 
between the pyloric ceca (py) and the aboral body- 
wall are continuations of the right posterior celom. 
Fig. 76 shows also the first trace of ovoid gland (‘ heart”) 
(ov.g.) arising as a ridge of epithelium including blastoccelic 
jelly and fibres and amcebocytes, projecting into the axial sinus. 
By comparing this figure with Pl. 21., fig. 61, the shift of arm 
rudiment No. V can be clearly made out. Figs. 80 and 81 are 
sections parallel to the disc of a larva rather older than Stage G. 
Fig. 80 shows how the oral ccelom almost surrounds the ceso- 
phagus, and also that the axial sinus is commencing to form 
the inner perihemal ring by growth from its lower end (compare 
woodcut). In fig. 81 we see at the point marked * the closing of 
the water-vascular ring by outgrowths from the hydrocele lobes 
Nos. 1 and 5 respectively. We also notice what we have already 
seen in fig. 76, that the septum between the oral ceelom and the 
left posterior coelom is breaking down ; and in fig. 82, which is 
from a young star-fish in which the metamorphosis is just 
complete, we see that from the remnants of this septum the 
retractor muscles of the cesophagus or “ stomach ” are formed. 
The remaining figures on the plate show the finishing touches 
