THE DEVELOPMENT OF ASTERINA GIBBOSA. 247 



we observe the incipient bifurcation of the posterior end of the 

 pyloric sac (which is formed from the larval stomach) to form 

 the pyloric cgeca. 



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 {wvr), the axial sinus, and the oral ccelom. 

 If one compares this figure with PI. IV, fig. 53, in Ludwig's 

 paper, one sees at once that his supposed rudiment of the oral 

 blood-ring is only the oral ccelom. 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 

 ccelom {I'p'c') to hydroccele lobe No. 1. As compared with 

 the larva represented in PI. XIV, figs. 63 — 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 caeca. 

 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 caeca (py) and the aboral body- 

 wall are continuations of the right posterior ccelom. 



Fig. 76 shows also the first trace of ovoid gland ("heart") 

 (ov.g.) arising as a ridge of epithelium including blastocoelic 

 jelly and fibres and amoebocytes, projecting into the axial sinus. 

 By comparing this figure with PI. XIV, 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 oeso- 

 phagus, and also that the axial sinus is commencing to form 

 the inner perihsemal 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 hydroccele lobes 

 Nos. 1 and 5 respectively. We also notice what we have already 

 seen in fig. 76, that the septum between the oral coelom and the 

 left posterior coelom is breaking down ; and in fig. 83, 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 oesophagus or "stomach" are formed. 

 The remaining figures on the plate show the finishing touches 



