582 E. W. MACBRIDE. 



SO that the thin-walletl, scoop-like portion of the (^esophagus 

 has been pushed completely over to the right and very much 

 diminished in size. In fig. 4 !• c the lobes of the left hydrocoele 

 are seen to project as the primary tentacles into the outer 

 and ventral part of the stomodajum. The left posterior 

 coelom has meanwhile developed two extensions which may 

 be termed the dorsal and ventral horns (fig. 44 a, I", j)'' . c", 

 and figs. 44 h and c, I'. lY. c'). Of these the first extends 

 forward along the left side of the oesophagus outside the 



Text-fig. 2. 



c:^ 



A /^ /\ 



f 



P ii d^ 



A series of diagrams to show the clianges undergone by tlie occlom. r/. 

 Single coeloniic rudiment, b. Riglil and left eoeloniic sacs. c. Left 

 cocloniic sac preparing to divide, d. Left sac divided, right pre- 

 paring to divide, e. Both sacs divided. /. Formation of liydro- 

 coeles (indicated by heavy lines), ff. Further development of hydro- 

 coele, and of left posterior ccelom. 



lobes of the hydrocoele, but only reaches as far forward as 

 the second lobe. The second reaches across to the right side 

 of the larva. Eventually the two meet and complete the 

 ring form of the left posterior coelom, outside and parallel to 

 the ring of the hydroccele. A precisely similar develop- 

 ment takes place in Asterina gibbosa, and in Echinus 

 csculentus the front end of the left posterior coelom 

 grows in a ring-form round the stone-canal and axial sinus. 

 The intestine becomes diminished in size and pushed over to 

 the right ; meanwhile its cells commence to develop large 



