aliment cry canal, the entire oesophageal cavity being 

 surrounded b^r ectoderm. 



In "B" the hydrocoele communicates with the 

 posterior enterocoele by a wide opening and at the 

 sane point in "C" the two structures are still in 

 in communi cation, but the connection has been narrow- 

 ed down to a small tube .Fig 7./jc, . 



Beside this connection with the posterior ent- 

 erocoele, a second tube has been formed joining the 

 left anterior enterocoele with the hydrocoele .Fig. 7. si 

 This new tube, which is the rudiment qS; the stone 

 canal, enters the hydrocoele at the same point with 

 the tube connecting the latter with the posterior 

 enterocoele . 



The left anterior enterocoele lies to the left 

 of the oesophagus and dorsal to the left half of the 

 hydrocoele. Fig. 6 a: 7. aol . 



It is to be noted that, although we now have a 

 larva possessing both hydrocoele and stone canal, 

 there has be?n as yet no pore canal formed. This is 

 a marked reversal in the sequence of the formation 

 of these structures from what might be expect 3d from 

 the order of their appearence in other known echin- 

 oderms; the pore canal arising usually before the for- 

 mation of the hydrocoele, while the stone canal appears 

 much later than either. 



