CCELOMIC SACS 



FIG. !. SECTIONS THROUGH ONE OF THE 

 ENTEROCCELA (a Scyphistoma polyp) 



TO SHOW THE SACCULATION AND CON- 

 TINUITY OF THE ARCHENTERON AND 

 THE TWO PRIMARY CELL-LAYERS. 



ec, ectoderm, and en, endoderm, indi- 

 cated by dark and pale shading re- 

 spectively. A, sagittal section of the 

 diblastula embryo without oral aperture ; 

 B, similar section of the young polyp 

 after fixation but without oral aperture, 

 s, oral in-sinking (stomoda?um) ; g, rneso- 

 glcea. C, young polyp with mouth, sp, 

 junction of stomodseum and archenteron ; 

 m, gastric pouch. D, transverse section 

 taken so as to cut the gastric pouches 

 (m) above their openings into the archen- 

 teron ; s, stomodiBum. E, a similar 

 section at a later period when four 

 pouches have been formed, st, septa. 

 F, transverse section at a lower level, 

 showing the continuity of the gastric 

 pouches with the axial portion of the 

 archenteron ; t, taeniolaa. (After Goette, 

 from Korschelt and Heider.) 



FIG. 2. SECTIONS THROUGH THE LARV.E OF AN ECHINODERM (Asterina gibbosa) AT SUC- 

 CESSIVE STAGES OF GROWTH ; A, B, C, TO SHOW THE ORIGIN OF THE CO.LOM AS A PAIR 

 OF ENTEROCCELOUS POUCHES. 



El, Blastopore ; D, archenteron ; Vp, vasoperitoneal sacs or coelomic pouches, r and I, 

 right and left sides. (After Ludwig, from Korschelt and Heider.) 



