360 CALIFORNIA ACADEMY OF SCIENCES. [Peoc. 3D Ser. 



EXPLANATION OF PLATE XXI. 



Fig. I. Cross section through the oesophageal region of a polyp in process 

 of approximately equal division. D, D' ', directives. 



Fig. 2. Single case of transverse division of the mouth; surface view. 



Fig. .3. Three sections through the oesophageal region of a dividing polyp, 

 to show the oral-aboral longitudinal division of the siphon- 

 oglyph. 



Fig. 4. Two sections through the (Esophageal region of a diglyphic polyp, 

 the plane of division passing through one siphonoglyph. 



Fig. 5. Similar to fig. 4; division of the oesophagus completed. 



Fig. 6. Probably a diglyphic polyp originally, the plane of division having 

 passed through both siphonoglyphs. 



Fig. 7. A colony of three individuals, sectioned through the oesophageal 

 region of each individual. 



Fig. 8. Section through the oesophageal region of a dividing diglyphic 

 polyp. 



Fig. 9. Oral surface-view of the angle between two polyps — A and B — 

 formed by division; the lines indicate the bases of the mesen- 

 teries seen through the transparent wall. 



Fig. 10. A typical bud. 10a, cross section of the parent above the bud 

 (indicated at B)\ 10b, cross section of the bud; 10c, indicates 

 diagrammatically the relation of the bud to the parent; both 

 seen in profile. 



Fig. 11. Diglyphic polyp with bud. 11a shows cross sections of the parent 

 and bud. D, D\ directives of the parent; d, d\ directives of 

 the bud; c, pair of complete mesenteries derived from an incom- 

 plete pair just above it in the parent. 11b, looking through the 

 mouth of the bud from within the oesophagus of the parent; s, s, 

 siphonoglyph of parent; r, ridge dividing siphonoglyph s trans- 

 versely into two portions; e, c, edges of a cut across the oesoph- 

 agus of the parent to the mouth of the bud. 



Fig. 12. Colony of four individuals. 12a, A, parent; B, bud on A; C, D, 

 individuals formed by division of a second bud on A; 12b, cross 

 section of A, at the level of xy\ 12c, cross section of C, D\ cor- 

 responding numbers indicate corresponding mesenteries in these 

 two sections. 



