INTRODUCTION 



the angle at which the cut is made. In the case of Cerianthus 

 each longitudinal element of the body wall will produce a tentacle 

 at its oral end, no matter whether the cut is at right angles to the 

 longitudinal axis of the animal or is made obliquely. 



Fig. 8. Fig. 9. Fig. 10. Fig. 11. 



Figs. 8 and 9. — Figure 8, diagram of a fresh water planarian from which 

 a piece, achd, is cut. Figure 9, this piece forms a new head at its oral end ac, 

 and a new tail at its basal end. 



Figs. 10 and 11.- — Regeneration of a piece, acbd, cut out obliquely from the 

 planarian. A tiny new head is formed near the most apical corner o of the 

 piece acbd, and a new tail at the most basal corner b. (After Morgan.) 



As a third type we may select a hydroid Tuhularia (Fig. 12), 

 because it introduces a principle of regeneration existing only in 

 living organisms, but not — as far as the writer is aware — in 





Fig. 12. Fig. 13. 



Figs. 12 and 13. — Figure 12, diagram of a normal hydroid, Tubularia, from 

 which a piece, ab, is cut out. P, polyp; R, foot of the hydroid. Figure 13, 

 heteromorphic regeneration of the piece ab, which forms a new polyp at either 

 end. 



crystals. Tuhularia is a sessile marine organism with a long 

 slender body, one end of which — which we will call the foot, R 

 (Fig. 12) — is attached to soUd bodies (rocks or pieces of wood), 



