2OO 



LEMON. 



[VOL. I. 



at least the following forms : Tubularia mesembryanthemum, 

 Aglaophemia pluma, Plumularia pinnata, Eudendrium (rasimo- 

 sum ?), Sertularia (polyzonias ?). 



Bickford and Driesch, 1 cited by Morgan, have also shown 

 that in the tubularian hydroids two heads may develop on 

 opposite ends of a piece cut from a stem, especially if the 

 piece be short. 



3. Pseudoheteromorphosis. By cutting a narrow strip from 

 any part of the body so as partly to isolate it, a posteriorly 

 directed head may be developed by the reversal of the piece. 



FIG. 10. 



FIG. ii. 



FIG. 13. 



FIG. 14. 



FIG. io. The lines a show the nature of the cuts which produced heads at right angles to the 



body. 



FIG. ii. A worm with heads lying at right angles to the main body. 

 FIG. 12. Pseudoheteromorphosis. 

 FIG. 13. The lines a, b, and c represent the cuts made to induce regeneration of heads in the 



tail region. 

 FIG. 14. A head regenerated on one of the tails. 



If by tension and growth this position becomes permanent, 

 forms are produced which, to the casual observer, appear to be 

 marked examples of heteromorphosis. Figs. 8, 12, 15, and 16 

 possess all the outward appearances of true heteromorphosis, 

 but by the aid of Figs. 6, io, and 13 one can readily show that 

 there is neither the reversal of axial relations nor the develop- 

 ment of orie organ for another. Hence we do not have true 

 heteromorphosis, but simply the swinging around of a portion 



1 " Experimental Studies of the Regeneration of Planaria maculata," Separat- 

 Abdruck aus dem Archiv fitr Entwickelungsmechanik dcr Organismcn. Bd. vii, 

 P- 382- 



