vol.i.] Torrey— Mery . — Regeneration in Sagartia Davisi. 221 



The difference between the two sets of experiments lies in the 

 facts that according to tli<' firsl set, 25 per ceut of the polyps cut 

 from the mouth toward the foot disk, across the mouth, divided 

 as against 25 per rent of those cut from the foot toward the 

 mouth, perpendicular to the major mouth axis, and thej divided 

 more rapidly; while according to the second set, none of the 

 polyps cut across the mouth toward the foot disk divided, 

 although 50 per cent of those cut from foot toward mouth, per- 

 pendicular to the major mouth axis, did divide. This discrepancj 

 may disappear with farther experimentation on larger numbers 

 of polyps and with especial care to keep the wounds open. 



It appears to be clear, however, from these experiments, that 

 an interruption of the physical continuity of two portions of a 

 polyp by means of a cut parallel with the course which would be 

 taken by a normal fission plane, tends to interfere with the 

 physiological interaction of the separated regions and initiate 

 the process of fission. This is especially true when the cut 

 follows the aboral-oral course of the normal fission plane (second 

 set of experiments. ) 



Double structures have been produced in various animals by 

 similar experiments: in Hydra notably by Trembley, in plana- 

 rians by Duges, Morgan, Van Duyne and others, in lizards by 

 Tornier. The partial separation of the first two cells of the sea 

 urchin (Drieseh) and Amphioxus (Wilson) leads to even more 

 marked results.* In all of these cases, normal physiological con- 

 nections have been broken; Morgan is disposed to believe that 

 these physiological connections are in the shape of some sort of 

 tension. The doubling of parts, however, never involves the 

 entire body; there is no evidence of a stimulus to division. Per- 

 il aj is this is because division of the types made possible by the 

 experiments does not occur normally in any of the species con- 

 cerned. Yet in Gorymorpha palma, separation of the two indi- 

 viduals developed heteromorphically on the opposite ends of a 

 fragment of stem lias been observed; the discontinuity between 

 the two ends shown by the development of two hydranths was 

 further emphasized by the subsequent division, which never 

 occurs under normal conditions. 



*See Morgan, ('01) for an account of these cases and the 

 subject. 



