ORGANIZATION AND GROWTH 205 



I shall have to continue the experiments before I can 

 discuss the conditions which determine the formation of 

 these abnormalities. 



IV. ON THE INTERNAL CAUSES OF ORGANIZATION IN 

 TUBULARIA MESEMBRYANTHEMUM 



1. In most animals at a cut edge with a definite orienta- 

 tion only one kind of organ originates. If the tail of a 

 lizard or a salamander is amputated, only a tail and not a 

 head is regenerated in its place, and a lobster develops a new 

 pincer in place of the one lost, and never anything else. 1 

 Nor can it be said that only the higher animals show this 

 inflexibility in organization. As shown by all the experi- 

 ments which have been made upon it for a hundred and fifty 

 years, Hydra behaves thus; even in Infusoria Nussbaum 

 found such a relation to exist between the new growth and 

 the orientation of the wound. 2 In plant physiology the 

 instances in which complete control of organization through 

 external forces is possible are very scarce. In the majority 

 of these experiments, also, it seems that internal, and at 

 present unknown, factors essentially determine the position 

 of the organs. If we wish to control these internal con- 

 ditions in animals, we must try to obtain further information 

 concerning them through experiments. In order to give the 

 reader a clearer idea of the rOle of these internal causes in 

 animal morphogenesis I will remind him of the experiments 

 upon Cerianthus membranaceus, given in the first volume of 

 my Physiological Morphology? The oral pole a of Cerian- 

 thus differs markedly morphologically from the aboral pole b 

 (Fig. 52). To be brief, I will mention only one difference 

 that tentacles arise from the oral pole. If a rectangular piece 



1 This is no longer correct. Herbst has shown that in Crustaceans in the place 

 of an eye a new eye or a new tentacle can be produced at desire. [1903J 



2 M. NUSSBAUM. Archiv filr mtkroskopische Anatomie, Vols. XXVI and XXIX. 



3 See Part I, p. 115. 



