210 INVERTEBRATE PHYSIOLOGY 



depends on humoral factors. By the transplantation of prothoracic glands, 

 it is possible to induce leg regeneration in adult cockroaches (Bodenstein, 

 1955). Since the adult insect is normally unable to regenerate its legs, re- 

 generation is induced through the agency of the experimentally supplied 

 prothoracic-gland hormone. A certain titer of the hormone is needed not 

 only for the initiation of regeneration but also for sustaining its pro- 

 gression. The responsiveness of the organs to the hormone seems to de- 

 cline somewhat with age, for the adult tissues respond with less ease than 

 the nymphal tissues to the same hormone titer. Nevertheless, the leg of an 

 adult individual can be induced several times to differentiate anew by re- 

 generation, attesting to the amazing plasticity of the formative adult ma- 

 terials. In order to respond with differentiation to the prothoracic-gland 

 hormone, an immature organ has to reach a certain degree of development. 

 The same is observed in regeneration (Bodenstein, 1941). A regenerating 

 moth wing disc has to acquire a definite state of organization before it 

 becomes competent to respond with imaginal differentiation to the pro- 

 thoracic-gland hormone. The close relationship between the processes 

 of ontogeny and regeneration is again evident. 



Before ending this section, it must be mentioned that, in the walking- 

 stick Dixippiis, regeneration seems to be controlled by the corpus al- 

 latum ( Pflugfelder, 1939). Molting and leg regeneration can be induced 

 in the imago by the transplantation of nymphal corpora allata. Since there 

 is little doubt that molting in all insects is under the control of the pro- 

 thoracic-gland hormone and since the prothoracic gland has degenerated 

 in the adult insect, it is difficult to understand how molting in Dixippus 

 is brought about by the implantation of corpora allata. Further experi- 

 ments are needed to clarify this issue. 



REFERENCES 



Bodenstein, D., 1939. Investigations on the problem of metamorphosis. Development 

 relations of interspecific organ transplants in Drosophila. J. Exp. Zool. 82, 1-30. 



Bodenstein, D., 1940. Growth regulation of transplanted eye and leg discs in Droso- 

 phila. J. Exp. Zool. 84, 23-37. 



Bodenstein, D., 1941. Investigations on the problem of metamorphosis. VIII. Studies 

 on leg determination in insects. /. Exp. Zool. 87, 31-53. 



Bodenstein, D., 1943. Hormones and tissue competence in the development of Droso- 

 phila. Biol. Bull. 84, 34-58. 



Bodenstein, D., 1953a. Studies on the humoral mechanisms in growth and meta- 

 morphosis of the cockroach, Pcriplancta amcricana. I. Transplantations of inte- 

 gumental structures and experimental parabioses. /. E.vp. Zool. 123, 189-232. 



Bodenstein, D., 1953b. The role of hormones in moulting and metamorphosis. K. D. 

 Roeder, ed.. Insect Physiology, 879-931. New York. 



Bodenstein, D., 1954. Endocrine mechanisms in the life of insects. Rec. Prog, in Hor- 

 mone Res. Proc. of the Laurentian hormone Conf. 10, 157-182. 



