REGENERATION OF GONAD TUBULES FOLLOWING EXTIRPATION IN THE SEA-CUCUMBER, THYONE BRIAREUS (LESUEUR)

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Abstract
(1) The gonad in the sea-cucumber consists of two major portions: (a) a group of tubules in which germ cells are maturing and (b) a basal portion, the gonad-basis, from which these tubules arise. Failure to recognize this has probably led to the incorrect statements that these forms "will regenerate the gonad." (2) In order to test the extent of the capacity to regenerate gonadal tissue, a partial or a complete gonadectomy was performed upon Thyone briareus (Lesueur). The gonad was exposed by turning the animal inside out after an induced autotomy of its digestive system and anterior end. (3) That this procedure had no very injurious effects is shown by the fact that approximately 95 per cent of the operated animals survived. These and the controls regenerated the autotomized parts as rapidly as did eviscerated but unoperated animals. (4) There was no regeneration of gonadal tissue following complete gonadectomy. (5) If only the tubules were removed, new tubules might arise from a restricted, anterior region of the gonad-basis at a rate four times the normal (at this season). (6) The only histological feature that distinguished this productive region from the rest of the gonad-basis was the presence of nests of germ cells. (7) The possibility that tubule formation is dependent upon the presence of germ cells was suggested by still other facts. No sterile tubules were ever found among the regenerated tubules. Furthermore, the sterile proximal portion of a tubule which sometimes remained after a tubule had been torn out, did not give rise to a new tubule. Finally, when the tubules were roughly torn out, that portion of the gonad-basis containing the germ cells might or might not be lost and this is correlated with the fact that after such treatment, a Thyone may regenerate either a right or a left, or a right and a left tuft of tubules. It is granted, however, that such evidence is not conclusive. Germ cell origin and tubule formation may be independently related to a totipotence possessed by only a few cells in a restricted portion of the gonad-basis for which these experiments provide no test.