REGENERATION OF THE REPRODUCTIVE SYSTEM FOLLOWING BINARY FISSION IN THE SEA-CUCUMBER, HOLOTHURIA PARVULA (SELENKA)

¹ Dry Tortugas Laboratory, Carnegie Institution of Washington, and Edward Martin Biological Laboratory, Swarthmore College, Swarthmore, Pennsylvania

1. The extreme variation in the reproductive system of large specimens of the sea-cucumber, Holothuria parvula, is investigated by means of dissection and microscopic examination.

2. As a result of frequent transverse fission, specimens are found in three conditions irrespective of the variation in the reproductive system: (I) apparently whole animals, (II) anterior fission halves which are obviously regenerating new posterior ends, and (III) posterior fission halves which are obviously regenerating new anterior ends.

3. Sterility existed in all animals of Group III, but in none of Group I.

4. In small specimens of Group I, the degree of development of the reproductive system is correlated with the size of the animal, but in specimens of medium size or larger all stages in the typical development of the system occur.

The simplest gonad consists of nests of germ cells imbedded in the dorsal mesentery which originate from cells in the hypertrophied left epithelium.

5. Extremely simple gonads and the absence of a gonoduct in large specimens of Groups I and II cannot be attributed to periodic resorption nor to a retarded development related to asexual reproduction, though resorption of the oldest tubules does account for considerable variation in the size of the gonad.

6. It is concluded that the simple gonads in large specimens represent early stages in the late regeneration of the reproductive system within posterior fission halves which have already reconstituted all other systems.

7. The condition of the gonad in Group II shows that no correlation exists between a particular condition of the gonad and the occurrence of fission, and that under natural conditions the asexual mode of reproduction may be repeated without the intervention of the sexual process.