Regeneration / by Thomas Hunt Morgan.

  • Thomas Hunt Morgan
Date:
1901
Catalogue details

Licence: In copyright

Credit: Regeneration / by Thomas Hunt Morgan. Source: Wellcome Collection.

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    that develops in a piece of this kind appears in the middle of the pos- terior cut-surface, between the old and the new parts. It may extend somewhat obliquely in the new part, and point toward the new tail. If a piece is cut from the anterior part of a worm by two oblique and parallel cuts, the new head appears at one side of the anterior cut-surface, and the new tail at the other side of the posterior cut- surface. The new pharynx appears in the new material of the pos- terior part in the middle line. Thus the middle lines of the new head and tail and pharynx lie in different positions, yet these parts are Fig. 22. — Two upper rows Planaria Ingubris. Lower row Planaria maczilata. Upper row. Tail-piece cut off obliquely in front of genital pore. Figures show mode of regeneration. Middle row. Piece including old pharynx cut off by two cross-cuts, regenerating head and tail. Lower row. Piece cut off as last, regenerating head and tail. subsequently brought into the same line. This is done by the head ex- tending more forward and becoming broader, the tail growing backward and also becoming broader. The old piece becomes narrower at the same time. These three changes going on simultaneously produce a new symmetrical worm. In one form, Planaria Ingubris, the symmetri- cal form is reached largely by the forward growth and the enlargement of the head, and the growth backward and the enlargement of the tail (Fig. 22, B). In Planaria macnlata the old part shifts, so that it forms a new median line connecting the median line of the new head
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