STUDIES ON THE PHYSIOLOGY OF RECONSTITUTION IN PLANARIA LATA, WITH A DESCRIPTION OF THE SPECIES

¹ HULL ZOÖLOGICAL LABORATORY, UNIVERSITY OF CHICAGO

1. Planarie lata possesses a short posterior zoöid and undergoes fission. Fission does not interfere with sexual maturity, probably because the level of fission is far posterior to the genital pore.

2. Susceptibility decreases from the anterior to the posterior end of the first zoöid and increases again with approach to the posterior zoöid.

3. Head frequency varies in relation to level of body in the same way as susceptibility. The differences in head frequency at different levels increase as length of piece decreases, and head frequency is slightly lower in young than in old animals.

4. Isolation of pieces is followed immediately by a great increase in susceptibility, CO₂ production, and oxygen consumption, then a gradual decrease occurs during 12-24 hours to a level still far above that of whole animals. Later a gradual increase coincides with the progress of reconstitution.

5. The increase in susceptibility after section in relation to body level and length of piece varies inversely as the susceptibility gradient of whole animals and the head frequency in reconstitution.

6. The factors determining whether a piece shall or shall not develop a head become to some extent effective within a few hours after section.

7. The experimental data all support the conclusion that in P. lata, as in P. dorotocephala, two factors are concerned in determining head frequency: one the rate of metabolism in the cells at the cut surface, being positive or determining; the other the rate of metabolism in other regions of the piece, being negative or inhibitory. Head frequency in any particular case is determined by the relation between these two factors. Apparently the inhibitory factor is less effective in the shorter pieces and at more posterior levels in P. lata than in P. dorotocephala.

8. The physiological analysis of reconstitution agrees with observations on behavior in indicating that P. lata is a less highly specialized form than P. dorotocephala.