1. Eggs of Limnae stagnalis were subjected to a heat shock (37° C.) for or 3 hours at the 2-to 4-cell stage. Both exogastrulae and head malformations were produced.

  2. The exogastrulae produced by a heat shock differ considerably from those caused by lithium treatment in showing a much more serious disturbance of development, leading to the appearance of greatly atypical differentiations.

  3. No typical cyclocephalic malformations were produced by this treatment. Apparently a heat shock does not primarily act by depressing the animal gradient field.

  4. Local eye reductions were produced preferentially on the right side. Presumably the left-right asymmetry at early cleavage stages in Limnaea is attended with differences in physiological conditions between both sides.

  5. Lateral eye reduplications, leading to the formation of two eyes in a single tentacle field, occurred on both sides.

  6. The most characteristic heat-shock effect consists in a reduplication of the posterior part of the apical plate, with the formation of a median tentacle field containing an eye, and sometimes a tentacle.

  7. The splitting of the apical plate is not attended with a decrease in the number of apical plate cells, but in at least some of the cases with an increase.

  8. It is concluded that these median reduplications are caused by a strengthening of the animal gradient field, leading to the splitting of the apex of the gradient.

  9. It is possible that the lateral eye reduplications are due to a splitting of a secondary field apex.

  10. Dislocations of head organs, especially of the nervous ganglia, encountered in the treated embryos, show that the differentiation of cerebral ganglion, pedal ganglion, and statocyst does riot depend on the presence of a normal cerebropedal connective on that side of the body.

You do not currently have access to this content.