In the course of twenty-five days from the operation, the more perfect half could not have been distinguished from any other specimen.

The other had increased much in size; and towards its posterior end, a clear space was formed in the parenchymatous mass, in which a rudimentary cup-shaped mouth could clearly be distinguished; on the under surface, however, no corresponding slit was yet open.

If the increased heat of the weather, as we approached the equator, had not destroyed all the individuals, there can be no doubt that this last step would have completed its structure.

Although so well known an experiment, it was interesting to watch the gradual production of every essential organ, out of the simple extremity of another animal.

It is extremely difficult to preserve these Planariae; as soon as the cessation of life allows the ordinary laws of change to act, their entire bodies become soft and fluid, with a rapidity which I have never seen equalled.
I first visited the forest in which these Planariae were found, in company with an old Portuguese priest who took me out to hunt with him.