Page:Popular Science Monthly Volume 71.djvu/472

466 but existed in the earth-worms, and even among vertebrates; for he it was who discovered that if the head of an earthworm be cut off, the worm will form a new head with a new brain and a new mouth. He first discovered that if you cut off the tail of a salamander a new tail will grow out. He it was, moreover, who discovered that this power of replacing the lost part is greater in the young—greater in the earlier stage than in the later. This indicates in a general way the nature and process of regeneration. We have many kinds of regeneration; we may have that of the single 'cell or that of the whole organism.

We pass now to the next of our slides, which represents a creature of the kind called Stentor. It is a single cell. Here is the nucleus of

the cell; its protoplasmic body is large, and something of the structure of this I have told you in a previous lecture. A German investigator, Professor Gruber, has succeeded in dividing one of these Stentors, a unicellular creature, animalcule, common in fresh water, into three parts in such a method of cutting as is illustrated by the figure on the left. Each of the three parts will then restore itself and become a complete Stentor. In such experiments the protoplasm over the nucleus begins to grow; gradually the original form is again assumed; the creature grows larger and larger, until each piece acquires the parent size, and, so far as we can see with the ordinary microscopic examination, identically the parental structure. That which was lost