In the Aurelia of a portion of which the accompanying woodcut (p. 102) is a representation, seven of the lithocysts were removed, while the remaining one was almost entirely isolated from the general contractile tissue by the incisions _aa_, _bb_, _cc_. The lithocyst continued to animate the tissue-area _xxxx_, and through the connecting passage _y_ the contraction-waves spread over the remainder of the sub-umbrella tissue _zzzz_. So far, of course, the facts were normal; but very frequently it was observed that the contraction-waves did not start from the lithocyst, or from the area _xxxx_, but from the point o in the area _zz_. After this origination of the contraction-waves from the point _o_ had been observed a great number of times, I removed the lithocyst. The effect was not only to prevent the further origination of contraction-waves in the area _xxxx_, but also to prevent their further origination from the point _o_, the entire umbrella thus becoming paralyzed. Hence, before the removal of the lithocyst, the contraction-waves which originated at the point _o_, no less than those which originated at the lithocyst itself, must in some way or other have been due to the ganglionic influence emanating from the lithocyst and asserting itself at the distant point _o_. [Illustration: Fig. 21.] This property, which lithocysts sometimes present, of asserting their ganglionic influence at a distance from their own locality, can only, I think, be explained by supposing that at the point where under these circumstances the contractions originate, there are situated some scattered ganglionic cells of considerable functional power, but yet not of power enough to originate contraction-waves unless re-enforced by some stimulating influence, which reaches them from the lithocyst through the nervous plexus. _Regeneration of Tissues._ The only facts which remain to be stated in the present chapter have reference to the astonishing rapidity with which the excitable tissues of the Medusæ regenerate themselves after injury. In this connection I have mainly experimented on Aurelia aurita, and shall, therefore, confine my remarks to this one species.