Page:Popular Science Monthly Volume 75.djvu/349

Rh instances their action is independent of nervous control, while in others it is under this control. In my opinion the instances of independent action represent a primitive state; the others a condition brought about through the appropriation of these organs as end-organs by a developing nervous system.

If what has been stated in this article is correct, we must picture to ourselves as steps in the evolution of the nervous system not only the independent origin of muscle around which the nervous organs subsequently develop, but also the independent origin of other effectors such as chromatophores, glands and phosphorescent organs and the secondary appropriation of many of these by a developing nervous system. This principle of appropriation I believe to be as significant in elucidating the present condition of the nervous system and its appendages, as the principle of evolutionary sequence of parts, muscle, sense organ, and central nervous organ, as given in the first three articles.