Page:The third Huxley lecture.pdf/27

23 On the other hand, when the animal was at the palest, the pigment granules were massed together into a circular disc, which did not occupy the whole of the body of the cell, being apparently grouped round its nucleus, while the offsets and their ramifications were quite colourless. Any intermediate degree between these extremes of complete diffusion and perfect concentration of the pigment granules might occur, with corresponding differences in the tint of the animal.

Camera Lucida sketching here stood me in good stead. I doubt if anyone would have credited my description had I not been able to support it by such evidence. For here was a function entirely new to physiologists. In muscular contraction the entire mass of the cell shrinks, and in ciliary action, the only other visible form of motion then known to occur in animal tissue, the part concerned moves as a whole, so far as we are able to observe it; in the pigmentary changes the form of the cell remained unaltered, but one of its constituent materials was seen to be transferred from place to place among the rest. But drawings made with the camera of a cell in successive stages of concentration of the pigment admitted of only one just interpretation.