MR. G. J. ROMANES AND PROFESSOR J. C. EWART 
850 
the point of a pencil—the spines alone are able to hold it with wonderful firmness by 
forcing their tips against it on all sides. 
The area thus affected by an ordinary stimulation, such as that supplied by a touch 
with a needle, measures in a longitudinal direction about half an inch. The extent 
of the area affected in a tranverse or latitudinal direction depends upon the point 
stimulated with reference to the ambulacral feet. Midway in an interambulacral 
area the influence extends as far as the double rows of feet on either side ; the feet, 
however, of the inner, or nearer rows, moving more decidedly than those of the outer, 
or further, rows. The spines are rarely affected beyond the area named by a stimulus 
of mere contact, but in the case of the pedicellarise the irradiation of the stimulating 
influence may proceed further, sometimes extending as far as the second double row 
of feet, or ambulacral area, on either side ; the certainty and activity of their move¬ 
ments, however, rapidly diminish with their distance from the seat of stimulation. At 
and near the seat of stimulation, i.e., within the area first named, the certainty and 
activity of their movements are very great, and the period of latency very short; in 
other words, immediately any solid body touches any part of the external surface of 
an Echinus, it is surrounded by all the pedi cellar be in the neighbourhood, while even 
those which are too far away to touch the object will, perhaps for the long distance 
round which we have named, bend towards it. 
2. Physiology of the Pedicellarial— And here we have the proof of the function 
of the pedicellarhe. In climbing perpendicular or inclined surfaces of rock, covered 
with waving sea-weeds, it must be of no small advantage to an Echinus to be provided 
on all sides with a multitude of forceps, all mounted on movable stalks, which instan¬ 
taneously bring their grasping forceps to bear upon and to seize a passing frond. The 
frond being thus arrested, the spines come to the assistance of the pedicellariae, and 
both together hold the Echinus to the support furnished by the sea-weed. Moreover 
the sea-weed is thus held steady till the ambulacral feet have time also to establish 
their hold upon it with then sucking discs. That the grasping and arresting of fronds 
of sea-weed in this way for the purposes of locomotion constitute an important func¬ 
tion of the pedicellarhe, may at once be rendered evident experimentally by drawing a 
piece of sea-weed over the surface of a healthy Echinus in the water. The moment 
the sea-weed touches the surface of the annual, it is seen and felt to be seized by a 
number of these little grasping organs, and—unless torn away by a greater force than 
is likely to occur in currents below the surface of the sea—it is held steady till the 
ambulacral suckers have time to establish their attachments upon it. Thus there is 
no doubt that the pedicellariae are able efficiently to perform the function which we 
regard as their chief function. We so regard this function, not merely because it is 
the one that we observe these organs chiefly to perform, but also because we find that 
their whole physiology is adapted to its performance. Thus their multitudinous num¬ 
ber and ubiquitous situation all over the external surface of the annual, is suggestive 
of their being adapted to catch something which may come upon them from any side, 
