[ 82!) ] 
XIX. The Croonian Lecture — 
Observations on the Locomotor System of Echinodermata. 
By George J. Bomanes, M.A., F.R.S., and Professor J. Cossar Ewart, M.D. 
Received Mai’cli 5,—Read March 24, 1881. 
[Plates 79-85.] 
PART I.—MORPHOLOGY. 
§ 1. Ambulacral System. 
1. Holothttria. —When a longitudinal incision is made through the perisome of a 
Holothurian ( Holothuria communis ) there is generally seen escaping, along with the 
branches of the respiratory tree and genital gland, a long sacculated tube filled with a 
fluid, and holding in suspension a large quantity of a brick-dust coloured pigment. 
This tube, which may be one-and-a-half times the length of the entire animal, and 
from one line to half-an-inch in diameter, is the polian vesicle (Plate 79, fig. 1 , a). 
On following it upwards it is found to open freely into a wide circular canal (Plate 79, 
fig. 1 , b) a short distance from the termination of the stone canal. From this circular 
canal five lozenge-shaped sinuses (Plate 79, fig. 1 , c) project forwards, and from each 
of these two large oval sinuses (Plate 79, fig. 1 , d) run forwards parallel with each 
other, the ten oval sinuses becoming continuous with the hollow stems of the tentacles 
(Plate 79, fig. 1, e). In a Holothurian 8 inches in length, exclusive of the tentacles, 
the lozenge-shaped sinuses, which may be designated the sinuses of the circular canal, 
measure a quarter of an inch from above downwards and a little more from side to side. 
From around the pointed upper ends of the canal sinuses the five longitudinal muscular 
bands take their origin. 
When a solution of Berlin blue is injected into the polian vesicle, the circular 
canal and its sinuses, the oval sinuses and tentacles, the radial canals, pedicels and 
ampullae are rapidly distended; but, unless the pressure be kept up for a considerable 
time, none of the coloured fluid penetrates into the stone canal, and either the vesicle, 
ring, or one of the sinuses gives way before it reaches the madreporic plate. If one of 
the radial canals be divided while the injection is being proceeded with, the coloured 
fluid at once escapes, and the tension within the polian vesicle, the circular canal, and 
the tentacles is diminished. If plaster of Paris be substituted for the solution of Berlin 
blue, a cast is readily obtained of the circular canal and its sinuses, but the plaster 
does not find its way either into the sinuses of the tentacles or into the radial canals. 
