386 MR PATRICK GEDDES AND MR FRANK E. BEDDARD 
February 1881, Messrs RomAnEs and Ewart, in the “Croonian Lecture for 1881,” 
an abstract of which has just been published,* describe a complete nervous 
supply to the spines and the pedicellariz. This consists of delicate fibres 
connecting small bipolar cells, and reaches the mandibular muscles ; in several 
preparations they observed delicate fibres which appeared to end in an epithelial 
pad on the inner surface of mandible. This nerve plexus was traced into con- 
nection with a sub-epithelial nerve plexus on the body wall. 
With a view of elucidating the structure of the soft parts, we have studied 
in detail those of the large sea urchin, Echinus sphera (Forbes). This species 
has four kinds of pedicellariz, in the description of which the names intro- 
duced by VALENTIN will be replaced by their English equivalents, as is commonly 
done by British naturalists. Each pedicellaria consists of two parts—a 
“head ” and a stalk—both of which contain a calcareous skeleton and associ- 
ated soft parts. The skeleton of the stalk is a rod which articulates on to a 
tubercle on the surface of the test ; the skeleton of the head consists of three 
valves, which are articulated together, and are capable of approximation and 
divarication by means of muscles. The soft parts consist of (1) a layer of 
epithelium covering the whole pedicellaria ; (2) muscles attaching the base of 
the calcareous rod to the test ; (8) muscles of head arranged in three masses 
connecting together the three calcareous valves, and serving to approximate 
them by their contraction ; (4) muscles connecting the base of the valves with 
the top of the rod. Other curious structures will be reserved for description 
until the different kinds of pedicellariz come to be dealt with severally. 
The ophiocephalous pedicellariz are by far the most abundant variety, and 
occur scattered all over the test in company with the other varieties, and also 
on the buccal membrane in a thick ring surrounding the mouth. In this situa- 
tion, however, they differ slightly ; the muscular mass between the top of the 
rod and the base of the valves is shorter, and the calcareous valves themselves 
are rather broader in proportion to their length, but in other respects they 
agree with the ophiocephbalous pedicellariz of the test. 
The whole surface is covered with a layer of epithelium which some 
observers have supposed to be ciliated, and shows, on treatment with nitrate 
of silver, nucleated cells of a polygonal contour (Plate XX., figs. 2, 3). 
The calcareous rod which supports the stalk is attached to a tubercle on 
the surface of the test by a number of muscular fibres, which show no signs of 
transverse striation. The rod itself is of a uniform diameter except at the 
proximal end, where it dilates slightly, and at the distal end where the muscles 
of the stalk are attached. It is made up of a series of minute cylindrical rods 
which are joined here and there by transverse pieces, giving the whole structure 
* Romanes and Ewart, “Observations on the Locomotor System of Echinodermata,” Proceedings 
of the Royal Society of London, March 1881. 
