ECHINUS. 305 
and 22, gl.s.), which lies outside the skeletal piece, and 
is bifid at its distal end in many cases. This sac has a 
glandular epithelium (gl.ep.), and is invested by a layer of 
circularly disposed muscular fibres (mg.). Near the apex 
of the sac is a minute aperture (ap.). On the inner face 
of each blade, just above the level of the adductor muscles, 
the ectoderm forms a projecting cushion (tc.). The cells ~ 
forming this stain deeply, and, in addition to cilia, are 
said to bear tactile hairs. A nerve (nf.) passes upwards 
along the inner face of each blade, and its fibres become 
continuous with the filiform basal ends of the cells form- 
ing the cushion. 
The function of the pedicellariz has been the subject of 
much speculation and experiment. Romanes* concluded 
from his experiments that they assist locomotion by 
seizing foreign objects and holding on until the tube-feet 
can be brought into play, but he does not discriminate 
between the different forms. Other observers have re- 
garded them as organs adapted to the capture and con- 
veyance to the mouth of small animals, such as worms, 
Crustacea, &c., to be used as food. Others again have held 
that they are employed in freeing the neighbourhood of 
the anus from feeces, and the spines and test from injurious 
foreign particles. Prouhot found that the glandular pedi- 
cellarize of Strongylocentrotus lividus were used to repel 
the attacks of hungry starfishes. It has been noticed that 
when a soft bodied animal, such as Aplysia punctata, 
comes in contact with an Echinus it always carries away 
with it a number of the glandular pedicellarie. 
In addition to spines and pedicellariz, the plates of the 
ambulacra bear a number of minute knob-like organs, 
which project freely from the surface of the test. These 
* « Jelly-fish, Starfish, and Sea-urchins,” Int. Sci. Ser., vol. L., p. 253. 
+ Comptes Rendus, CXI.:(1890), pp. 62—4. 
