and boring marine animals. 
347 
to time, by the adhesion of sand to the tentaculee when 
thrown out in quest of prey. The gluten exuding from the 
tentacular cements the grains to each other and to the tube. I 
have very often known these branches to be formed by the 
animals I kept in confinement. 
The Spatangus buries itself in the sand by the action of its 
bristles : those on its under surface are short and thick, 
diverging from the centre towards the circumference ; and at 
their extremities becoming expanded, flattened and curved, 
with the convexity downward. Around the sides they are 
straight, longer, but much slighter than the others, dimi- 
nishing in thickness towards their extremities ; and, in the 
state of inaction, resting flat upon the body, with their points 
directed backward. A few long stout spines arise in a cres- 
cent from the back, which converge till their points meet. 
All are attached to the crest individually by a small mus- 
cular papilla. 
The flat bristles have a limited rotatory motion, and ad- 
mit also of being moderately depressed : the lateral ones 
are extended nearly to a right angle with the body, and are 
directed downward, even beyond the perpendicular : the 
long dorsal spines admit only of being erected to the per- 
pendicular, or reclined backward to a moderately acute angle 
with the body. 
The operations of the animal are best observed by placing 
it on the sand immediately after it has been dug up, as it 
soon perishes out of the water The motion of the short 
flat bristles forms in a little time, a quicksand under it, into 
which it sinks by its own weight so far as to enable the lowest 
of the lateral bristles to act upon the sand. These are 
