ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
881 
forms, having such much smaller grasping organs, might at first appear to be of no use 
in grasping sea-weeds. That they are not of so much use in this respect as the 
tridentes is rendered obvious by experiment ; and therefore we do not doubt that 
these pedicellarise are proportionally of more service than the tridentes as general 
cleansers. We cannot say that we have ourselves observed any actual evidence of 
such being the case ; but the interesting experiments of Mr. Sladen (which were not 
published till our observations had been completed) leads him to “ offer it as a sugges¬ 
tion” that “the ciliary epithelium is altogether insufficient” to keep the general sur¬ 
face clean, and that “the duty devolves upon the pedicellarice globiferce, the following 
being the manner in which the work is performed :— 
“ When the tactile cushion of the pedicellarise comes into contact with a tangible 
object of foreign matter, the valves close and a discharge of mucus takes place'"' where¬ 
with the obnoxious object is covered. When the hold of the jaws is again relaxed, 
the irritating substance remains entangled in a cloud of the glairy exudation, ready to 
be easily disengaged from the surface of the animal by a few movements of the neigh¬ 
bouring spines, and is finally carried off by the ordinary currents of the water in which 
the Echinus lives. 
“ A similar process may be observed with the greatest ease to be carried out by 
Astropecten; and this I have been able to verify many times by placing a specimen 
of the common A. aurantiacus in a large flat vessel, convenient for observation, and 
when covered with sea-water sprinkled some fine sand and mud over its dorsal area. 
In the course of a short time most of this will have been carried away by the action of 
the paxillse and by the lateral papiilated grooves, whilst such particles as have resisted 
this operation will be found enveloped in a glairy pellicle, which is gradually and by 
very slight motion drawn into a narrow band extending over the median line of each 
ray. This is then disengaged from the surface entirely, and is finally cast off by the 
slightest movement the Star-fish may make.” 
Postscript. 
[Received December 2, 1881.] 
Since this paper was sent in there has been a note published by MM. Geddes et 
Beddard in ‘Gomptes Ptendus’ (tom. xcii., pp. 308-10) on the histology of the muscular 
tissues of Echinoderms. According to the observations of these authors the conflicting 
views of previous observers on the question whether the muscular fibres of Echinoderms 
are striated or unstriated, admit of being reconciled by the fact that the same muscle 
fibres are sometimes unstriated and at other times appear to be striated. 
* Mr. S laden is bere describing tbe functions of pedicellarise globiferse in a particular species of Echinus 
(SjoTiorecliinus granularis ) where such a discharge was found by him to be very copious. 
MDCCCLXXXI. 5 X 
