AMPHIDOTUS CORDATUS. 291 



following remarks I will try, as briefly as possible^ 

 to narrow the question. 



A very interesting paper by Mr. W. P. Sladen 

 shows that in a Mediterranean species of the same 

 genus the slime is secreted in sacs belonging to the 

 pedicellarise, but no such sacs or secretions have as 

 yet been recorded in connection with the pedicellarise 

 of any British species. 



This Sea-Urchin is common all round our shores. 

 It burrows in the sand to a depth of five or six 

 inches, and keeps a small free opening from itself 

 to the surface, through which pass long processes 

 in search of food. The first thing that is noticed, 

 when one of these Urchins is dug out of the sand, 

 is how clean it is. The spines are all smooth and 

 free from impurities ; not a particle of the running 

 wet sand in which they are imbedded is to be seen 

 among them. 



By a series of experiments I found that the animal 

 has the power of throwing out a large quantity of 

 mucus to relieve itself of any offensive matter that 

 might assail it. In this way it is able to protect 

 itself from the intrusion of the sand; and in all 

 likelihood, by the same secretion, it keeps open the 

 small passage between itself and the surface. 



To endeavour to find the source of the secretion, 

 one of the above species, newly taken from the sand, 

 was put into spirits. When immersed the spines 

 made no motion, but soon became greenish ; nor was 

 the spirits in any way altered beyond being tinged 

 by a little colour extracted from the animal. By 

 this treatment no mucus was thrown out. Another 

 was put into fresh water ; and in a short time 

 mucus was thrown out copiously, quite covering the 

 spines. Its quantity appeared to be nearly equal to 

 the amount of water usually contained in the animal. 

 Suspecting that there might be some conversion of 

 fluids, I drew the water from the shell or test of 

 one of the animals, and put it into two clear glass 

 phials. The water thus taken was a little whitish. 



