280 CRUSTACEA, ECHINODERMS, ETC. 



together. Of these, five rows are perforated, and 

 through these perforations minute suckers are pro- 

 truded. They can be elongated when injected with 



Fig. 212. 



Echinus climbing up side of an aquarium by means of its ambulatory 



suckers. 



water, which is strained off from the sea and ad- 

 mitted to the interior of the sea-urchin through a 

 special plate called the " madreporiform tubercle." All 

 these rows of feet protrude through the needle-like 



