SHELL OF ECHINUS ESCULENTUS. 215 



complexity of their structure, the diversity of their 

 forms, their incalculable numbers in existing races, 

 the still more innumerable series of extinct genera, 

 or the wonderful attributes with which they are indi- 

 vidually endowed, they will always furnish materials 

 for interesting contemplation. 



How shall we commence our description of an 

 Echinus? We have heard of the journals of conti- 

 nental tourists, in which it is gravely chronicled, that 

 "in this princely collection of pictures there is a 

 Guido measuring 3ft. by 3 ft. 5." We have heard 

 the Thames Tunnel described as having required so 

 many millions of bricks for its construction. We 

 have heard the mosaics in St. Peter's admired on 

 account of the innumerable pieces of various-coloured 

 stones required for the composition of those per- 

 durable monuments but we cannot say that we were 

 much enlightened by such connoisseurship. Let the 

 reader examine for himself with due attention one of 

 these wondrously constructed beings, and then pro- 

 nounce whether among the works of man he has ever 

 seen anything more mathematical in design or more 

 artificial in execution. 



The shell of an Echinus esculentus of moderate size 

 is composed of at least ten thousand distinct pieces, 

 so accurately conjoined that the whole fabric seems a 

 single shell. Upon the exterior of this amazingly 

 constructed dome may be reckoned not fewer than 

 three thousand spines of various sizes, all capable of 

 independent movement. Add to these at least a 

 thousand tubular sucking-discs, instinct with life and 

 motion, not to mention innumerable appendages which 



