46 



NATURAL HISTORY. 



duces but a single adult, but before arriving at the adult condition many 

 of the species pass through most wonderful changes. Who would recog- 

 nize this peculiar-looking animal as the young of a starfish or as having 



anything to do with one ? and yet it is. On the 

 side a young starfish is soon to grow out, grad- 

 ually absorbing all of the old larva, and then 

 changing directly into the adult. 



The common starfish on our shores have but 

 five fingers, but below the lowest tides there are 

 many other kinds. In some of the so-called sun- 

 starfish the central disc is much larger, and it is 

 fringed with shorter arms set as thickly as possi- 

 ble, so that the resemblance is close to the con- 

 ventional -figure of the sun. In others the disc is 

 enormously developed and the arms are scarcely 

 noticeable, — the starfish is but a pentagonal disc, 

 and still it shows all the essential characters of 

 its more regular relatives. Not all of these forms 

 feed on shell-fish, for there are some which fill 

 their stomachs with mud ; and in these there is 

 no necessity for that protrusion of the digestive 

 apparatus which is found in oar common form. 



The economic importance of the starfish is com- 

 paratively slight. They are of no value as food or 

 Fl ^f fis rw?trSs°t f ^s y M«? m any other way. On the other hand, some of 



them are decidedly injurious, and the oystermen 

 complain loudly of the depredations of the "five- 

 finger." If a number of them get on a bed of oysters they will eat many, 

 and hence the fishermen, when they catch one, quickly proceed to cut it 

 up so as to stop the depreciations of one starfish ; but usually their efforts 

 are of no avail, for if but one arm be left attached to the central disc, the 

 others will soon grow out again. The collector at the shore often picks 

 up starfish with one, two, or more rays smaller than the rest, and these 

 smaller arms are records of accidents which the corresponding arms have 

 suffered at some recent time. 



The sea-urchins (Echinoids), though considerably different in shape 

 from the starfish, are somewhat closely related to them. The typical 

 sea-urchin is nearly spherical in form, and yet we can trace the same 

 structures in it as in the five-finger. In a specimen from which the 

 spines have been removed, there will be seen rows of dots running from 

 one pole to the other. These indicate the openings through which the 



just beginning to form: m, 

 mouth; a, vent ; 1 to 5, paired; 

 6, unpaired arm. 



