THE YOUNG NATURALIST. 



59 



EXCHANGES. 



Duplicates. — Dealbata, Candidate, Gemina, 

 'ulvago, Triangulum. Brunnea, Festiva, Doaonea, 

 )ominula, Truncicolella, Inquinatellus, &c. W. 

 'riest, 13, Holgate-road, York. 



STARFISHES & SEA URCHINS. 



ABSTRACT OF A LECTURE 



By George Brook, ter, Esq., FL S. 



^hese two kinds of animals belong to a class 

 ailed Echinodermata. In the Sea Urchins, the 



Fig. 30. — Sea Uurchin, w'th spines partly 

 removed. 



nimal secretes a calcareous (limy) .shell, which 

 overs the living part. This shell is covered on 

 le outside by little granules of the same substance 

 nd outside all are numerous spines which the 

 nimal can move about at will. Inside the shell 

 lere is a series of vessels, through which water 

 ows, called the "water vascular system," and 

 lese work a sort of tube-feet which open through 

 ie shell, and are capable of being pushed out be- 

 3nd the spine. It is by means of this system that 

 "comotion is effected. The mouth is underneath, 

 id situated in the centre, as is apparent on turn- 

 ig one up. These animals, like Star Fishes, are 

 iade up of five parts or rays, though sometimes — 

 Jt rarely — of ten, or more. If you examine a 

 ea Urchin's shell, you will see that it is made up 

 f five divisions, each one having its own set of 

 rgans inside, but not independent of each other, 

 hey have no respiratory system. Their young 



are very different from the adult forms, and might- 

 be taken for totally different animals. Star Fishes 



Fig. 31. — Star Fish, upper side. 



do not secrete a calcareous shell ; they are usually 

 composed of five rays, (very rarely of four or six) 

 or a multiple of five. These animals perform 

 locomotion by means of tube-feet — which are 

 themselves moved by means of the water vascular 

 system — as in the Sea Urchins. The mouth is 

 underneath and in the centre, from which spring 

 the various organs of the body. If you cut off one 

 of the rays of a Star Fish, a new ray will be 

 developed, and the limb will often grow into a 

 perfect animal. The Brittle Stars are similar, but 



Fig. 32.— Brittle Star. 



the arms long and slender, and the body part very 

 small. They differ from the Star Fishes in having 

 a distinct point of attachment of each arm to the 



