6 FARM ANIMALS 
accumulate the shell is formed. Examples of this group 
are the snails, slugs, mussels and scallops. 
9. Starfish and sea urchin.—These beautiful creatures 
have prickles on their horny 
skins. Sea urchins are some- 
times called ‘‘sea hedgehogs” 
because armed in this way. 
The prickles attain their maxi- 
mum in the sea urchin, but they 
are well represented in the star- 
fish. In the sea cucumber, also a representative of this 
group, the shelly needles are greatly reduced. 
10. Backbone animals.—Scientific men speak of ani- 
mals as either having or not having backbones. Hence, 
animals are called Vertebrata or Invertebrata. Careful study 
has disclosed the fact that all animals are related. The 
higher forms are linked by gradual steps back to lower 
forms. There is no aristocracy in creation. Backbone ani- 
mals from the standpoint of origin have come up out of the 
ranks of the common people of the animal world. No 
longer are the family secrets of 
the higher forms to be kept 
hidden in the locked closets of 
ignorance, 
SNAIL WITH SHELL 
The creatures that connect the 
backbone animals with the family 
lines without a backbone are known 
as -(scidians, or the Chordata. They 
possess a structure called the Noto- 
chord, or a rod down the back. This 
rod is like the cord that precedes the 
backbone in the vertebrate embryo. 
The higher forms of Ascidians attach STARFISH 
themselves without any sensible form 
of support. They possess all the organs of life that the higher water 
forms possess. Their gills are highly developed and contain a spe- 
cial cavity or chamber into which the sea water they breathe is 
passed. 
