WORMS 63 
forms of sea-lilies can be traced back as far as 
Cambrian rocks. The extinct Cystideans (Greek, 
kystis=a bladder), fossils of which have been dis- 
covered in marine deposits of Cambrian and'Silurian 
Ages, may have been early an- 
cestors of the crinoids. They 
had rounded or oval, bladder- 
like bodies, enclosed in plates 
of lime, with just the beginnings 
of arms and short jointed stalks. 
Higher still in the scale‘ of 
life-forms we have the fifth great 
subdivision, the Vermus (Latin, 
Hxtracrinus Briareus (Jurassic). Periechocrinus monilt- 
formis (Silurian). 
Fig. 13.—Fosstn S#a-LiIt1es oR CRINOIDS. 
vermis =a worm). Worms are more highly developed 
creatures than any we have yet considered. ‘They 
possess jointed bodies and nervous systems; they 
also have an internal digestive canal and a number 
of organs. Few of the worms are found in a fossil 
