THE MOSS ANIMALS AND CORALLINES 



Polyzoa or Bryozoa. 



\ MOMENT'S glance at a bit of seaweed or the most casual in- 



spection of the rocks below low tide level, will reveal the fact 

 they are often covered with delicate lace-like growths, or with more 

 or less highly colored incrustations, or small tree-like forms. 



These are the moss animals or corallines. They live in col- 

 onies, and grow by budding, the entire colony having grown 

 from a single individual, and thus while the individual creatures 

 are themselves of microscopic size, the colony being composed of 

 liundreds or thousands may spread over a considerable area or con- 

 stitute a small tree-like, or moss-like, growth. 



Each little animal of the colony occupies a separate stony or 

 horny capsule into which it may withdraw and even close the 

 opening with a lid, the aperture being still further protected by 

 spines around its edge. 



The mouth is surrounded by tentacles that in many s])ecies 

 arise from a horseshoe-shaped or disk-like base. These tentacles 

 are always beset with hair-like bristles which h\ their movements 

 serve to set up currents, and thus to drive minute organisms into 

 the mouth. 



The intestine is U-shaped and bends back so as to open on the 

 dorsal side near the mouth, while the principal nerve centre is situ- 

 ated between the mouth and the vent. In some of the forms there 

 is a single pair of kidney organs, the ducts of which open near the 

 mouth. 



We see, therefore, that although these creatures often bear a 

 close superficial resemblance to hydroids they can at once be dis- 

 tinguished by their bristled tentacles and complete alimentary tract. 

 Indeed a careful study of their development and anatomy has shown 

 that they are closely related to the brachiopods and worms, and that 

 their present forms have been brought about by ages of sedentary 

 life. Being stationary they have had little need for sense organs. 



