Bfyozoans 



167 



nies are often large and conspicuous. Two of the 

 commoner genefsi, ' are shown in figure 76, riatural 

 size. These may be found in every brook or pond, 

 growing in fiat spreading colonies on leaves or pieces of 

 bark or stones. Often a fiat board that has long been 

 floating on the water, if overturned, will show a com- 

 plete and beautiful tracery of entire colonies outspread 

 upon the surface. New zooids are produced by bud- 

 ding. The buds remain permanently attached, each 

 at the tip of a branch. With growth in length and the 

 formation of a tough brown- 

 ish cuticle over every por- 

 tion except the ends, the 

 skeleton of the colony devel- 

 ops. This skeleton is what 

 we see when we lift the leaf 

 from the water and look at 

 the colony — ^brown, branch- 

 ing tubes, with a hole in the 

 end of each branch. Noth- 

 ing that looks like an ani- 

 mal is visible, for the zooids 

 which are very sensitive and 

 very delicate have all with- 

 drawn into shelter. They 

 suddenly disappear on the slightest disturbance of the 

 water, and only slowly extend again. 



If we put a leaf or stone bearing a small colony into a 

 glass of water and let it stand quietly for a time the 

 zooids will slowly extend themselves, each unfolding a 

 beautiful crown of tentacles. There are few more 

 beautiful sights to be witnessed through a lens than the 

 blossoming out of these delicate transparent, flower- 

 like, crowns of tentacles from the tips of the apparently 

 lifeless branches of a populus colony. They unfold 

 from each bud, like a whorl of slender petals and slowly 



Fig. 77. Three zooids of the bryo- 

 zoan, Plumatella, magnified. 



I, expanded; m, retracted; «, partly re- 

 tracted; », anus; j, intestine; ft, de- 

 veloping statoblast. 



