Bryozoans 



i6 7 



nies are often large and conspicuous. Two of the 

 commoner genera are shown in figure 76, natural 

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

 growing in flat spreading colonies on leaves or pieces of 

 bark or stones. Often a flat 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 populous 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; n, partly re- 

 tracted; t, anus; j, intestine; &, de- 

 veloping statoblast. 



