Flowerlike Forms and Fantasies 173 



and their branches are so fine as sometimes to be almost 

 invisible. When magnified, a branch will be found to 

 consist of a horny shell or tube divided into more or 

 less regular internodes. In some species this tubular 

 branch contains a single canal throughout its length; in 

 others, it may contain several. These canals contain 

 living substance, the horny exterior being only a sup- 

 port and protection. But the most striking thing that 

 greets the eye are the flowerlike forms arranged alter- 

 nately along opposite sides of the internodes, and which 

 constitute the individual animals themselves. Each one 

 is an anemonelike creature — in this case, called the 

 hydranth — held in a transparent cup of amber, over 

 the brim of which it spreads a spray of sixteen tentacles, 

 silvery petallike processes of gossamer fineness. These 

 are arranged in a single whorl around a conical, or 

 dome-shaped, proboscis having in its center a tiny aper- 

 ture, the mouth. The cup that holds the hydranth is 

 known as the hydrotheca, and in sertularians this is 

 almost always set close to its supporting branch without 

 a connecting stem, or pedicel. On the hydrothecal rim 

 is a hinged structure which works like a trapdoor when 

 the hydranth retracts, closing after the animal to pro- 

 tect it from harm. A diaphragm forms the floor of the 

 cup, and through a hole in this passes part of the body 

 of the hydranth, making it continuous wMth the other 

 hundreds of hydranths which compose the colony. 



At occasional points along the branches, larger urn- 

 shaped bodies are to be seen. These are the repro- 

 ductive organs {gonosomes) , and with rare exceptions 

 the entire colony will contain sex organs of one kind 

 only — which is to say, the colony is either male or 



