172 Dwellers of the Sea and Shore 



throughout their communal life. That is to say, like 

 plants they spend their entire adult life on the spot 

 where they originally started to grow. It is true, in this 

 respect they do not differ from the sponges, but so much 

 more pronounced is their plantlike appearance that the 

 comparison here is quite to the point. Some there are 

 which liberate swimming bells. It is for this reason 

 that hydroids often have been called the nurses of 

 jellyfishes. 



Throughout the summer months the fixed hydroids 

 are well represented in my tide pool. However, of the 

 four main groups, or genera, into which these animals 

 are divided, tiibularians, campaniilar'ians, sertidarians, 

 and phimidarians, the sertularians are the most abun- 

 dant. Hanging like frosted fringes from the fronds of 

 seaweeds, can be seen the silver sertularian {Scrtularia 

 argentea) \ and the sea cypress {S. cupressina)^ a 

 species somewhat similar, with its arched and drooping 

 branches, forms funereal groves over shells and stones; 

 but the commonest and in one sense the most curious is 

 the creeping sea oak {S. piimilla). This hydroid criss- 

 crosses its silken stems in such profusion that it some- 

 times hides completely the rocks or seaweeds on which 

 it grows. From the tangled w^eb, there rise at close 

 intervals slender, upright stalks about an inch in height 

 adorned with zigzag branches. 



But how is one to determine their animal nature and 

 avoid confusing them with seaweeds, which they so ob- 

 viously simulate? Very easily. A strong glass, how- 

 ever, must be used for the purpose. All hydroids, in 

 fact, can be studied to advantage only under the lens. 

 Few sertularians, as a rule, reach higher than a foot, 



