SPONGES, ZOOPHYTES, AND SEA-FIRS. 51 



may be briefly described, as they are so common that almost 

 every patch of rocks will furnish examples. If at an ex- 

 ceptionally low tide you make your 

 way right out to the margin of the 

 rocks, where the great oar -weed 

 spreads its long fronds, or if a calm 

 summer day permits the slightly 

 dangerous experiment of a boat 

 among the rocks, you will notice that 

 the oar-weed is often covered by a 

 miniature forest of sea-firs. Especi- FIG. w.OMia genicuiata on 



.,, ,. , . , r weed. After Hmcks. 



ally will you notice one which con- 

 sists of slender zigzag stems, giving off stalked cups bear- 

 ing tiny crystalline specks the expanded zooids. This is 

 Obelia genicuiata^ seen at its best only thus in the Lami- 

 narian zone, but in the dead state common enough at all 

 seasons on the torn-off weed of the beach. It gives 

 rise in the summer months to countless myriads of 

 tiny swimming - bells, which are liberated from little 

 cases, or gonothecse, borne on the stems. If myriads seem 

 to you an exaggeration, take a few patches of the sea-fir 

 and make a rough computation even of the gonothecse pro- 

 duced by a patch of ordinary size: If your patience does 

 not speedily give out, you may acquire some perception of 

 the prodigal profusion of nature on the seashore, and of 

 the intensity of the "struggle for existence" which must 

 go on there, where so many species produce eggs numbered 

 in millions. 



Another common Campanularian Clytiajohnstoni is to 

 be found on almost every object within the shore area 

 which offers a foothold shells, weeds, stones, rock surfaces, 

 are eagerly taken possession of, but the back of a spider-crab 

 is also a dearly prized position. Almost any spider-crab 

 taken at random will show you the simple unbranched 

 stalks of Clytia, each ending in a solitary bell, but you 

 should also look for it on rock surfaces, as a good means of 

 training the eye. It is by no means a conspicuous object. 



Let us mention one other common Campanularian which 

 is also to be found everywhere between tide-marks. This is 

 Campanularia flexuosa, which often grows, intermixed 

 with weed, in patches of great extent, and can be recognised 



