SERTULARIA — PLUMULARIA. 117 



creature, or rather of this creature-mass, is very 

 interesting, and worth studying practically. 



On plate b, fig. 1, is shown an example of a 

 plant-like, compound animal, very common on 

 the coasts, either thrown on the shore dead or 

 dying, or affixed to large algae, near low water- 

 mark. This is the Sertularia, a beautiful family 

 of zoophytes, of which some sixteen or seventeen 

 species are found on our own coasts. The species 

 represented is perhaps the commonest of all, 

 Sertularia filicula. 



If one of these creatures is examined by the 

 aid of a moderately powerful lens, it will be seen 

 to consist of a horny, many-branched stem, each 

 branch being studded with a double row of little 

 cells, open at the mouth, which is much smaller 

 than the base. If the creature is placed in clear 

 sea-water, and still watched through the lens, 

 each cell will be seen to protrude a tiny polyp, 

 whose star-like head is all that is visible ex- 

 ternally. The polyps are easily alarmed, and 

 in such a case withdraw themselves wholly 

 within their cells. There is a very similar 

 zoophyte called by the name of Plumularia, 

 which may, however, be easily distinguished 

 from Sertularia, by the position of the polyp 

 cells, which only occupy one side of the branches j 



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