358 



THE MICROSCOPE. 



Linnaeus made a large genus of them ; but Lamarck con- 

 siderably reduced his classification. There, are seventeen 

 British species, which Dr, Fleming proposes to divide into 

 two groups, with stems simple or compound. 



The tentacles of Sertularia 

 are abundantly supplied with 

 cilia ; the cells are pitcher- 

 shaped, arranged alternately, 

 or in pairs obliquely, not 

 exactly opposite, on the stem 

 and branches of the polj- 

 pidom, which is horny. La- 

 mouroux classed with this 

 family Thoa; of which there 

 have been several kinds found 

 in Great Britain. The name 

 is supposed to be derived from 

 the Greek word for shar%) ; 

 but we think, with Dr. John- 



mg.l91.-Sertularia,Pol yP idomof. . 



is a mis-spelling of Thoe, one 



of the Nereids, nymphs of the sea. They are generally 

 of a brown and yellow colour, branched, and from an inch 

 and a half to six inches in height. 



Sertularia pumila. This is parasitic, and spreads its 

 brown-coloured shoots over various fuci and sea-shells; 

 but rarely attains more than half an inch in height. 

 Stewart says : " This species, and probably many others, 

 in some particular states of the atmosphere, emits a phos- 

 phorescent light in the dark. If a leaf of the fucus 

 serratus, with Sertularia upon it, receives a smart stroke 

 in the dark, the whole is most beautifully illuminated, 

 every denticle seeming to be on fire." 



On the south-eastern coast of England the most common 

 kind found is the Sertularia setacea, which, after rough 

 weather, is cast on the shore attached to sea-weed. The 

 stem and branches seem composed of separate pieces, 

 fitting into each other as some foreign trees do, and termi- 

 nate in a star-like head, from which radiate the feelers or 

 arms. Dr. Mantell states he was present on one occasion 

 when Mr. Lister was observing a living specimen: a little. 



