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Proceedings of the Royal Physical Society. 



(Browne, 1899); (3) that the specimen has drifted thither 

 from its Australasian locality. 



The twig to which the colonies are attached helps to a 

 conclusion. Cross and longitudinal sections are character- 

 istic, showing a central strand of sclerenchyma surrounded 

 by loose lacunar tissue, which again is surrounded by a thick 

 band of sclerenchyma. The twig and sections were shown 

 to Prof. J. W. H. Trail, M.D., F.RS., to whom I am 

 indebted for kind assistance, and he pronounced the branch- 

 ing and microscopic structures to be those characteristic of 

 the marine phanerogams of the subfamily Cymodoceese in 

 the family Potamogetonacese. This subfamily contains but 

 nine species, all of them, with one exception, belonging to 

 tropical or south temperate seas, the majority occurring in 

 West Indian, Indo-Pacific, and Australian waters (Eagler 

 and Prantl, 1889). The exception, the only north temperate 

 form {Phucagrostis major), occurs in the Mediterranean Sea 

 and along the Spanish and African coasts, but its structures 

 are quite distinct from those of the present specimen, and it 

 may therefore be left out of consideration. If, then, it is 

 assumed that the North Sea Hydroid specimen grew upon 

 the plant in situ, and it is the habit of Sertularia elongata to 

 grow upon seaweeds (vide Bale, Allman, etc.), the twig may 

 be taken as indicating a tropical or south temperate origin 

 for the specimen. 



Since so conspicuous a Hydroid has not been recorded by 

 any of many careful workers, and has not been found in 

 many recent dredgings, from the North Sea, and since it has 

 grown upon an exotic plant, the first supposition, that the 

 species grows in the North Sea, may be rejected. The second 

 supposition is also rendered impossible, because the very fact 

 that the specimens have grown upon a twig excludes the 

 possibility of their having been attached to a ship's bottom 

 and thus transported. The conclusion remains, and it is 

 indicated by the known distribution of Sertularia elongata, 

 as well as by the characters of the twig to which the 

 specimens are attached, that the North Sea specimen has 

 drifted, probably from an Australasian, perhaps from a West 

 Australian, locality to the spot where it was picked up. 



