ACALEPH^;. 211 



the larger animals ; and an animal which we cut and turn inside out, 

 which we cut again, and it still bears itself well, gives one a singular 

 shock. How many facts are ignored, which will come one day to 

 derange our ideas of subjects which we think we understand ! At 

 present we just know enough to be aware that we should be surprised 

 at nothing." 



Notwithstanding the philosophic serenity which Bennet recom- 

 mends, the fact of new individuals resulting from dividing these 

 fresh-water polyps was always a subject of profound astonishment, and 

 of never-ending meditation. 



SERTULARIAD.E. 



All Hydraidse, with the exception of the Hydra and a few other 

 genera, are marine productions, varying from a few lines to upwards 

 of a foot in height, attaching themselves to rocks, shells, seaweeds, 

 and corallines, and to various species of shell-fish. Many of them 

 attach themselves indiscriminately to the nearest object, but others 

 show a decided preference. Thuiaria thrya attaches itself to old bi- 

 valves ; Thoa halecuia prefers the larger univalves ; Antennularia 

 antennina attaches itself to coarse sand on rocks ; Laomedea geni- 

 culata delights in the broad frond of the tangle ; Plumularia catherina 

 attaches itself in deep water to old shells, corallines, and ascidians, 

 growing in a manner calculated to puzzle the naturalist, as it did 

 Crabbe, the poet, who writes of it : 



" Involved in sea-wrack, here you find a race 

 Which science, doubting, knows not where to place; 

 On shell or stone is dropp'd the embryo seed, 

 And quickly vegetates a vital breed." 



Sertularia pumila, on the other hand, loves the commoner and coarser 

 wracks. " The choice," says Dr. Johnston, " may in part be dependent 

 on their habits, for such as are destined to live in shallow water, or on 

 a shore exposed by the reflux of every tide, are, in general, vegetable 

 parasites ; while the species which spring up in deep seas must select 

 between rocks, corallines, or shells." There seems to be a selection 

 even as to the position on the rocks. According to Lamouroux, some 

 polyps always occupy the southern slopes, and never that towards 

 the east, west, or north ; others, on the contrary, grow only on these 



p 2 



