124 CCELENTERATA OR STINGING-ANIMALS. 



fishes which throb in the tide and are often cast in large 

 numbers upon the beach, but the step is greater than it 

 seems. Like as they are in habit, these two sets of animals 

 are separated by marked anatomical differences. They 

 form two independent series. Yet in a way they are 

 parallel, for here again we find one type {Pelagia) always 

 locomotor, another (Aurelia) whose early life is sedfentary, 

 and others (Lucernarians) which in their adult life are 

 predominantly passive, mooring themselves by a stalk. 



The Lucernarian jellyfish, and the sedentary juvenile stage 

 of the common Aurelia, a.Te of great interest, because they 

 seem to point the way to the sea-anemones. These are 

 sedentary polypes like the Hydra, but of much greater com- 

 plexity, and with certain peculiarities of structure which 

 suggest the alliance mentioned above. We may think of a 

 medusoid as an inflated hydroid polype adapted for swim- 

 ming, and there is a somewhat similar but vaguer relation 

 between jellyfish and sea-anemone. And again, just as there 

 are colonies of polypes of the Hydra type, so there are 

 colonies of polypes belonging to the sea-anemone type, not- 

 ably many corals and also dead-men's-fingers {Alcyonium 

 digitatum), which is common in deep water around our coasts. 



It is well to note explicitly that various polypoid types 

 may form corals. In fact we may directly associate their 

 sedentary passivity with the formation of a framework of 

 carbonate of lime. Shells of lime are naturally connected 

 with lazy life, (i) There are (Zoantharian) corals of the 

 strictly sea-anemone type — madrepores, brain-corals (Mcsan- 

 drina), and star-corals {Astrcea), all important in the build- 

 ing of reefs. (2) Then there are other (Alcyonarian) corals 

 whose polypes are like those of dead-men's-fingers — the 

 "noble coral" of commerce {Corallium rubrum) with its 

 solid red axis around which the individuals are clustered, 

 the organ-pipe coral (Tubipora musica) in which the spicules 

 are fused into external tubes, the blue coral {Heliopora 

 caruled), and many known as Gorgonids with flexible axes. 

 (3) Again, there are other (Millepore) corals of the 

 hydroid type, in which seven or eight small tactile " per- 

 sons" are grouped in calcareous tubes round a larger 

 nutritive " person," a series of which Distichopora is a well- 

 known representative. Did space permit I should like to 



