i 7 8 



THE BOOK OF NATURE STUDY 



We have referred to a few animals to be seen near the high- 

 water mark, but let us suppose that we have got down to a more 

 typical level. What should we look for on a first excursion ? 



Coating the rocks, especially under ledges, is the crumb-of- 

 bread sponge (Halichondria panicea), very varied in its thickness 

 and vigour of growth, with numerous exhalant orifices like the 

 craters of volcanoes. It is interesting to find a 

 piece on a loose stone or on a detachable corner, 

 to put this uninjured into a bowl of water, to 

 add a little powdered carmine, and thus to 

 verify the fundamental fact that the water passes 



in by minute pores all 

 over the surface and 

 passes out by the large 



A B 



FlG. 93. Zoophytes thrown up on the shore (natural size). A, Bottle brush coralline 

 (Jlhuiaria thuja] ; B, Hydrallmaniafalcata ; C, Sea-fir (Sertularia abietina). 



apertures. These currents depend on the internal activity of 

 thousands of lashed cells, something like those which keep our 

 windpipe clear, and on these currents the whole life of the sponge 

 depends, for the water brings in food particles and oxygen and 

 sweeps out waste. If the body of an animal be compared to a city, 

 the body of a sponge may be compared to Venice. We should 

 look for the calcareous purse sponge (Sycon compressutri), and 

 inquire why it can live farther up the shore than its near relative 

 Sycon ciliatum. Very common are still smaller and simpler 

 calcareous sponges delicate white tubes such as Leucosolenia 





