280 SECRETS OF ANIMAL LIFE 



transformation (if any) is invisible; all that we do 

 observe is the rising of a visible and tangible edifice 

 in the transparent medium of the Foraminifer's 

 protoplasm. But the arenaceous forms use visible 

 ready-made building materials, and make of them 

 an encasement. This is sometimes beautiful, oftener 

 perhaps simply quaint; the interest centers in the 

 selection of the materials and in the effective 

 architecture. First as to selection: a particular 

 kind of Foraminifer surrounded by an embarrassing 

 wealth of alternatives will have none of them save 

 intact sponge-spicules, out of which a transparent 

 test is built up. Another kind will use only grains 

 of quartz, and a third flakes of mica. What ex- 

 periment will show is whether this particulate 

 utilization of certain materials is obligatory or facul- 

 tative? Is past experience so enregistered within 

 the cell that the searching living threads will respond 

 to sponge-spicule only ? Or would the creature take 

 Echinoderm fragments in default of anything 

 else? Quite extraordinary is the case of a species 

 of Technitella which makes its test of Echinoderm 

 plates, and, having no definite oral aperture, 

 sends its living threads flowing through the pores 

 which these plates possess. How interesting, too, 

 is the morsel of fact that one type that makes 

 a shell of sponge-spicules will only use them 

 intact, while another type will only use them 

 broken! It has been suggested that when the 

 materials used by a particular type are all of the 

 same kind, and therefore of the same specific 



