406 E. HERON-ALLEN AND A. EARLAND 



builder, and displays the highest development of selective power 

 in the choice of its material. There is, however, a considerable 

 range of skill shown, even among the few species (so called — for 

 specific value is a matter of speculation — or convenience — in the 

 foi aminifera) of this genus, and TechnitcUa thompsoni must 

 unquestionably take first rank for selective power and neatness 

 of construction. Technitella melo (Norman), which favours sponge 

 spicules as building material, is equally skilful at the work of 

 selecting them from the ooze, and builds a neat flask -shaped test, 

 but it employs a considerable amount of ferruginous cement in 

 building the spicules together. Lower still in the scale comes 

 Technitella legumen (Norman), which felts minute sponge spicules 

 and mud together, and builds a pretty and thin-walled flask ; 

 while at the bottom of the scale comes Technitella raphanus 

 (Brady), which, according to the " Challenger " figures, is some- 

 what roughly constructed. 



As illustrating the skill of Technitella thompsoni and the great 

 selective power exhibited by the animal, it may be stated that 

 in neither of the clredgings in which it has been found do 

 echinoderm plates, such as are used in its construction, abound. 

 They occur in considerable numbers, as always is the case in 

 shallow-water dredgings, but they form an infinitesimal percentage 

 of the material as dredged, and their presence would be almost 

 unobserved unless especially searched for. 



We have stated that, in the species above recorded, the power 

 of selection has reached its highest development, as at present 

 observed. It remains for us to note some of the stages by which 

 that development is reached. 



The selective power shown by the arenaceous foraminifera is 

 one of the most striking features of the group. A good deal has 

 been written on the subject, but so far as we know, no explana- 

 tion has been, or is likely to be found. The solution possibly 

 lies hidden in the debatable domain of bio-chemistry, and many 

 of the remarkable experiments of Biitschli with "foams" point in 

 this direction. Meanwhile, it will not be inappropriate to set 

 forth, in connection with the highly specialised test that we 

 have been considering, some of the more prominent examples, 

 and to speculate on the advantages derived by the organism from 

 its selective powers, and which have led to their evolution or 

 development. 



Properly to appreciate the significance of such a marvel of 

 construction as is presented by the shell of any arenaceous 



