408 E. HERON-ALLEN AND A. EARLAND 



other hand, chooses fine sand-grains only, of practically uniform 

 size, to build its thick but crumbling wall, in which the sand- 

 grains are held together with a minimum allowance of cement. 

 Psammosphaera fasca (Schulze) takes sand-grains or other fora- 

 minifera without discrimination as to size, and builds a test 

 which no doubt starts with the intention of being spherical, but 

 owing to the irregularity in the size of its constituent fragments, 

 is more often polygonal, or entirely amorphous. It is one of 

 the commonest of the North Sea foraminifera, and, as a builder, 

 probably ranks lowest in the scale. Saccammina sphaerica 

 (M. Sars), on the other hand, using large sand-grains, manages 

 to build a neatly spherical test, often reaching in the North 

 Sea to a diameter of g inch, any irregularities in the shape of 

 the grains being dexterously concealed by turning the irregular 

 surface towards the interior of the sphere, which is as rough as 

 the exterior is neat. Crithionina pisum (Goes), building a spherical 

 test of about the same size, with no distinctive aperture, rejects 

 all sand-grains, and builds a thick wall with the finest mud only. 

 Technitella legumen (Norman), using the same fine mud, felts 

 together a mass of small sponge spicules, and builds a thin- walled 

 flask. Now it is evident that a wall of corresponding thickness, 

 built of mud only, would possess hardly any strength, and it 

 is not unreasonable to suppose that Technitella or its ancestors 

 have found out the advantage to be derived from a judicious 

 mixture of mud and spicules. Teclinitella melo (Norman), of 

 which rare form the same dredging furnished a single specimen, 

 discards mud entirely and cements the sponge spicules together, 

 side by side, with ferruginous cement, exercising great ingenuity 

 in the selection of spicules, or fragments of such, of the correct 

 length for the position required. 



The list might be largely extended, but sufficient has been 

 said to show that the character of the test and the method 

 of its construction are more or less fixed properties inherent 

 in the animal, and that there is as wide a range of " skill ' : 

 displayed by the foraminifera both in choice of material and 

 in actual construction, as by builders in the higher scales of life, 

 not even excepting man. 



Sponge spicules, which abound to a greater or less extent 

 in most deep-sea dredgings, are largely made use of by the 

 arenaceous foraminifera in the construction of their tests, and 

 they are used in an interesting variety of different ways, of 

 which the principal are as follows : 



