CHALK MAKERS, OR FORAMINIFERA. 33 



Without staying here to pursue further inquiries 

 as to the structure and habits of the naked Amcebcz, 

 we may pass to the simplest condition of an Amoeba- 

 like body enclosed within a shell, or house, which it 

 constructs for itself by accumulating grains of sand 

 and other foreign particles which adhere to the 

 membraneous covering of the animal. The species 

 of Difflugia are also found in 

 fresh water, and are rather com- 

 mon, but not being considered 

 generally attractive, are but little 

 studied (fig. 2). The coat, or 

 " test," is usually ovoid, or flask- 

 shaped, with a notched aperture FIG. 2. DIFFLUGIA.. 

 at the end, its foundation is a 

 thin transparent colourless membrane, and to tln 

 the particles adhere to form the encrusted house ii 

 which the animal dwells ; the pseudopodia arc 

 protruded from the orifice only. 



The transition is a short and easy one to the 

 Foraminifera, those minute marine animals of very 

 near kindred to Amceba, who construct for themselves 

 a calcareous shell, or skeleton, many of which in form 

 resemble very microscopical snail shells. (Plate I.) 

 From the perforations which the walls of these shells 

 present they were called Foraminifera^ or pore-bearers 

 and though small, they are, or have been, probably 

 the most numerous of all created things, and have 

 I) 



