FORAMINIFERA 137 



of this group that have not this power, but, instead, 

 lay hold on particles of sand and fragments of shells, 

 spicules, diatom cases in fact, anything that is 

 adapted for building purposes, and with these they 

 are able to make splendid homes or cases. In pond 

 water the ' caddis ' resorts to a similar method. 



This particular class of Foraminifera is splendidly 

 figured and described in Brady's monograph, which 

 forms one of the Challenger Reports. The shells or 

 coverings so constructed are beautiful, both as regards 

 the selection of materials and in the designs embraced. 

 As the materials are not secreted by the Foraminifera 

 of this class, the shells are said to be extrinsic, as 

 instanced in the fresh-water rhizopods. Thus we see 

 some points of resemblance between the microscopic 

 organisms of sea water and those of fresh water. It 

 follows, too, that the nature of the shells, if extrinsic 

 (ie. made up of materials found on the ocean floor, 

 such as particles of sand, etc. 3 as already stated), must 

 entirely depend upon the nature of the remains 

 scattered on the bed of the ocean. Hence, as these 

 materials are very varied, the shells themselves are 

 varied in texture and colour. And as all these 

 creatures have not equal powers, the shapes of their 

 shells are greatly varied. 



One could spend hours looking at the illustrations 

 alone of these marvellous Foraminifera in the work 

 just mentioned. But the objects themselves are 

 much more enchanting, as must always be the case in 

 depicting forms of microscopic life. 



