RHIZOPODA. 17 



prey, adjoining fibres aggregate about it and coalesce, 

 a current of the viscous substance, so to speak, sets 

 in towards the spot, and very soon envelopes the 

 object in a thin film. The prey being thus secured, 

 the glairy cords shorten themselves and draw it 

 towards the chief mass or body of the animal, or 

 else the object seized continues in the same place, 

 and the whole organic substance moves towards it, 

 the result being in either case that it is engulphed 

 and dissolved. 



The size of the Ehizopods is exceedingly minute. 

 Ehrenberg describes Amoeboe, the dimensions of which 

 range from 2 gV^^^i to ij\ih of an inch. The largest 

 fresli water forms only attain a diameter of -^nd 

 part of an inch, whilst the largest marine species, 

 which are just visible to the naked eye, do not measure 

 more than from ^th to -^th of an inch. 



Notwithstanding their minuteness, however, the 

 reader will now begin to perceive that these humble 

 creatures, diffused in countless multitudes through 

 every sea, and cased in shells of such exquisite work- 

 manship, are by no means unimportant agents in the 

 economy of Nature. Their numbers make up for 

 the minuteness of their dimensions, and assiduously 

 employed as they have been from age to age, we are 

 not surprised to find that they, like the vegetable 

 forms described in the last chapter, have been 

 important agents in the construction even of extensive 

 geological strata. 



The extraordinary abundance of foraminiferous shells 

 in the sand of some sea-shores has been long observed ; 

 Plancus, in 1739, counted, with the aid of a low magnifying 

 power, 6,000 individuals in an ounce of sand gathered 

 at Kimini, upon the shores of the Adriatic sea. D'Orbigny 

 states that 3,840,000 exist in an ounce of sand from the 

 Antilles ; and Schultze counted 500 shells in the ^th of 

 a grain of sand collected from the mole of Gaeta on the 

 shores of the Mediterranean, 



Ehrenberg describes finding chambered shells such as 

 we have delineated both on the surface of the sea, and 



