78 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



uous organisms like the majority of those already described. 

 The P oraminifera, on the other hand, are Monera of the 

 Protogenes type, which, nevertheless, play and have played an 

 important part in the history of the globe, by reason of their 

 power of fabricating skeletons or shells, which may be com- 

 posed of horny (chitinous ?) matter, or of carbonate of lime, 

 secreted from the water in which they live, or may be fabri- 

 ated by sticking together extraneous matter, such as par- 

 ticles of sand. 



The first step from such an organism as Protogenes to the 

 Foraminifera is seen in Lieberkuhnia of Claparede, where 

 the pseudopodia are given off from only a small part of the 

 surface of the body, the rest remaining naked and flexible. 



In Gromia there is a similar restriction of the area from 



Fig. 2.— A Rotalia, with extended pseudopodia ; with an enlarged sectional view of the 



chambered skeleton (after Schulze). 



which pseudopodia proceed, but the rest of the body is in- 

 vested by a case of a membranous substance. Let this case 

 become hardened by the attachment of foreign bodies — as 

 particles of sand, or fragments of shelly matter, as in the so- 

 called arenaceous Foraminifera — or let a deposit of calca- 

 reous salts take place in it, and the Gromia would be con- 

 verted into a Foraminifer. 



The infinitely diversified characters of the skeleton of the 

 Foraminifera depend — firstly, upon the structure of the skele- 

 tal substance itself ; and, secondly, upon the form of the pro- 

 toplasmic body, which last, again, is largely dependent upon 

 the manner in which successive buds of protoplasm are devel- 

 oped from the parent mass, which, to begin with, is always 

 simple in form and commonly globular. 



The substance of the calcareous skeleton itself, whatever 



