FORAMINIFERA. 375 



Dr. Schultze acknowledges the difficulties attending the 

 study of the Rhizopoda, and insists, very properly, upon 

 the necessity of viewing them in all positions, and under 

 different modes of illumination and of preparation, in 

 order to arrive at a due conception of their astonishing 

 conformation. When the shells of Foraminifera are dis- 

 solved in dilute acid, an organic basis is always left after 

 the removal of the calcareous matter, accurately retaining 

 the form of the shell with all its openings and pores. 

 The earthy constituent is mainly carbonate of lime \ but 

 Dr. Schultze has satisfied himself of the presence of a 

 minute amount of phosphate of lime in the shells of 

 recent Orbiculina adunca from the Antilles and of Poly- 

 stomdla strigilata from the Adriatic. 



Fig. 207. 



1, Separated prisum From outer layer of Pinna shell. ^.-Skeletons of Forami- 

 nifera from limestone. 3, Recent shell of Polystomella crlspa; viewed with 

 dark-ground illuminator. 



The solitary Rhizopoda, furnished with a horny shell or 

 capsule, forming a case for the animal, is nearly the only 

 representative of the Arcellidce. In the Arcella, from 

 which the family derives its name, the shell is somewhat 

 of a bell-shape, with a very large round opening. In 



