268 THE MICROSCOPE. 



and under different modes of illumination and of pre- 

 paration, in order to arrive at a due conception of their 

 astonishing conformation. 



When the shells of Foraminifera are dissolved 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 consti- 

 tuent 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 Polystomella strigilata from the 

 Adriatic. 



Fig. 164. 



J, Separated prisms from outer layer of Pinna shell. 2, Skeletons of Forami- 

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

 the dark-ground illuminator. 



The solitary BMzopoda, 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 

 Englypha it is of an oval or flask-like form, with the 



