PROTOZOA — FOEAMINIFEEA. 
17 
are preserved in the rocks. This shell encloses the main Gallery X. 
mass of protoplasm, bnt the pseudopodia stretch out through 
certain openings. Either they are confined to the aperture 
of the shell, or the whole shell-wall is pierced by minute 
tubes through which the protoplasm cau pass (Fig. 1). Shells 
of the first kind are called Imperforate, and maybe chitinous, 
arenaceous, or calcareous. Shells of the second kind are 
called Perforate, and are generally calcareous. The Imper- 
forate calcareous shells are chalky-white and rather like 
porcelain in appearance, whence they are called Porcellanous. 
The Perforate calcareous shells are of more glassy'' appearance, 
and are therefore called Hyaline. Both types of calcareous 
shell are made of calcite, but in porcellanous shells this is 
less pure. Attempts to classity Foraminifera according to 
the composition of the shell have not proved satisfactory, 
since genera or species which in other respects appear closely’’ 
allied differ in this respect. 
The form of the shell varies greatly'. It may be simply 
flask-shaped, without divisions, e.g. Lagena (Fig. 3 /) ; or the 
animal may grow out of the opening of such a single 
chamber and fashion for itself another chamber adjoining 
the first, and as it grows it may' build chamber after chamber 
(Fig. 2 a). Shells of the former type have been called 
Fig. 2. — A Foraminifer from the Upper Chalk, Anomalina atnmonoides. 
a, the shell ; b, flint cast of the chambers of a similar shell, showing the 
form of the protoplasmic body. Highly magnified. (From Chapman’s 
“ Foraminifera,” after Eley. By permission of Messrs. Longmans.) 
IMonothalamia (single-chambered), those of the latter type, 
Polythalamia (many-chambered). A hundred years ago, 
c 
