556 
THE LOWEST ANIMALS. 
apertures. The seecllet miliolina, previously referred to, is one of the commonest 
species ; it has a world-wide distribution from the shore to three thousand fathoms. 
The terminal opening of the last and largest segment is guarded by a branched 
tongue-like process. The Miliolite Limestone of the Paris 
Basin is composed almost entirely of the shells of Miliolina 
and other Foraminifera. A considerable part of Paris is 
built of this stone, in which the tiny miliolinas can be 
distinctly seen with the aid of a lens. The porcellaneous 
Peneroplis forms a spiral, with a slit in the last-formed 
segment, through which the protoplasm of the body can 
be extruded. 
Orbitolites, one of the Imperforata, forms discs from 
one to two inches in diameter. The shell is composed 
of a central coiled chamber, followed by concentric circles 
of chambers, the pores for the emission of pseudopods 
being situated on the edge of the disc. The different 
species of Orbitolites form an interesting series, illustrat¬ 
ing transitions from a simple to the most complex type. In a vertical section 
of the disc of the figured species the innermost chambers exhibit the simple type, 
later formed ones the intermediate, and the outermost series the highest type and 
the greatest differentiation of structure. 
Peneroplis pertusus. a, Lateral 
view ; b, Front view. (Mag¬ 
nified.) 
Orbitolites. a, From above ; b, Transverse section (nat. size); c, Diagrammatic figure of section of Orbitolites 
complanatus, illustrating the transition from the simplest to the most complex type of structure. 
The shells of the perforate Foraminifera may be constructed of only one, 
but most commonly of many, chambers, arranged according to various plans. 
The simplest type with one chamber ( Lagena ) is shaped like a Florence oil- 
flask ; in many-chambered forms the segments may succeed one another in a 
