556 



THE LOWEST ANIMALS. 



apertures. The seedlet 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 Ch-bitolites 

 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 



