They present, however, structural differences from Eozoon, which rather conforms to the arrangements found in some Protozoa of smaller size, and which, under the name of Foraminifera, have abounded in all geological periods, and are excessively abundant in the modern ocean. They may be defined as animals composed of a soft and apparently homogeneous animal jelly known as protoplasm or sarcode. When carefully examined, however, it is found to have a granular texture and to be divisible into two layers, an outer and an inner, while it possesses a little hollow vessel capable of expanding and absorbing the liquid matter of the enclosing protoplasm, and of contracting so as to expel its contents. This seems to be the only organ of circulation and excretion. There are, however, small cells or reproductive bodies in the interior, varying in number, size, and development in different forms. The most remarkable property of these creatures is that of stretching out from the surface of the body threads or projections of the protoplasm,[37] often of considerable length, and which serve at once as organs of locomotion and prehension. [Footnote 37: Known as Pseudopodia.] [Illustration: _Amœba._] [Illustration: _Actinophrys._] From original sketches. [Illustration: _Biloculina._ A many-chambered Foraminifer. Magnified as a transparent object.] [Illustration: _Polystomella._ A spiral Foraminifer. Magnified as an opaque object.] Fig. 46.--Recent Protozoa. These creatures are in some respects the simplest of animals, yet in other respects they present strange complexities. This is more especially evident in their tests or coverings, made for the most part of limestone or calcium carbonate, but sometimes of grains of fine sand cemented together. These coverings are always perforated with at least one orifice for the emission of the thread-like processes or pseudopods, and often with a vast number of small pores for the same purpose. Sometimes the test or shell is smooth, sometimes beautifully sculptured externally. Sometimes it consists of a single chamber like a ball or vase. More often, as the animals increase in size, they form additional chambers, and the body thus becomes divided into lobes connected with each other by necks passing through orifices in the partitions. The chambers are arranged in rows or in spirals, and in other ways, giving a vast variety of forms, often presenting the most beautiful patterns executed in the purest white marble, and the ornamental parts constitute thickenings of the walls giving greater strength, and are penetrated with microscopic canals communicating with the soft substance of the animal.