STANFOR

THE FORAMINIFERA

CHAPTER I

LIBRA

INTRODUCTORY REMARKS ON THE NATURE AND OCCURRENCE OF FORAMINIFERA-IMPORTANCE OF THEIR STUDY TO THE ZOOLOGIST AND GEOLOGIST-THE STRUCTURE AND CLASSIFICATION OF THE PROTOZOA-THE POSITION OF THE FORAMINIFERA IN THE PHYLUM PROTOZOA.

Where to find Living Foraminifera.-The most casual observer who takes a walk by the seashore, especially if it be in a sheltered bay with a gently sloping strand, will have noticed the sandy streaks left by the receding tide. If this sand, which to the eye appears like a collection of mere chalky and sooty fragments, be examined with a pocket lens, some of the whitish specks will be seen to be tiny but perfect shells. These delicate little shells belong to the lowest group or phylum of animal life, and they are known as Foraminifera, 'hole-bearers,' as the name implies, on account of their internal septa having perforations.

There may be other little organisms accompanying the Foraminifera in this sand, such as the shells or carapaces of bivalved crustaceans or Ostracoda, the young shells or fry of molluscs, or even seeds of

The shells of the Fincidifers are easily distinguished by their particdr die ui texture: they are sometimes wite and cpayne, classy or mansiolent, and then beamed at the frog and most beautiful fice takery. Their minuteness. evenly do i stresk may be conceived So the fact that the observer. Plinius conted ARe of sand of sand for the Vida. This I

perhaps rather within than begin the

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See Frontispiece.

Flo. I represents a simple of seressen 1 from the

sands, however, may not contain the living animal, since they have probably drifted and floated on the tide for some length of time.

The shallow-water sands of the Grecian Archipelago and the Levant often contain a large proportion of foraminiferal shells; and by taking a common washing sponge, obtained from such a locality, in the dry state before it has been used, and shaking it over a sheet of paper, we may obtain a quantity of fine

sand which, on examination with a lens or low-power microscope, will often reveal countless shells of the Foraminifera (fig. 2).

In order to see these tiny creatures alive let us take some fresh seaweed at low tide and place it in a glass jar of sea-water. After a After a short space of time the Foraminifera will be seen moving over the inside of the vessel, whither they have travelled from the

seaweed, and they can then be observed with a moderately powerful lens.

Living Foraminifera are very beautiful objects when viewed by means of a back-ground illumination, using an objective of about 40 diameters. The shell under these conditions appears surrounded by a sort of cobweb of extremely fine sarcode threads, which, if observed closely, will be seen to exhibit a streaming

WITH

× 72. After Schultze.

movement, owing to the rapid circulation of crystalline particles in the sarcode, reminding one of the cyclosis or circulatory movements seen in the cells of certain plants. A reproduction of Schultze's figure of a living Haplophragmium, given above, affords a good idea of the appearance of the living organism (fig. 3).

How to find Fossil Foraminifera. Fossil specimens may also be obtained with very little difficulty;

as, for example, by crushing a piece of soft white chalk under water, and repeatedly washing the residue, taking care that nothing but the fine milky fluid is thrown away during the process of levigation. After drying the residue, the powder thus obtained will probably yield numerous specimens of Foraminifera. That some chalks and limestones are largely composed of foraminiferal shells we may see by examining

× 36.

Original.

thin slices of these rocks from certain horizons. Fig. 4 is taken from a photomicrograph of a section of the chalk-rock of Buckinghamshire; in this zone the Foraminifera are always abundant. The separated microzoa often contain some handsome forms, as the next illustration (fig. 5) will show. To be successful, however, in extracting Foraminifera from the chalk, it must be borne in mind that some strata are almost