762 GROWTH OF FORAMINIFERA. 



which the filaments can be projected ; while the greater number of the known species 

 are furnished with shells very similar in form to those of the molluscs, and in some cases 

 wonderfully similar to the highly complicated dwelling of one of the highest molluscs 

 the pearly nautilus. 



These minute though beautiful beings exist in numbers that are only rivalled by the 

 sands of the sea for multitude ; and the vast hosts of these creatures can be barely 

 estimated even when we know that many large cities are built wholly of the dead 

 skeletons of these microscopic beings, and that in a single ounce of sand from the 

 Carribean Sea nearly four millions of these shells have been discovered. The living 

 species are not nearly so numerous as the fossil, but even the known species of this class 

 form no inconsiderable addition to the British fauna. They can be captured in various 

 ways. If, for example, growing algae be plucked, and placed in a glass vessel of sea- 

 water, the Rhizopods will leave the algae, and settle on the sides of the vessel. If they 

 live in muddy substances, such as the " oyster-ooze," which is especially prolific in 

 Rhizopod forms, the upper layers of mud should be taken off and stirred up in a vessel 

 of clear sea-water, when the creatures will sink to the bottom of the vessel, and may 

 easily be separated. 



These modes are adopted for living specimens, but if the dead skeletons only are 

 required, they can be procured in many ways. One of the simplest methods of finding 

 Rhizopod shells is, to shake the dust out of sponges, and to examine it when laid thinly 

 on black paper. An ordinary pocket magnifier is employed in the search, and the 

 shells are readily seen against the black background. For removing them I always 

 employ a single bristle, stuck into a handle one taken from a shaving-brush is, per- 

 haps, the best adapted to the purpose and take up the shells singly by wetting the 

 tip of the bristle. 



There is also another method whereby the empty shells may be obtained in consider- 

 able numbers. The sand, mud, or other substance, in which they reside, should be well 

 dried, heated, and then stirred into water. As the chambered cells of the Rhizopods 

 will be filled with air, they will float on the surface of the water, and can be skimmed 

 off without much difficulty. 



The first sub-class of these beings is the Foraminifera, so called on account of the 

 tiny openings, or Foramina, with which the pretty shells are pierced. Sometimes, 

 however, this shell is wanting, and its place supplied by a cover composed of matted 

 sand-grains. The greater number of these creatures are found by a succession of buds, 

 each bud remaining in connection with that from which it sprung, and thus forming a 

 composite body, which sometimes is rather complicated in its structure. Sometimes, 

 when the buds are merely arranged in a line, the result is a straight, rod-like form, 

 divided into a series of joints, marking the spots where the buds have in their sequence 

 issued from each other. If, on the other hand, each bud grows a little on one side of 

 its predecessor, a spiral form is the result, and a nautilus-like shell is formed. The 

 resemblance to this mollusc is further increased when each but becomes rather larger 

 than that from which it sprung. 



The arrangements of the Foraminifera hitherto in use have mostly been founded 

 upon the mode of growth ; but Dr. Carpenter has clearly shown that this character is 

 so extremely variable, that no reliance can be placed upon iv. In a single genus there 

 is every gradation between the straight and the spiral forms ; and, in many instances, 

 a shell which commences in a spiral will end in a straight line. 



As, therefore, the already existing systems have been shown to be based on false 

 principles, and the arrangement which is to supplant them has not been fully decided 

 upon, we will not occupy our space by insisting upon the characters by which the 

 systems are established, but merely proceed to a brief description of the localities in 

 which the various species of our illustration may be found. 



The greater number of the species represented in this illustration are found in 

 England, and may be recognized by means of the figures, among which may be men- 

 tioned the genera which are now known by the names of Dentalina, Polystomella, 

 ilina, and Quinqueloculina. The remaining species are to be found in Central 

 America. 



