Binary fission has been observed only in Lieberkiihnia and Micro-gromia2. In the former it is transverse, and the delicate test undergoes division with the body; in the latter it is either transverse or longitudinal. When it is transverse the hinder part quits the test and becomes either amoeboid or ovate and biflagellate. When longitudinal, both parts are in connection by their pseudopodial peduncles; one quits the test but remains a member of the colony; it sometimes undergoes a previous subdivision into two. Portions of the disc in Orbitolites, accidentally broken off, continue to live and form new and completely concentric annuli. A mode of reproduction to be regarded as spore-formation (?) has been observed in various calcareous Foraminifera - Miliolina, Peneroplis, Orbi-tolites complanata, Cristellaria, Spirillina, and a Rotalid, representatives of both imperforate and perforate genera. There appear within the adult minute young with calcareous tests, single-chambered in Miliolina, Spirillina and Peneroplis, three-chambered in the Rotalid, with the first ring of chambers complete in Orbitolites. Similar young of Miliolina and Rotalia have been found free, and been proved to be uninucleate by Hertwig, the nucleus lying in the primordial chamber of the Rotaliae. There can be little doubt that the young in question take origin by the multiplication of the nucleus, the separation of protoplasm round the nuclei thus formed, and the deposition of a test; they are then set free at the aperture of the parental test, or, if this is represented by pores, as in Peneroplis, by solution of the walls of the chambers containing them 1.
1 The monothalamous Lieberkiihnia, Haliphysema and Spirillina are known only in the multinucleate state.
2 It is not likely that abortive attempts at fission are indicated in the double shells seen sometimes in Lagena, the partially divided coils of Polystomella, the bifid discs of Orbitolites com-planata, or the half-discs set on the normal discs in that Foraminifer. They are probably simply irregularities of growth. To what an extreme such irregularity may be carried, see von Roboz' account of Calciluba in SB. Wien. Acad 88, Abth. 1, 1884.
A colonial state occurs in Microgromia socialis, where a number of individuals remain united by their pseudopodia. When the latter contract, as they do on irritation, the tests are drawn into a heap, and in this condition the organism was described by Archer as Cystophrys Haeckeliana, in its expanded state as Gromia socialis. Young Miliolinae were observed by Hertwig associated to the number of 30-40 by a protoplasmic mass, from which pseudopodia streamed in all directions. Conjugation has not been observed, unless the apposition of young Miliolinae in twos, recorded by Gervais, is an instance.
The majority of Foraminifera are marine, but some of the marine species are capable of living in brackish water, with very slight admixture of salt, and two (Polystomella striatopunctata, Nonionina depressuld) have been gathered even in perfectly fresh. Microgromia and Diaphoropodon are entirely freshwater, Lieberkiihnia and Gromia inhabit both fresh and salt. One species, Entzia tetrastomella, has been found in salt pools in Transylvania. The only terricolous form known, Gromia terricola, was discovered by Leidy amidst damp moss in the cracks of a pavement in Philadelphia. In the sea the Foraminifera are universally distributed and at all depths, arenaceous forms proper, i. e. Astrorhizidae, being for the most part inhabitants of the deep sea, where also the Lituolidae attain their highest development in size and complexity. The largest and most specialised calcareous genera are found in the shallow waters of tropical and sub-tropical seas. A few calcareous forms are pelagic, principally species of Globigerina, Orbulina, Pulvinulina, Ptdlenia, and the genus Hasti-gerina, all members of the family Globigerinidae. It is their tests which, together with those of some non-pelagic species, in small proportions however, make up the Globigerina ooze, or modern chalk, which is undergoing deposition at the present time over immense surfaces of the sea-bottom, at depths ranging from 250 to 2900 fathoms, especially from 1000 to 2000. There is reason to suppose that pelagic forms, with the exception probably of Hastigerina, are capable of living also at the bottom.
Foraminifera are also met with in the two other deep-sea deposits, Radiolarian Ooze and Red Clay. Their fauna is approximately identical according to Brady, in some instances differing little from that of Globigerina ooze, though naturally in relatively smaller proportion to the characteristic materials of the two deposits in question. The tests of the pelagic forms however which they contain are worn and corroded. In two dredgings made by H.M.S. 'Challenger' in the Pacific, both in mid-ocean, arenaceous species occurred almost exclusively; in two others minute and highly ornamented Lagenae were abundant. Foraminifera are common in marine geological deposits, and a large number of living genera make their appearance at an early period - Textidaria, Lagena and Nodosaria in the Silurian, Cor-nnspirci) Lituola, Trochammina, Calcarina, Nummulites, etc, in the Carboniferous, Miliolina and Globigerina in the Trias, a very large number of forms in the Chalk, and especially in the Tertiary period. Alveolina, Operculina and Nummulites are genera which, though living at the present day, were particularly numerous in Eocene times; and the last-named especially contributes largely to the building up of limestones of that age in Central Europe, Central and Southern Asia, and Northern Africa. Many arenaceous genera (Astrorhizidae and Lituolidae), still living in the deep sea, are found in the Lias and attain their maximum development before the Cretaceous period.
Of extinct forms, one Eozoon, of doubtful animal nature however, is found in Pre-Cambrian strata. It is supposed to have consisted of tiers of more or less oval chambers with perforated walls, connected by vertical canals and an intervening supplemental skeleton with interseptal canals; the chambers in each tier have usually wide openings into one another; the whole structure covered surfaces a foot square with masses 5-6 in. thick. Among Lituolidae the Endothyrinae extend from the Carboniferous into the lower Oolite; Parkeria is confined to the Greensand, Loftusia comes from the Carboniferous limestone of British Columbia and Eocene strata in Persia. Fiisulina is Carboniferous and Permian; Orbitoides occurs in Cretaceous strata, in Eocene, where it is very frequent in Nummulitic limestone, whilst in Miocene it is rare. Chalk is a fossilised Globigerina ooze; in some specimens of it Globigerinae form 90 per cent, at least of the bulk. They are found also in some of the Barbadian marls. The majority of Foraminifera are of moderate size, below 1/2 in.; many are microscopic; Cycloclypeus Carpenteri, the largest living species, measures rather more than 2 in. across the disc; Parkeria and species of Orbitoides and Nummidites attain a diameter of 2 in.; Loftusia is fusiform and 3 in. long.
A symbiotic Zooxanthella has been observed in Globigerina eckinoideSy brownish cells in a Peneroplis, minute nucleated cells in Or hi-tolites complanata, as well as others of larger size, possessed of a distinct membrane, within which the cell undergoes fission. Diatoms retaining their soft parts have been found by Biitschli in the last-named species.
1Ray Lankester found in the anterior part of Haliphysema Tumanowiczii nucleated egg-like bodies (Q. J. M. xix. p. 482), and Saville Kent describes in the same Foraminifer minute amoebi-form young, naked pyriform bodies, and every stage to the adult (A. N. H. (5), ii. p. 76). It is possible that the 'ova' described by some older authorities in various genera are young in an early stage. The protoplasm of the parent may or may not be completely used up in the reproductive process. In Orbitolites the young lie in the peripheral annulus, the outer wall of which is described by W. B. Carpenter as very thin, and its cavity undivided by septa into chamberlets. The number of young is sometimes very great, e. g. in a Peneroplis Proteus described by Schacko it was 118, all contained in the fourteen terminal chambers. Many specimens of the Globigerinid Orbulina, which has the form of a perfect sphere, with, in some instances, an aperture, contain adherent to the inner surface a Globigerina with a number of chambers, up to 13-14, the larger chambers being spinulose. Such inclosures are most common in small and middle-sized specimens, whilst in large they are either absent or scarcely indicated; they are found both in recent and fossil specimens.