Rhizatnmina has a free branching tube open at the ends; so too Sagenella, but the branches anastomose and the test creeps over some foreign object. The two genera Botellina and Haliphysema stand by themselves. As to the former, the test is probably attached; it is more or less straight, expanded, and thin at the free end, where there are interstitial apertures; the rest of the tube is thick-walled and traversed by irregular sandy partitions. Haliphysema has an expanded base from which spring one or more columns, simple or branched, and somewhat swollen at the extremity.
The protoplasm is typically of a uniform granular character throughout; but Shepheardella and Lieberkiihnia are said to have a delicate clear superficial layer. Currents in it have been observed in some forms. It is often colourless, but it is brown in many Miliolidae, olive-green in many arenaceous forms from the deep sea, and Orbitolites tenuissima, greenish in O. complanata, reddish or red-brown in O. duplex, and many others. But the last-named colour is perhaps derived from the food, which consists chiefly of Diatoms1. The pseudopodia are typically fine filaments which branch, anastomose, and extend to a great distance. They show currents of granules flowing outwards and backwards simultaneously in the same pseudopodium. When the test is imperforate they originate as a rule from its aperture alone, whether single, double, or multiple; in Microgromia and Lieberkiihnia from a pseudopodial peduncle or compact process extended from the mouth of the test. In the Gromidae, except Microgromia, there are also pseudopodia given off from the surface of the test, probably through perforations in it in Diaphoropodon, but in Lieberkiihnia and Gromia itself, where they are plentiful, and Shepheardella, where they are few, from a layer of protoplasm which flows from the aperture round the test.
Those which radiate from the surface of the test in Diaphoropodon are fine, straight, linear, short; those which originate from the mass of protoplasm at the mouth of the test form a dense radiant bundle and branch slightly, but if the organism is disturbed some of them become of great length and tufted at several points. The protoplasm in all perforate genera forms a superficial coat from which the pseudopodia are given off, and issues not only from the aperture but the pores of the test, as well as from the interseptal canals when present, a rule to which the genus Lagena is possibly an exception; L. elegans certainly is so (Butschli). In the pelagic Hastigerina Murrayi, and probably in some other pelagic species, this coat is filled with large non-contractile vacuoles, such as are seen in the extracapsular protoplasm of many Radiolaria. The pseudopodia are organs of locomotion as well as of alimentation. Foreign bodies when sufficiently small may be drawn within the test; but they are very generally, in many instances indeed necessarily, digested outside it.
Minute non-contractile vacuoles have been observed in Shepheardella and Spirillina; a single contractile vacuole in some species of Gromia, in Microgromia and Diaphoropodon. It is said that the vacuoles of Lieberkiihnia eventually come to the surface and burst. Vacuoles which change in shape and disappear, whilst others appear in their stead, have been observed in some marine genera, e. g. the Miliolid Biloculina (Butschli).
1 The colouring matter exists either in the form of minute particles, or collected in distinct vesicles, but the latter may be symbiotic algae. See p. 894 infra. The oldest chambers are the most intensely coloured, the newest being generally colourless. The colour disappears more or less completely on deprivation of food, and is restored when it is plentiful. The chemical reactions of the reddish colour are like those of Diatomin; see Max Schultze, 'Organismus,' pp. 19-20.
All Foraminifera properly examined have been found to possess a nucleus, and at first one only - a fact to be carefully noted, as showing that polythalamous genera are neither truly segmented nor colonial1. In them the nucleus appears to wander by degrees into the outer chambers from the primordial chamber where it is primitively situated. Both mono- and poly-thalamous genera however become multinucleate sooner or later, and the nuclei are thereupon scattered through the chambers if there is more than one. The increase of the nuclei in number is probably connected with reproduction (infra). The nucleus has a membrane with contents usually described as homogeneous or finely granular, but in well-prepared specimens there is a distinct chromatin network, with one or more nucleoli (Butschli). In Trochammina (Rotalina) inflate and in an Ovulina, one half of the nucleus has been found to consist of chromatin, the other of a non-staining substance.