12. _Morphological Individuality._--From the morphological standpoint the individuality of the unicellular elementary organism is obvious in the ordinary solitary Radiolaria (Monobia), and is to be so regarded that the whole body with all its constituent parts, and not merely the central capsule, is to be regarded as _a cell_. Naturally the xanthellæ or yellow cells (§§ 76, 90), which as independent algæ live in symbiosis with many Radiolaria, must be excluded. The unicellular organisation of the Radiolaria is further to be distinguished from that of the other Protista, inasmuch as an internal membrane (capsule-membrane) separates the central (medullary) from the peripheral (cortical) portion. In the coenobia of the social Radiolaria (or Polycyttaria), the morphological individuality persists only as regards the medullary portions of the aggregated cells (the individual central capsules), while the cortical portions fuse completely to form a common extracapsulum. Hence in these SPUMELLARIA polyzoa two different stages of morphological individuality must be distinguished, the _Cell_ as a _Morphon of the first stage_, and the _Coenobium_ as a _Morphon of the second stage_.
13. _Physiological Individuality._--From the physiological standpoint also the individuality of the unicellular organism is immediately obvious in the case of the ordinary solitary Radiolaria (Monobia); as in other Protista it fulfils all the functions of life by itself alone. This physiological individuality of the monobious Radiolarian cell is furthermore not influenced by the xanthellæ, which live as independent algæ in symbiosis with many Radiolaria; even though these often by the production of starch assist in the { vii}nourishment of the Radiolaria, yet they are by no means indispensable to them. On the other hand, the physiological individuality offers more complicated relations in the social Radiolaria (Polycyttaria) which live united in colonies or coenobia. Here the actual _Bion_ (or the fully developed physiological individual) is not represented by the individual cells, but by the whole multicellular coenobium, which in each species has a definite form and size. In these coenobia, which are usually spherical or cylindrical jelly-like masses, several millimeters in diameter, numerous cells are so intimately united that only their medullary portions (the central capsule with the endoplasm) remain independent; the cortical portions (calymma and exoplasm) on the contrary uniting into a common extracapsulum. This discharges, as a whole, the functions of locomotion, sensation, and inception of nutriment, while the separate central capsules act in the main only as reproductive organs (forming spores) and partly also as the central organs of metastasis (digestion). Each coenobium may also be regarded as a polycyttarium, _i.e._, a "multicellular Radiolarian," whose numerous central capsules represent so many sporangia or spore-capsules.