Ernst Haeckel

“ The Membrane of the Central Capsule.—The capsule-membrane or envelope of the central capsule is both morphologically and physiologically one of the most important parts of the Radiolarian body, for it separates its two main constituents, the capsule with its nucleus and endoplasm and the extracapsulum with the calymma and exoplasm. The capsule-membrane is invariably present at some time or other during the life of the organism, even though in a few species it may persist only for a short time. ”

“ I could distinguish only four species, two of which are cosmopolitan and very widely distributed. In all four species the diametral spines are quite simple, cylindrical; only in one species distinguished by a spiral winding or torsion in the middle part, where they are crossed one to another. We derive Acanthochiasma from Acanthometron by concrescence of every two spines opposite in one axis of the body. ”

“ A very difficult matter is the mode of connection between the cortical and medullary shell. In most of the Pylonida it seems that the first or transverse girdle (in each system) is produced by the formation of two lateral wings or chambers (one on each side of the medullary shell) , so that each wing (or half girdle) represents a short and wide, nearly cylindrical tube, the axis of which (with free openings on both poles) is parallel to the principal axis of the medullary shell. ”

“ The Nucleus of the Actipylea.—The nucleus of the Acantharia or Actipylea shows very peculiar relations in respect of structure and division, particularly special forms of lobular budding, which belong to the characteristic peculiarities of this singular legion, and are not found among other Radiolaria. The position of the nucleus is always excentric, even in the youngest Acantharia, for the centrogeneous formation of the skeleton, the constant development of the earliest radial portions of it in the middle of the central capsule, forces the nucleus from its normal central position. ”

“ Among the Miocene Radiolaria numerous species, both of Spumellaria (especially Sphæroidea and Discoidea) and of Nassellaria (especially Spyroidea and Cyrtoidea) are not to be distinguished from the corresponding still living forms (see notes C, D) . On the other hand, those genera, which are rich both in species and individuals (recent as well as fossil) , present continuous series of forms which lead gradually and uninterruptedly from old Tertiary species to others still living, which are specifically indistinguishable from them. ”

“ The genus Orophaspis differs not only from its ancestral form, Dorataspis, but from all other Dorataspida in the development of peculiar free apophyses on the radial spines, outside the shell. These apophyses, two being opposite on each spine, appear as a repetition of the primary apophyses of Phractaspis; they are either simple or branched, and sometimes the branches are united together, forming an outer free shield with two or four pores. These outer plates represent the beginning of a second outer shell and form the transition to Phractopelta, the ancestral form of the Phractopeltida. ”

“ The family Liosphærida comprises all those solitary Sphæroidea in which the surface of the spherical shell is not armed with radial spines. Nearly the half of this large group is formed by the Ethmosphærida, in which the carapace is a quite simple, spherical lattice-shell; this subfamily is probably the common ancestral group from which all other Sphæroidea, or even all Sphærellaria, can be derived in a phylogenetical as well as in a morphological sense. The central capsule in this first subfamily is constantly enclosed by the fenestrated shell, and separated from it by the jelly-veil. ”

“ Natural and Artificial Systems.—Although in the classification of the Radiolaria, as in the case of all other organisms, the natural system must be regarded as the goal of systematic classification, our phylogenetic knowledge of the Radiolaria is too fragmentary and inadequate to admit of the systematic arrangement here adopted being regarded as a thoroughly consistent natural system, that is, as representing the true genealogical tree of the class. ”

“ Perpendicular to this axis is the equatorial plane of the disk by which it becomes divided into equal halves. In the simplest forms of Discoidea all axes of this horizontal equatorial plane (all "equatorial axes" or "cross axes") are equal; in the most of the genera and species these cross axes are different, so that rays of stronger growth ("perradii") alternate with rays of weaker growth ("interradii") . The number of these cross axes distinguishable is commonly two to four, rarely more. In the direction of these are developed either radial marginal spines or spongy arms. ”

“ Usually the twenty bases seem to remain free (supported one upon another by means of their triangular faces) ; but sometimes they seem to grow together perfectly and to form a single central star of acanthin. In some species, too, the sutures of the meeting branches of the apophyses of neighbouring spines seem to grow together, so that the whole shell exhibits a single piece of acanthin.
The Central Capsule of the Hexalaspida is therefore very small and seems to fill up the greatest part of the shell-cavity. Its form is constantly more or less lenticular, sometimes lentelliptical. ”

“ The promorphology of the Acantharia demonstrates that the geometrical fundamental form in those groups is different. In the majority of the Acantharia, where the two equatorial axes are equal, that form is a double square-pyramid or a "quadrate octahedron"; the four equal equatorial spines indicate the two diagonals of the square, which is the common base of the united regular four-sided pyramids; their common axis is the spineless axis of the body; the ends of the polar spines fall on the edges of the pyramids, while the ends of the tropical spines fall on the halving lines of their faces. ”

“ Definition.—Pores of the cortical shell regular, of nearly equal size and similar form; spines on the whole surface (commonly one spine at each nodal-point) .
1. Haliomma hexagonium, n. sp.
Cortical shell four times as broad as the medullary shell, both having very thin thread-like bars, and regular, hexagonal pores (eighteen to twenty on the radius of the outer, five to six on the radius of the inner shell) . The two shells connected by twenty thin thread-like radial beams. At each nodal-point of the outer shell arises a bristle-shaped radial spine, half as long as the radius. ”

“ In the case of the Radiolaria as well as of many other classes of animals, the law holds good that the richest development of forms and the greatest number of species occurs between the tropics, whilst the frigid zones (both Arctic and Antarctic) exhibit great masses of individuals, but relatively few genera and species (see note A) . In the Challenger collection the greatest abundance of species of Radiolaria is exhibited by those preparations which were collected at low latitudes in the immediate neighbourhood of the equator ”

“ Types of Skeletal Formation.—No less than twelve different principal forms may be distinguished as morphological types of the formation of the skeleton in the Radiolaria; some of these are peculiar to a single legion or even to a smaller group; but sometimes the same form occurs in several legions. Some types occur only in an isolated manner, independently of the others, but most exist in various combinations with other types. Of the twelve described below the Conchoid and Cannoid occur only in the Phæodaria; the Plectoid and Circoid only in the Nassellaria; the Astroid only in the Acantharia ”

“ The suborder Colloidea comprises all those Spumellaria in which no skeleton is developed. The whole body is therefore soft—a true malacoma—and is composed only of two essential parts, the central capsule and the enveloping extracapsulum. The suborder contains only two different families, the solitary Thalassicollida (or Colloidea monozoa) and the associated Collozoida (or Colloidea polyzoa) . Both families are very nearly allied, and differ only in one single essential character: the solitary life of the former, the social union of the latter. ”

“ But the symbiosis of the Xanthellæ and Radiolaria is not as in the lichens a phenomenon essential for their development, but has more or less the character of an accidental association. The number of the inquiline Xanthellæ is so variable even in one and the same species of Radiolaria, that they do not appear to be exactly essential to its welfare; and in many species they are entirely wanting. ”

“ Here the actual Bion (or the fully developed physiological individual) is not represented by the individual cells, but by the whole multicellular cœnobium, which in each species has a definite form and size. In these cœnobia, 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. ”

“ Each cone is prolonged into a very thin, irregularly curved radial spine, which is twice as long as the shell diameter, simple in the proximal half, branched like a tree in the distal half; each arborescent spine has from sixteen to thirty-two terminal branches, which fall in one spherical face. The branches of neighbouring spines are partly connected by anastomoses, so that they begin to form an outer spherical shell (cortical shell) with a looser spongy framework. ”

“ The Central Capsule of the Spongurida is either ellipsoidal or cylindrical. Only in Spongellipsis it lies freely in the internal cavity of the spongy shell. In all other genera it is perforated by a part of the skeleton; in the Spongodruppida it contains the simple or double medullary shell, and the radial beams which perforate its membrane and connect the latter with the external spongy cortical shell. In Spongurus and the allied genera (Spongocore, Spongoprunum) the whole central capsule is filled with a spongy framework which also envelops its surface. ”

“ In the wider sense, given originally to Acanthometra by Johannes Müller, its discoverer, this genus comprised all Acantharia constituting here our order "Acanthometra" (Radiolaria without lattice-shell, with radial spines united in the centre) . In my Monograph (1862, p. 375) I restricted this genus to those "Acanthometrida" in which twenty simple spines of equal size (and without apophyses) are supported one upon another in the centre, and I separated as Astrolithium those forms in which they are grown together in the centre. ”

“ The apophyses of the twenty radial spines, the branches of which compose the ellipsoidal lattice-shell, exhibit in all Belonaspida the same appearance as in the Diporaspida (and especially the Ceriaspida) among the spherical Dorataspida. Everywhere each radial spine gives off only two opposite primary apophyses, the fork-branches of which unite together and form a plate or shield with two aspinal pores (as in Dorataspis) . Commonly the shell exhibits only these forty parmal pores, the other meshes between them being sutural pores. ”

“ In the Polycyttaria (or social Spumellaria, i.e., the three families Collozoida, Sphærozoida, and Collosphærida) , the cause of the adaptation lies most probably in the formation of the colony itself, for all these three families are so closely related to three corresponding families of serotinous, monozootic Radiolaria (Thalassicollida, Thalassosphærida, Ethmosphærida) , that certain species of the latter are hardly to be distinguished from isolated individuals of the former. ”

“ Of the four legions of the Radiolaria, the Acantharia (on account of the solubility of their astroid acanthin skeletons) have entirely vanished and have never been found fossil. Of the Phæodaria, whose silicate skeleton is not as a rule capable of fossilisation, only one section (Dictyochida) of a single family (Cannorrhaphida) has been observed fossil. Hence the fossil remains of the Radiolaria belong almost exclusively to the two legions, Spumellaria and Nassellaria, which were formerly united under the term "Polycystina." ”

“ The Skeleton consists in all Spumellaria either of pure silica or of a peculiar silicate. The siliceous bars and beams constituting it are invariably solid, as also in the Nassellaria, never hollow, as in the Phæodaria. Never is the skeleton composed of acanthin, as in all Acantharia. Whilst in the first order of Spumellaria, Collodaria, the form of the spicula, or the scattered needles, composing the skeleton, is very simple, never latticed, in the second order, the Sphærellaria, it is constantly latticed or fenestrated, often also spongy. ”

“ No doubt the Zygartida must be derived from the Panartida by progressive growth of the cortical shell in the main axis and accompanying increase of the number of its chambers. Whilst this number in the Panartida is constantly restricted to four, in the Zygartida it amounts to ten, twenty, or more, and is in the lowest case six (Pl. 40, fig. 10) . The maximum number is variable in the different species, but of course also different in the various degrees of individual development. Each Zygartid is at the beginning of its growth a Cyphinid, later a Panartid. ”