75. _The Intracapsular Crystals._--The crystals found in the central capsule of many Radiolaria may be divided into two groups, of very different significance; small crystals, which are very widely distributed, and large crystals, which occur in only a few genera. The _small crystals_ may also be termed "spore-crystals," since each swarm-spore often contains such a crystal. They are rod-like or spindle-shaped, and consist of an organic substance which probably serves as a reserve of nutriment for the developing spores. Such spore-crystals have been observed in numerous SPUMELLARIA and ACANTHARIA belonging to various families, and are probably present throughout the two legions which make up the Porulosa. On the other hand, they have not been noticed in the Osculosa (NASSELLARIA and PHÆODARIA), the few swarm-spores belonging to these groups which have been observed not exhibiting any crystals. The _large crystals_, which occur in small numbers in the endoplasm, have hitherto only been observed in a few species of SPUMELLARIA, belonging to the Polycyttaria. They were first noticed in the common _Collosphæra huxleyi_, and regarded as coelestin. They are also found in the central capsule of many other Collosphærida, _e.g._, _Buccinosphæra_ (Pl. 5, figs. 11, 12). Crystal-masses, crystal-sheaves, or spherical masses of radiating acicular crystals are enclosed in {xlv}the vacuoles or "albumen globules" of _Thalassicola nucleata_ and other Thalassicollida, as well as in the central capsule of _Coelographis_ and some other PHÆODARIA (Pl. 127, figs. 4-7). All these large crystals are probably to be regarded as excretory products. 75A. _The Intracapsular Concrements._--Concretions, either mineral or organic, of varying form and constitution, are to be found in the endoplasm of Radiolaria belonging to very different families. They are most abundant and multiform in _Thalassicolla nucleata_, being usually circular or elliptical discs, which are concentrically laminated and highly refractive, resembling starch-grains. Among them twin forms may frequently be observed, as though the concrements were in process of division (see note A). Similar amyloid concretions are to be seen in the central capsule of different SPUMELLARIA and NASSELLARIA, _e.g._, in _Cephalospyris triangulata_ (Pl. 96, fig. 28). Violin-shaped, highly refractive concrements have been observed in the central capsule of numerous SPUMELLARIA, NASSELLARIA, and ACANTHARIA, _e.g._, _Thalassosphæra_, _Spongosphæra_, _Plegmosphæra_, _Cyrtocalpis_, _Peripyramis_, _Botryocella_, &c. (see note B). The chemical constitution of these concrements is insufficiently known. A. The amyloid concretions of _Thalassicolla nucleata_ have been described in detail in my Monograph (pp. 80, 250, Taf. iii. figs. 2, 3), and by R. Hertwig in the Histologie der Radiolarien (1876, p. 47, Taf. iii. figs. 9-13).