xliv THE VOYAGE OF H.M.S. CHALLENGER. 



of nutriment. In the latter respect they are of special importance in the process of 

 spore-formation, each flagellate spore usually containing a fat-granule. 



74. The Intracapsular Pigment-Bodies. In the majority of Radiolaria when observed 

 alive, the central capsule is coloured, only in the minority is it colourless. The colour is 

 never diffuse, but always due to the formation of definite pigment-granules or vesicles, 

 which are sometimes distributed evenly throughout the endoplasm, sometimes aggregated 

 in the central or peripheral regions. Their form may be either spherical, irregularly 

 rounded, or polyhedral. They vary much in dimensions, but in most cases are im- 

 measurably small, and appear under a high magnifying power as fine dust ; occasionally, 

 however, their diameter may amount to from O'OOl to O'OOS or more. The chemical con- 

 stitution of the intracapsular pigment is unknown in most Radiolaria, and is probably 

 very various. In many instances the pigment-granules consist of fat, in others not. The 

 commonest colours are yellow, red, and brown ; violet and blue are rare, and green still 

 rarer. Sometimes a definite tone of colour prevails throughout a whole group, and may 

 then be attributed to inheritance, e.g., red is found in most Sphaeroidea, and blue in 

 the Polycyttaria (see note A). One colour is almost always constant in the members 

 of the same species. True pigment-cells, belonging to the Radiolarian organism, do not 

 occur within the central capsule. The peculiar yellow cells which are found in the 

 central capsule of many ACANTHARIA are symbiotic xanthellse (see 76). 



A. The number of Kadiolaria whose pigment has been examined in the living state, is too small 

 to allow of any general conclusions being drawn. Eegarding the different colours known, see my 

 Monograph, L. N. 16, p. 76. 



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 PH^ODARIA), 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 

 Collosphcera huxleyi, and regarded as coelestin. They are also found in the central 

 capsule of many other CollosphaBrida, e.g., Buccinosphcera (PL 5, figs. 11, 12). Crystal- 

 masses, crystal-sheaves, or spherical masses of radiating acicular crystals are enclosed in 



