A. EARLAND OX RADIOLARIA. 261 



work. In most Radiolaria, however, it very soon undergoes 

 modification, being difterentiated more or less into an internal 

 granular medullary substance and an external fibrillar cortical 

 ;substance. Various products of the sarcode also make their 

 appearance, especially the hyaline spheres (vacuoles and alveoles) 

 fat, oil and pigment granules, and occasionally crystals. 



The endoplasm is doubtless used mainly for the purposes of 

 propagation, becoming divided earlier or later into numerous 

 small particles, each of which, surrounding a particle of the 

 divided nucleus, forms with it a flagellate spore. 



Intra-capsular Hyaline Spheres. 



The central capsule of many Radiolaria contains in its 

 •endoplasm numerous spherical bodies of varying size, consisting 

 of a watery or albuminous fluid. They were originally described 

 as nuclei, but modern histological methods have disproved this. 

 They are of two kinds, vacuoles and alveoles. The vacuoles are 

 merely spherical drops of fluid, devoid of any special envelope, but 

 immediately surrounded by the endoplasm. The alveoles, on the 

 other hand, are true vesicles, enclosing a drop of fluid or jelly. 

 Both vacuoles and alveoles occasionally contain various formed 

 constituents, such as oil globules, fat granules, pigment granules, 

 crystals, etc. It may be assumed that the vesicular alveoles are 

 developed from the drop-like vacuoles by the increase in size 

 accompanied by the precipitation of a vesicular envelope from 

 the endoplasm. The character common to all hyaline spheres, 

 whether vacuoles or alveoles, is their aqueous, not adipose, 

 constitution, and their clear structureless appearance, only the 

 above-mentioned enclosures being visible in them. Their refrac- 

 tive index varies greatly, probably as the result of corresponding 

 variations in their constitution. 



Intra-capsular Fat Granules. 



All Radiolaria contain more or less fat or oil in their central 

 capsule. It generally appears as numerous small spherical 

 granules, either free in the endoplasm or enclosed in the vacuoles. 

 In addition to these small fat granules, which are always present, 

 the central capsule of many Radiolaria contains also larger fat 

 globules. They are especially notable in the Polycyttaria or 



