REPORT ON THE RADIOLARIA. liii 



resistance to meclianical influences and almost disintegrating under the eyes of the 

 observer, and on the other hand forming a firm gelatinous shell, comparable to cartilage 

 in hardness, elasticity, and power of mechanical resistance. In many Radiolaria of 

 large dimensions with an alveolar calymma (especially in numerous Collodaria and 

 Ph^odaria) this may be split by means of dissecting needles and the central capsule 

 extracted like the stone from a cherry, and then it is easy to ascertain that the firmness 

 and elasticity of this jelly-veil are not less than those of a cherry. The diff"erent 

 degrees of consistency in the various Eadiolaria may be dependent either upon the 

 relative amount of water which they contain, or upon qualitative or quantitative 

 variations in the organic substance of which the jelly consists. Great importance is to 

 be attached to the considerable consistency of the calymma, because it furnishes the 

 indispensable groundwork for the deposition of many parts of the skeleton and parti- 

 cularly of the lattice-shells. 



85. The Primary and Secondary Calymma. — In most Radiolaria the external 

 form and volume of the calymma are different at different stages of growth, and this 

 difference is mainly dependent upon the development of the skeleton. Hence it is ad- 

 visable to distinguish in general the primary from the secondary calymma. The primary 

 calymma is in the great majority of Radiolaria a perfect sjahere, in the middle of which 

 lies the concentric central capsule ; on the surface of this gelatinous plate the primary 

 spherical lattice-shell is secreted in most Spumellaria and Acanthophracta, as 

 well as in those Ph^odaria which possess a spherical shell ; in the remaining PniEODARiA 

 also and in the Nassellaria, where the lattice-shell is not spherical but monaxon, it is 

 secreted on the surface of the primary calymma. This takes place at a definite time, 

 very important in the development of the Radiolarian, which for the sake of brevity we 

 shall term the " lorication-period." Since the firm surface of the primary calymma 

 furnishes the necessary foundation for the deposition of the primary lattice-shell, it is of 

 the greatest mechanical significance in all shell-bearing Eadiolaria. The secondary 

 calymma arises only after the lorication-period by further growth of the primitive jelly- 

 mantle and in the fully developed Radiolarian usually encloses wholly or partially the 

 external parts of the skeleton, in consequence of which it assumes the most various 

 forms. Very often the secondary calymma is polyhedral, being stretched between the 

 radial spines of the skeleton, the distal ends of the latter then forming the fixed points 

 of the gelatinous polyhedron. 



86. Tlie Exti'acapstdar Vacuoles and Alveoles. — The calymma of the Radiolaria 

 usually appears completely homogeneous and hyaline without any structure ; some- 

 times it encloses numerous clear vesicles, vacuoles or alveoles, and then assumes a 

 frothy appearance, the expression of a more or less distinct alveolar structure. 



