264 A. EARLANI> ON RADIOLARIA. 



it i8 separated by a thin but continuous layer of exoplasm, the 

 sarcomatrix. The calymma is difficult to detect in the living 

 Kadiolarian, for the gelatinous substance of which it is composed 

 is perfectly pellucid and colourless, and possesses the same refrac- 

 tive index as sea-water. Its presence may be demonstrated by 

 staining the specimen with carmine, which penetrates very slowly 

 into the mass. In dead specimens it is more readily observed, 

 owing to the fine particles of matter which adhere to its viscid 

 surface. 



The calymma of most Radiolaria appears as a fine structureless 

 mass, containing neither fibres nor enclosures. In some groups, 

 however, definite structural characters become developed. The 

 most striking is the formation of alv^eoles, which in some cases are 

 so numerous that the calymma assumes the appearance of a frothy 

 mass composed of large, clear, thin-walled vesicles. Occasionally 

 the calymma appears to be built up of thin concentric laminae ; 

 this perhaps may be due to difiering quantities of water in succes- 

 -sive layers. 



In consistency the calymma varies from a very soft jelly, offer- 

 ing little resistance to pressure, to a firm gelatinous shell, almost 

 cartilaginous in its hardness and elasticity. 



The form and volume of the calymma varies at difterent times 

 in the life history of the Radiolarian. In most forms it originates 

 as a sphere, in the centre of which lies the central capsule. On 

 the outer surface of this spherical or primary calymma, the 

 primary lattice shell is dej^osited in nearly all Radiolaria. Hence 

 it will be seen that the firmness and elasticity of the calymma 

 has considerable mechanical significance in the skeleton-forming 

 Kadiolaria. After the formation of the primary skeleton, the 

 jelly-veil continues to grow, until at last in most forms it encloses 

 and surrounds the whole of the shell, assuming in consequence 

 the most varied forms. 



As already mentioned, the calymma may contain both vacuoles 

 and alveoles. In structure and contents they resemble those in 

 the central capsule which have already been described. Their 

 size varies greatly, but as a rule large vacuoles are extremely 

 rare, except in certain groups, all of which belong to the skeleton- 

 less Radiolaria. In these groups the vacuoles and alveoles lie 

 usually in layers increasing in size from the centre outwards. 

 It seems possible that in these groups the alveolar structure, 



