A. EARLAXD OX RADIOLARIA. 267 



body, and their consequent morphological differentiation. The 

 extra -capsular protoplasm, like the intra-capsular, is originally 

 homogeneous, but it afterwards becomes differentiated in various 

 ways, producing special constituents such as vacuoles, pigment 

 bodies, etc. The following parts may, as a rule, be topo- 

 graphically distinguished : (1) The Sarcomatrix, or fundamental 

 layer of protoplasm, which forms a continuous sheath of sarcode 

 round the central capsule, separating it from the calymma ; (2) 

 The Sarcoplegma, an ii-regular network of protoplasm, which 

 ramifies through the calymma and forms (3) The Sarcodictijuriiy 

 or network of sarcode, on the outer surface of the calymma, from 

 which (4) The Pseudopodia project and radiate into the surround- 



The Sarcomatrix. 



The sarcomatrix, first described by Haeckel in 1862, forms a 

 thin contmuous mucous layer covering the whole external surface 

 of the central capsule, and separating it from the calymma. It 

 communicates with the endoplasm by means of the openings in 

 the capsule membrane. Its thickness varies considerably, even 

 in individuals of the same species, the variation being due partly 

 to the stages of development and partly to nutritional conditions. 

 After an abundance of food the sarcomatrix becomes thickened 

 and turgid, rich in granules and irregular masses, w^hich are 

 probably enclosures of undigested food. Xanthellse and other 

 foreign bodies taken up with the food, such as diatoms, smaller 

 Radiolaria, infusoria, etc., are often aggregated in considerable 

 numbers in the sarcomatrix. After long fasting, on the other 

 hand, the sarcomatrix becomes destitute of such enclosures and 

 granules. From a physiological standpoint, the sarcomatrix is 

 the most important organ of the extra-capsulum, and is probably 

 the organ of nutrition, especially for purposes of digestion and 

 assimilation. It may also be the organ of perception. The 

 sarcomatrix takes no part in the formation of the skeleton. 



The Sarcoplegma. 



By the sarcoplegma is understood that portion of the exoplasm 

 which, originating in the sarcomatrix, ramifies in a network in 

 every direction through the substance of the calymma. The 



