A. EAKLAND ON RADIOLARIA. 263 



elliptical discs, concentrically laminated and highly refractive^ 

 resembling starch grains. Twin forms have been observed, as 

 though they were in process of division. Their constitution and 

 value are unknown. 



Intra-capsular Xanthell.e. 



The xanthell^e or symbiotic yellow cells are found in the 

 central capsule of one legion only, the Acantharia. In the other 

 three legions they occur only in the extra-capsulum. Their 

 nature and significance will be discussed later on. 



The Extra-Capsulum. 



The extra-capsulum includes all those parts of the soft bod}'^ 

 which are outside the central capsule, and may be regarded mainly 

 as the organ of nutrition and motion. It consists of the following 

 constant parts: — (1) The calyiiima or "jelly- veil"; (2) Theexoplasm 

 or extra-capsular sarcode, which may be subdivided into (a) The 

 sarcomatrix or layer of exoplasm immediately surrounding the 

 membrane of the central capsule ; (h) the sarcoplegma or irregular 

 network of exoplasm ramifying through the calymma ; (c) the 

 sarcodictyum or netw^ork of exoplasm covering the outer surface 

 of the calymma ; (d) the pseudopodia, which, originating in the 

 sarco-matrix, pierce the calymma, on the outer surface of which 

 they form the network of the sarcodictyum, thence radiating 

 freely from its nodal points into the surrounding water. 



Besides these two constant elements, the extra-capsulum very 

 frequently but not invariably includes certain other enclosureSy. 

 such as : — 



(3) An external or extra-capsular skeleton. 



(4) Extra-capsular vacuoles or alveoli. 



(5) Fat granules or oil globules. 



(6) Pigment granules, or in the fourth legion the peculiar body 

 known as the phceodium. 



(7) Xanthell^. 



The Calymma. 



The most voluminous portion of the extra-capsulum is the 

 calymma, or thick gelatinous mantle which completely surrounds 

 the central capsule, from the outer surface of which, however,. 



