RHIZOPODA. 



9 



The " yellow cells " which are almost invariably found in the Radiolaria, either 

 within or without the capsule, have been the subject of much speculation. It is not yet 

 known what their functions are, and it is even doubtful if tliey are not parasitic plants, 

 taking their nourishment fi-om the body of the Radiolarian in which they live. After 

 the death of the animal the yellow cells have been observed to gi'ow and multiply. 



With the exception of a very few species of Thalassicolla, Thalassolampe, Myxo- 

 hrachia, and Collozoum, all the Radiolaria are provided with some form of silicious 

 framework. In its simplest form this consists of isolated spicules, as in Sphmrozoiini, 

 Fig. 9. From the simple spicular fonns we may pass to those having sjiines radiate 

 ing from a coirunon centre to the surface of the sphere, or beyond, with lateral jirocesses 

 like Xiphacantha, Fig. 7. 





/ ' / / 



Fig. 5. — Eucecryphialus gegenbauri, greatly enlarged. 



In certain species the skeleton is formed of hollow spines, through which the sarcode 

 extends and issues from the ends. In all cases the spines are covered with a thin layer 

 of granular sarcode, which can be observed constantly flowing up and down the spines, 

 doubtless carrying the food that may be collected, down into the body. 



As the lateral processes mentioned above become more largely developed, a con- 

 tinuous circumferential skeleton is formed, which encloses the whole organism, as in 

 Actinomma, in which there are sometimes three or more concentric shells. Among 

 the Polycystina there is a great variety of form manifested in the external skeleton. 

 Podoc)/rtis (Fig. 8) is one of the most common fonns of this group. 



Tiie food of the Radiolaria consists of minute algaj, diatoms, infusoria, and otlier 

 organisms found on the surface of the sea. 



Not much is known concerning the methods of multiplication among the Radiolaria. 

 It m.ay be accepted as an established fact that the contents of the capsules may divide 

 and form young capsules, which are at first without any membranous covering. The 

 young capsules make their way out, swim about freely as " zoospores," which, in Col- 



