A. EARLAND ON RADIOLARIA. 265 



which, by very largely increasing the volume of the calymma, 

 must at the same time increase its power of mechanical 

 resistance, has been developed as a means of protection, and in 

 lieu of the ordinary defensive skeleton. 



Fat granules are widely distributed in the exoplasm of Radio- 

 laria, appearing usually as small, dark, highly refractive bodies, 

 sometimes coloured. They are very likely products of digestion. 

 Larger oil globules also occur, especially in the social Kadiolaria 

 (Polycyttaria), in which they are sometimes abundant. 



The formation of extra-capsular pigment is rare apart from 

 the ph^eodium of the Phseodaria. Considerable masses of pigment, 

 usually black or blue, rarely brown or red, are found in a few 

 Radiolaria. The composition and value of these exceptions to the 

 rule are unknown. 



The Ph^odium of the Phseodaria. 



The fourth legion, the Phseodaria, is distinguished from all 

 other Radiolaria by several special features, such as the possession 

 of a double membrane of the central capsule, the peculiar structure 

 of the main opening or astropyle, and the constant presence of a 

 large mass of extra-capsular pigment. This mass has been called 

 the Phseodium, and the constituent granules Phseodellse. It 

 possesses a peculiar constitution and significance, which separate 

 it entirely from the extra-capsular pigment granules observable 

 in many other Radiolaria. The phaeodium is always excentric in 

 position as regards the central capsule, surrounding the oral half 

 in the form of a voluminous concavo-convex cap, and hiding the 

 astropyle at the basal pole of the capsule so completely that it is 

 rarely visible until the phaeodium has been removed. The central 

 capsule is generally almost entirely imbedded in the phaeodium, so 

 that only its aboral pole projects. The ** proboscis," which in all 

 Phaeodaria rises from the astropyle, is entirely surrounded by the 

 phaeodium, the volume of which is generally about equal to that 

 of the central capsule, though occasionally it is much larger. 



In colour the phaeodium is always dark, usually olive green or 

 blackish brown, rarely reddish brown or black. It consists of a 

 mass of large and small phaeodellae varying from hundreds to 

 thousands in number. They differ in size as well as in intensity 

 of colour, and are irregularly crowded in a black powder-like 



