EEPORT ON THE RADIOLAEIA. 7 



The S p h 86 r e 1 1 a r i a differ from the C o 1 1 o d a r i a iu the possession of a perfect 

 sUiceous skeleton, which is originally a latticed spherical shell, enveloping the central 

 caj)sule. By modification of this fenestrated sphere arises an enormous mass of different 

 forms, which we dispose in twenty-eight families, and these in four larger groups, sub- 

 orders or sections, — S p h ae r o i d e a, P r n n o i d e a, D i s c o i d e a, and L a r c o i d e a. 



The Spheeroidea, the common ancestral group of the S p h se r e 1 1 a r i a, possess 

 a skeleton which is either a simple fenestrated sphere, or composed of two or more 

 concentric latticed spheres, which are united by radial beams ; more rarely it becomes 

 more or less spongy. 



The Pruuoidea are derived from the Spheeroidea by prolongation of the 

 latticed sphere in one axis ; the skeleton therefore becomes here ellipsoidal or cylindrical 

 (often with annular transversal constrictions). 



The D i s c o i d e a on the contrary must be derived from the S p h se r o i d e a by shorten- 

 inof in one axis : here therefore the fenestrated shell becomes more or less lenticular or 

 iscoidal (often with radial spines or arms in the equatorial plane, on the circular margin). 



The L a r c i d e a, the fourth section, differ from the three foregoing sections by the 

 different growth of the shell in three different dimensions of space; therefore here the 

 fenestrated shell becomes " lentelliptical," or a "triaxial ellipsoid," its length, breadth, 

 and height being different. 



The Skeleton consists in all Spumellaria either of pure silica or of a peculiar silicate. 

 The siliceous bars and beams constituting it are invariably solid, as also in the Nassel- 

 LARIA, never hollow, as in the Ph^odaria. Never is the skeleton composed of 

 acanthin, as in all Acantharia. Whilst in the first order of Spumellaria, Collodaria, 

 the form of the spicula, or the scattered needles, composing the skeleton, is very simple, 

 never latticed, in the second order, the Sphserellaria, it is constantly latticed or 

 fenestrated, often also spongy. 



The geometrical fundamental form of the lattice-shell in the Sphferellaria is 

 originally spherical (homaxon), as preserved in aU S p h se r o i d e a ; in the P r u n o i d e a 

 and D i s c i d e a it becomes monaxon, with one single axis (prolonged in the former, 

 shortened in the latter) ; in the L a r c o i d e a it becomes triaxon, by different growth 

 in three principal axes, perpendicular one to another. The further development of 

 radial parts of the skeleton in these three axes is very important for the " promorphology " 

 of the Radiolaria. 



The Mcdacoma, or the whole soft body of the Spumellaria as opposed to the skeleton, 

 exhibits some differences of structure in two different groups, which were separated 

 formerly (1862) as Monocyttaria and Polycyttaria, corresponding to the "Radiolaria 

 monozoa and polyzoa" of Johannes Midler (1858). 



The Monocyttaria (or the Spumellaria solitaria) live isolated as single cells — like 



