REPORT ON THE RADIOLARIA. XXVU 



I. Spumellaria. — (A) In many of the Sph seroidea, the central capsule of which 

 is originally enclosed by a simple lattice-sphere, it puts out protrusions through 

 the meshes of the shell, thus forming club-shaped processes, corresponding in 

 number with the meshes of the lattice (PL 11, figs. 1, 5; PL 20, fig. la; 

 PL 27, fig. 3, &c.). The whole surface of the spherical capsule may thus be 

 covered with numerous independent radial clubs of equal size, but usually they 

 unite again outside the shell to form a simple sphere with smooth surface. 

 (B) In many Prunoidea whose originally ellipsoidal body has become 

 cylindrical by the marked prolongation of the main axis, the central capsule is 

 divided by a series of constrictions into segments, which correspond with the 

 annular constrictions of the skeleton (Pis. 39, 40). (C) In most D i s c o i d e a 

 whose lentiform or discoidal shell develops radial arms at its margin, the 

 central capsule sends out processes into these arms, and adapts itself to the 

 stellate form of the skeleton (p. 409, PL 43, fig. 15; PL 47, &c.) (D) In 

 many Larcoidea whose growth is originally lenteUiptical, but later spiral 

 or irregular, the central capsule follows the mode of growth and develops 

 irregular protuberances. 



II. AcANTHARiA. — Whilst the central capsule of most Acantharia retains its primi- 

 tive spherical form, in a minority of the group it passes over into various 

 secondary forms, which are directly determined by the growth of the skeleton ; 

 especially common are lappet or club-shaped prominences which follow the 

 larger radial spines. Hence the central capsule may assume the form of a 

 violin, with two lobes corresponding to the two poles of the elongated main 

 axis, as in many Amphilonchida (p. 782, PL 132, fig. 10), and the Diploconida 

 (p. 884, PL 140). On the other hand the central capsule becomes cruciform, 

 with four lobes disposed at right angles, as in Lithoptera and other Quadri- 

 lonchida (p 768, PL 131, fig. 10, &c.). 



III. Nassellaria. — The primitive ellipsoid or ovoid form of the central capsule 

 persists only in a few Nassellaria, such as the simplest and most archaic 

 forms, the Nassellida, many Plectoidea, Stephoidea, Monocyrtida, &c. 

 In the great majority of the Nassellaria, on the contrary, the ellipsoid or 

 ovoid form passes over into a secondary form which is usually characterised 

 by the presence of lobes, and is obviously dependent upon the previous 

 development of the skeleton. In many Stephoidea and S p y r o i d e a 

 (probably the majority), a bilobed central capsule is formed (with symmetrically 

 equal right and left lobes), since the primary vertical sagittal ring interferes 

 with the growth in the median plane (PL 90, figs. 7-10). In other 



