8 THE VOYAGE OF H.M.S. CHALLENGER. 



all other Radiolaria — and aie never aggregated in colonies ; tlie cal}Tnnia includes one 

 single central capsule, and this again one central nucleus, which does not become 

 divided until full maturity. 



The Polycyttaria on the contrary (or the Spumellaria socialia) live aggregated 

 in large colonies ; the calymma includes a variable number of associated central capsules 

 and each of these commonly one central oil-globule, whilst the original simple nucleus 

 commonly becomes very early divided into numerous small nuclei. 



The Nucleus of the Spumellaria is originally constantly central, j)laced quite in the 

 centre of the concentric capsule, and it retains this central position in aU Monocyttaria 

 or solitary Peripylea ; whereas in the Polycyttaria — in consequence of its early division — 

 its place is commonly taken by a central oU-globule. Whilst the numerous nuclei of the 

 latter are very small, the single nucleus of the former is comparatively large, extremely 

 large (more than a millimeter in diameter) in some gigantic Collodaria. 



The Endoplasm or the intracapsular sarcode exhibits in the greater number of 

 Spumellaria a more or less distinct radial striation. It encloses a great variety of 

 different parts ; vacuoles, oU-globules, pigment-granules, crystals, &c. 



The Membrane of the capsule in all Spumellaria is simple (never double as in the 

 Phceodaria) and everywhere equally perforated by innumerable small pores ; in the thick, 

 double-edged membrane of many large Collodaria these pores appear (in the optical 

 section of the caj)sule-wall) as distinct fine radial canals, very densely and regularly disposed. 



The Central Capsule in the Spumellaria is originally a geometrical sphere, and this 

 simple globular form is preserved in all Sphseroidea, and in the greatest part of 

 Colloid ea and Beloidea. By prolongation of one axis the form becomes 

 ellipsoidal (or even cyHndiical) in the P r u n o i d e a, and in some few forms of 

 Colloidea. By shortening of one axis it becomes lenticular (or even discoidal) in 

 the Discoidea, and in some few forms of Colloidea. By unequal growth in three 

 different axes, perpendicular one to another, the capsule becomes lentelliptical in all 

 L a r c o i d e a. Very rarely the capsule assumes in the Spumellaria a polyhedral or 

 irregular (sometimes even amoeboid) form, only in a few Colloidea. 



The Calymma, or the jelly- veil including the central capsule, is very voluminous in 

 many Spumellaria of gigantic size, mainly in the large Colloidea, and in aU Poly- 

 cyttaria or social Radiolaria. It includes here a considerable number of large vacuoles or 

 "alveoli." The calymma never exhibits in this legion the dark voluminous ph^odium, 

 possessed by all Ph^odaria. 



Xanthellce or " zooxantheUse " are numerous in the calymma of most Spumellaria, 

 but by no means constant ; they are very variable in number and size. 



The Matrix, placed between the cal}Tnma and central capsule, is, in the majority of 

 the Spumellaria, a rather thick layer of granular exoplasm. 



The Pseudopodia arising from it are very numerous, equally disj)Osed over the whole 



