6. _Peripylea or Spumellaria._--Those Radiolaria which we call "PERIPYLEA" on account of the constitution of their central capsule, or "SPUMELLARIA" on account of the nature of their skeleton, are separated from the other three legions of the class by the combination of the following constant characters:--(1) The _Membrane_ of the central capsule is single and evenly perforated all over by innumerable fine pore-canals, but without any larger principal opening (osculum). (2) The _Nucleus_ always lies centrally in the SPUMELLARIA monozoa and is serotinous, for it divides only at a later period into the nuclei of the spores; in the SPUMELLARIA polyzoa it is precocious, and divides early into many small nuclei. (3) The _Pseudopodia_ are exceedingly numerous and distributed evenly over the whole surface of the central capsule. (4) The _Calymma_ contains no phæodium. (5) The _Skeleton_ is seldom wanting, is never centrogenous, and is always siliceous. (6) The _Ground-form_ of the central capsule is originally spherical (often modified); that of the skeleton is also spherical or, in the majority of cases, derived in different ways from the sphere. 7. _Actipylea or Acantharia._--These Radiolaria which we call "ACTIPYLEA" on account of the constitution of their central capsule, or "ACANTHARIA" from the formation of their skeleton, are separated from the other three legions by the combination of the following constant characters:--(1) The _Membrane_ of the central capsule is single and {iv}perforated by numerous fine pore-canals, which are regularly distributed in series or groups, but without a larger principal opening (osculum). (2) The _Nucleus_ is always excentric and generally precocious, since it divides early by a peculiar process of budding into numerous small nuclei. (3) The _Pseudopodia_ are very numerous and distributed regularly in groups (or series united into a network). (4) The _Calymma_ contains no phæodium. (5) The _Skeleton_ is generally present, always centrogenous, and composed of acanthin. (6) The _Ground-form_ of the central capsule is originally spherical (often modified), that of the skeleton polyaxon (often modified).