REPORT ON THE RADIOLARIA. iii 



monostatic or unistable, since the two poles of the principal axis are always more or 

 less different from each other. (5) The Ground-forms of the skeleton are, therefore, 

 for the most part grammotypic (centraxon) or zygotypic (centroplan), rarely spherotypic. 

 The two legions of the Osculosa are distinguished chiefly by the principal opening 

 (osculum) being closed by a porous plate (porochora with its podoconus) in the 

 Nassellaeia (or Monopylea), and by a radiate cover (operculum with its astropyle) in 

 the Ph^odaria (or Cannopylea). 



5. The four Legions of Radiolaria. — The four principal groups of Eadiolaria, to which 

 we have given the name " legions," are natural units, since the most important j)eculi- 

 arities in the structure of the central capsule are quite constant within the limits of the 

 same legion, and since all the forms in the same legion may be traced without violence 

 to the same phylogenetic stem. The four legions are, however, related to each other, in 

 so far as they all exhibit those characters which distinguish the Eadiolaria from other 

 Protista. The two which compose the Porulosa (§3) seem somewhat more nearly related 

 to each other than to the two which make up the Osculosa (§ 4). When, however, the 

 attempt is made to bring them all into a phylogenetic relationship, it undoubtedly apjaears 

 that the Spumellaria (or Peripylea) are the primitive stem, out of which the other three 

 have been developed as independent branches. All three have been derived, probably 

 independently, from the most ancient stem-form of the Spumellaria, the spherical Actissa. 



6. Perijjylea 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 di\'ides 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 Pseudo2)odia are exceedingly numerous and distributed 

 evenly over the whole surface of the central capsule. (4) The Calymma contains no 

 phseodium. (5) The Skeleton is seldom wanting, is never centrogenous, and is always 

 sihceous. (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 

 difiierent ways from the sphere. 



7. Actipylea or Acantharia. — Those Eadioloria 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 



