The central capsule of the SPUMELLARIA, with its innumerable fine and evenly distributed pores, must be regarded as the primitive arrangement, from which the different central capsules of the three other legions have been developed. The central capsule of the ACTIPYLEA has been derived from that of the PERIPYLEA by reduction in the number of the pores and their distribution in definite, regularly disposed areas in the membrane. The central capsule of the Osculosa is characterised by the formation of a special main-aperture (osculum) at the basal pole, which is closed in the MONOPYLEA by the porochora, and in the CANNOPYLEA by the astropyle; the remaining pores, with the exception of the accessory openings of many CANNOPYLEA, remain undeveloped in both these legions. In the same way Hertwig regards the central capsule of the PERIPYLEA as the primitive form (1879, L. N. 33, p. 107). 58. _The Capsule-Openings of the Actipylea (or Acantharia)._--The capsule-membrane of the ACTIPYLEA is perforated by very numerous fine pores, which are regularly distributed over the surface of the central capsule, and separated by imporous intervals. Hence the ACANTHARIA belong to the "Holotrypasta" or "Porulosa"; they have neither osculum nor operculum, and agree in this particular with the PERIPYLEA; but they are separated from these latter chiefly by the fact that their pores are much less numerous, and marked off into regularly arranged groups or lines by imporous intervals. In the PERIPYLEA, on the contrary, the pores are much more numerous and are evenly distributed over the whole surface of the capsule. {xxx}The central capsule of the ACANTHARIA has hitherto been for the most part confounded with that of the SPUMELLARIA, and no clear distinction has been drawn in this respect between the two legions of the Porulosa. Hertwig, who in 1879 first discovered the remarkably different structure of the Osculosa (NASSELLARIA and PHÆODARIA), recognised no distinction between the structure of the capsules in the PERIPYLEA and ACTIPYLEA (his Acanthometrea), and supposed that in both these legions "very fine pores were evenly distributed in large numbers over the capsule-membrane" (_loc. cit._, p. 106). I have, however, during the last few years convinced myself, by the careful comparative investigation of numerous ACANTHARIA, that in this respect they are quite distinct from the SPUMELLARIA (with perhaps the exception of the Astrolophida, which are nearly related to the primitive _Actissa_). The number of pores in the ACTIPYLEA is usually very much smaller than in the PERIPYLEA, and they are regularly arranged in groups.