RADIOLARIA. 883 



rozoum ; (ii) Sphaerellaria with a lattice or spongy shell always complete, spherical 

 in Sphaeroidea, which contains the colonial Collosphaerida among other forms, 

 cylindrical or elliptical in Prunoidea, discoidal in Discoidea, lent-elliptical in 

 Larcoidea. 



II. Acantharia s. Actipylea : pores in groups or lines, skeleton composed of 

 acanthin in the form of radial spines, with or without a lattice-shell ; contains (i) 

 Acanthometra with spines, lattice-shell if present incomplete, the former indefinite 

 in number and irregularly arranged in Actinelida, or twenty and regularly arranged 

 in Acanthonida ; (ii) Acanthophracta with twenty spines regularly arranged, and 

 complete lattice-shell ; subdivided according to character of shell and size of 

 spines. 



B. Merotrypasta s, Osculosa : central capsule with one principal aperture, and 

 with or without accessory openings ; derived from an egg-shape, or perhaps bilateral. 



III. Nassellaria s. Monopylea : a porous area = porochora at one pole of main 

 axis with an intracapsular podocone ; skeleton siliceous : contains (i) Plectellaria, 

 without shell, Nassoidea (Cystidium, Nassella\ or with an incomplete one, either a 

 basal tripod without ring, Plectoidea, or a sagittal ring usually without tripod, 

 Stephoidea (ii) Cyrtellaria, with a complete lattice-shell or cephalis, bilocular with 

 sagittal constriction, Spyroidea, multilocular with two or more constrictions and 

 lobes, Botryodea, or simple, Cyrtoidea. 



IV. Phaeodaria s. Cannopylea s. Pansolenia, including Tripylea of R. Hertwig ; 

 membrane of central capsule double ; an astropyle with or without parapylae ; a 

 phaeodium surrounding astropyle ; skeleton siliceous : contains (i) Phaeocystina, with 

 skeleton wanting, Phaeodinida (Phaeocolla, Phaeodina\ or composed of scattered 

 pieces, Cannorhaphida, or hollow radial tubes, Aulacanthida ; (ii) Phaeosphaeria, a 

 simple lattice-shell, or one of hollow tangential tubes with nodal septa, single or 

 double ; (iii) Phaeogromia, a simple spherical, ovate or polyhedral shell, with large 

 mouth opposite astropyle surrounded by teeth or feet, diatomaceous, Challengerida, 

 alveolate, Medusettida, latticed, Castanellida : or porcellanous with fine needles im- 

 bedded in a punctate cement, Circoporida, Tuscarorida ; (iv) Phaeoconchia, a 

 bivalved lattice-shell, thick and firm, Concharida, or thin, fragile, scarcely latticed, 

 with a conical cupola or helmet-shaped galea at the centre of each valve, and with 

 hollow tubes, Coelodendrida, Coelographida. 



The number of genera and species known is very large. 



Biitschli, Bronn's Klass. und Ordn. des Thierreichs, i. Protozoa, pp. 332-478 ; 

 Haeckel, 'Report on the Radiolaria,' Challenger Reports, xviii. 1887; Id. 'Die 

 Radiolarien,' Berlin, 1862; Brandt, 'Die Kolonie-bildende Radiolarien,' &c., Fauna 

 und Flora des Golfes von Neapel, xiii. 1885 ; R. Hertwig, 'Organismus der Radiola- 

 rien,' Dk. Med. Wiss. 'Ges. Jena, ii. 1880; Id. 'Zur Histologie der Radiolarien,' 

 Leipzig, 1876. 



Coelothamnus Davidoffii and structure of skeleton, especially in Cyrtida, 

 Biitschli, Z. W. Z. xxxvi. 1882 ; Thalassicolla coerulea, Eberth, A. M. A. xxx. (i), 

 1887. 



Extracapsular bodies ; spore-formation ; phosphorescence and other points of 

 physiology, Brandt, op. cit. supra. 



Regeneration from central capsule, Schneider, Archiv fur Anat. und Physiol. 

 1867, p. 509. 



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