42 PROTOZOA— RHIZOPODA phylum i 



more nuclei, vacuoles, alveoles, granules, oil- globales and sometimes crystals 

 and surrounded by a capsule-membrane perforated by pores or pylae ; and 

 (2) an outer jelly-like extra-capsulum, the sarcode of which emits pseudopodia. 

 The individuals lead usually an isolated existence, and are only rarely united 

 in colonies. 



Most Radiolarians secrete skeletons composed of either bars or spicules of 

 acanthine (an organic substance allied to hörn or chitin) or silica, or they build 

 an exceedingly delicate lattice-work composed of transparent amorphous silica. 

 Only the latter forms are known in a fossil State, and owing to their minute 

 size, are commonly indiscernible except with the aid of the microscope. 



Haeckel divides the Radiolaria into four suborders, as follows : — 



A. Acantharia. — Capsule-membrane uniformly perforated ; skeleton com- 

 posed of acanthinic spicules. Unknown in fossil State. 



B. Spumellaria. — Capsule-membrane single, pores distributed all over; 

 skeleton siliceous, spherical or discoidal, sometimes wanting (Fig. 43). 



Fig. 41. 

 Silurian and Devonian Radiolarians : A, Cenosphaera macropora Rüst. Ordovician ; Cabrieres, Langnedoc. 

 B, Staurolo)iche micropora, Rüst. Ordovician ; Cabrieres. C, Caryosphaera groddecJd Rüst. Upper Devonian ; 

 Schäbenholz, near Elbingerode, Harz Mountains. D, Lithocampe tschernytscJie%ni Rüst. Devonian ; Ural. 

 Magnifted 100 to 120 diameters (after Rüst). 



C. Nasselaria. — Capsule-membrane single, perforated only about the otäl 

 pole ; skeleton siliceous, helmet- or cap-shaped, conformation of poles dissimilar 

 (Figs. 44, 45). 



D. Phaeodaria. — Capsule-membrane double, perforated by one main opening 

 prolonged into a tubulus, and by a few smaller accessory openings. A dark 

 pigment body (phaeodium) constantly present in extra-capsular sarcode. Skeleton 

 commonly consisting of hollow siliceous spicules disposed in flask-shaped or 

 variously shaped frameworks. Unknown in fossil state. 



Radiolarians are exclusively marine organisms, and are found at all bathy- 

 metric zones. They occur in vast numbers, especially in tropical seas, 

 swimming on the surface, as well as at medium and even abysmal depths. 

 Particularly between 2000 and 4000 fathoms in depth, extensive deposits of 

 " Radiolarian mud " have been found, the composition of which is largely silica 

 with a small percentage of carbonate of lime. 



Organismus der Radiolarien. Jenaische Denkschr., 1879, vol. ii. — Stöhr, E., Die Eadiolarien- Fauna 

 von Grotte in Sicilien. Palaeoutogr., 1880, vol. xxvi, — Rüst, D., Radiolarien aus Gesteinen des 

 Jura. Palaeontogr., 1885, vol. xxxi. — Idem, op. cit., vols. xxxiv. xxxviii. and Iv. — Dreyer, F., Die 

 Tripoli von Caltanisetta. Jenaisclie Zeitsclir. f. Naturw., 1890, vol. xxiv. — Cayeux, Z., Les Preuves de 

 l'existence d'organismes dans le Precambrien. Bull. Soc. Geol. France, 1894, vol. xxii. — Vinassa 

 de Regny, P. E., Radiolarie delle flaniti titoniane di Carpena (Spezia). Palaeont. Italica, 1899, vol. 

 iv. — Hinde, G. J., Radiolaria in Devonian Rocks of New South Wales. Quart. Journ. Geol. Soc, 

 London, 1899, vol. \v.—Ideni, Radiolaria from the Triassic of the Dutch Fast India Archipelago. 

 Jaarb. Mijnwezen Nederl. Ooost India, 1908, vol. xxxvii. — Squinabol, S., Radiolarie cretacee degli 

 Euganee. Padova, 1904. — Principi, P., Contributo allo studio dei radiolari miocenici italiani. 

 Boll. Soc. Geol. Ital., 1910, vol. xxviii. 



