882 THE ANIMAL KINGDOM. 



in such quantity that it becomes deformed, the soft jelly being drawn out 

 into arms by the weight. It was in this state supposed to be a distinct 

 genus, Myxobrachia. 



The Radiolaria are found in all seas and in every latitude ; their wide 

 distribution is due to oceanic currents. The variety of species is greatest 

 in tropical regions. The Pacific Ocean has an extremely rich fauna, both 

 in species and numbers, and is probably closely approached by the Indian 

 Ocean. They are found at all depths, pelagic, i. e. at or near the surface, 

 zonarial and abyssal. The Spumettaria and Acantharia predominate at 

 the surface, the Nassellaria and Phaeodaria at abyssal depths ; the zonarial 

 fauna being a mixed one. It is probable that the young of a given species 

 are found at a greater depth than the adult. The organic skeletons of 

 Acantharia perish at death, but the siliceous skeletons of Sptimellaria and 

 Nassellaria (=Polycystina of Ehrenberg), and of Phaeodaria, to a very 

 slight extent, occur in marine deposits. They make up often more than 

 three-quarters of the Radiolarian ooze which has been dredged in the 

 Pacific and Indian Oceans at depths of 2-3000 fathoms. In Globigerina 

 ooze (p. 893 post) they are frequently present in great numbers. Nor are 

 they wanting in the deepest and most extensive of oceanic deposits, the 

 Red Clay, which is probably derived to a great extent from the decom- 

 position of their shells. They are also found in varying proportions in 

 muds near the shores. The same groups occur fossil, the Phaeodaria 

 being represented by the family Dictyochida, which has a perfectly solidi- 

 fied skeleton. Simple SpumeUaria and Nassellaria have been detected in 

 various Palaeozoic strata. Among Mesozoic formations they are found 

 principally in Jurassic strata, in quartzites of various kinds (fossilised 

 Radiolarian ooze) and in coprolites, scantily in the Chalk and Trias. The 

 Spumellarian Sphaeroida and Discoidea constitute the minority, the Nas- 

 sellarian Cyrtoidea the majority ; the skeletons are simple and massive, 

 somewhat larger than the Radiolaria of the Tertiary strata. The deposits 

 of the latter are apparently of Miocene age, and contain either living species 

 or species akin to them. They are found plentifully in Barbados as marls, 

 sometimes almost pure Radiolarian ooze, sometimes Globigerina ooze, or 

 containing clay, pumice, &c. ; in the Nicobar Islands as a Radiolarian clay ; 

 and in the Mediterranean round its coasts, both South European and North 

 African (Oran to Tripoli), and in its islands, as marls, chalky deposits, 

 powdery tripoli, sometimes coherent as whetstone or polishing slate. 



Haeckel classifies the Radiolaria as follows : 



A. Holotrypasta s. Porulosa : central capsule with innumerable fine pores : sphe- 

 rical or derived from a sphere. 



I. SpumeUaria s. Peripylea : pores of capsule evenly distributed; skeleton 

 siliceous or wanting ; contains (i) Collodaria, with no skeleton, Colloidea, e. g. 

 Thalassicolla, Collozoum, or a spicular skeleton, Beloidea, e. g. Physematium, Sphae- 



