RADIOLARIA 



embedded in the ectoplasm of some of the Phaeocystina, and 

 have a skeleton of similar nature. Their true nature was shown 

 by Borgert. 



The Amphipod crustacean Hyperia 1 may enter the jelly of 

 the colonial forms, and feed there at will on the host. 2 



Haeckel, in his Monograph of the Eadiolaria of the Challenger 

 enumerated 739 genera, comprising 4318 species; and Dreyer has 

 added 6 new genera, comprising 39 species, besides 7 belonging to 

 known genera. Possibly, as we shall see, many of the species 

 may be mere states of growth, for it is impossible to study the life- 

 histories of this group ; on the other hand, it is pretty certain 

 that new forms are likely to be discovered and described. The 

 Eadiolaria are found living at all depths in the sea, by the 

 superficial or deep tow-net ; and some appear to live near the 

 bottom, where the durable forms of the whole range also settle 

 and accumulate. They thus form what is known as Eadiolarian 

 ooze, which is distinguished from other shallower deposits chiefly 

 through the disappearance by solution of all calcareous skeletons, 

 as they slowly fell through the waters whereon they originally 

 floated at the same time with the siliceous remains of the 

 Eadiolaria, The greatest wealth of forms is found in tropical 

 seas, though in some places in cold regions large numbers of 

 individuals of a limited range of species have been found. 



Eadiolaria of the groups with a pure siliceous skeleton can alone 

 be fossilised, even the impure siliceous skeleton of the Phaepdaria 

 readily dissolving in the depths at which they live : they have 

 been generally described by Ehrenberg's name Polycystineae. 

 Tripolis (Kieselguhr) of Tertiary ages have been found in many 

 parts of the globe, consisting largely or mainly of Eadiolaria, and 

 representing a Eadiolarian ooze. That of the Miocene of 

 Barbados contains at least 400 species; that of Gruppe at least 

 130. In Secondary and Palaeozoic rocks such oozes pass into 

 Eadiolarian quartzites (some as recent as the Jurassic). They 

 occur also in fossilised excrement (coprolites), and in Hint or 

 chert concretions, as far down as the lowest f ossiferous rocks, 



1 Brandt, "Die Koloniebildenden Radiolarien," in Fauna u. Flora des G 

 Neapcl, xiii. 1885, gives a full account of the Zooxanthellae and Diatoms, and notes 

 the parasitism of Hy})eria. 



2 See Kbppen in Zool. Anz. xvii. 1894, p. 417. For Sticholo^ 

 Hertwig in Jena. Zeitsch. xi. 1877, p. 324 : and Korotneff in Zeitsch. iciss. ZooL 

 li. 1891, p. 613. Borgert's paper on Dictyochidae is in the same volume, p. 629. 



