REPORT ON THE RADIOLARIA. Ixix 



whose skeleton is made up of isolated scattered tangential siliceous fragments). The 

 enormous deposits of Radiolarian skeletons in the deep sea of to-day, which constitute 

 the Radiolarian ooze, consist, like the fossil Polycystine marls, almost exclusively of the 

 shells of SPUMELLARIA and NASSELLARIA, though here the acanthin skeletons of the 

 ACANTHARIA may be present in very small numbers, and the silicate skeletons of the 

 PELEODARIA, which offer more resistance to the solvent action of sea- water, somewhat 

 more abundantly. Calcareous skeletons do not occur in the Radiolaria (see note D). 



A. The pure siliceous skeletons of the Polycystina were first recognised in 1838 by Ehrenberg 

 in chalky marls (L. K 2, p. 117). Since the two legions ACANTHARIA and PH.EODARIA were 

 entirely unknown to Ehrenberg, his name Polycystina has reference only to the SPUMELLAEIA and 

 NASSELLARIA. 



B. The silicate skeleton of the PH^ODARIA was formerly taken by me for a purely siliceous one. 

 When I described the first PH^EODARIA in my Monograph in 1862, I was only acquainted with five 

 genera and seven species, whilst the number of PH^EODARIA here described from the Challenger 

 amounts to eighty-four genera and four hundred and sixty-five species. In the great majority of 

 these (though not in all) the skeleton becomes more or less intensely stained by carmine, and is 

 also more or less charred at a red heat, in some even becoming of a blackish-brown. In many 

 PH^ODARIA, furthermore, the hollow skeletal tubes are destroyed by the continued action of heat. 

 They are also, for the most part, strongly acted upon, or even destroyed by boiling caustic alkalis, 

 whilst boiling mineral acids have no effect upon them. The best method of cleaning the skeletons 

 of PH^EODARIA from their soft parts is to heat them in concentrated sulphuric acid, and then add a 

 drop of fuming nitric acid ; in this they are not dissolved even on prolonged heating. From these 

 facts it would appear that the skeletons of the PH^ODARIA consist of a compound of organic 

 substance and silica, or a " carbonic silicate." The more intimate composition yet remains to be 

 discovered, as also the manifold differences which the various families of PILEODAHIA seem to show 

 in respect of its composition. The small skeletal fragments of the Dictyochida (the only remains 

 of PH^ODARIA which occur as fossils) appear to consist of pure silica. 



C. The acanthin skeleton of the ACANTHARIA was first described as such in. my Monograph 

 (1862, pp. 30-32). Johannes Miiller, the discoverer of this legion, took them for siliceous skeletons 

 and defined the Acanthometraas " Eadiolaria without lattice-shell, but with siliceous radial 

 spines " (L. N. 12, p. 46). I formerly supposed that the acanthin skeletons in some of the 

 ACANTHARIA were partially or wholly metamorphosed into siliceous skeletons, but, according to the 

 investigations of R Hertwig, this does not appear to be the case ; he showed that the skeletons of 

 the most varied Acanthometra and Acanthophracta are completely dissolved under 

 the longer or shorter action of acids, and supposes that in all ACANTHARIA, without exception, the 

 skeleton is composed of acanthin (1879, L. N. 33, p. 120). Quite recently Brandt has found that 

 the acanthin spines dissolve not only in acids, alkalis, and " liquor conservative " (as I had shown), 

 but also in solutions of carbonate of soda (1 per cent.), and even of common salt (10 to 20 per 

 cent.) ; he concludes from this that they consist of an albuminoid substance (vitellin) (L. N. 38, 

 p. 400). I am unable to share this view, for I have never been able to see some of the most 

 important reactions of albumen in any of the skeletons which I have examined, such for example 

 as the xanthoproteic reaction, the red coloration with Millon's test, &c. They do not become 



