1536 THE VOYAGE OF H.M.S. CHALLENGER. 



A great part of the PH^ODARIA, and usually the bigger forms of Aulacanthida, Cannor- 

 rhaphida, Coelodendrida, Coelographida, &c., exhibit a peculiar structure of the larger 

 phseodella, viz., a fine parallel striation (PL 101, figs. 3, 6 ; PI. 102, fig. 1 ; 

 PI. 103, fig. 1 ; PI. 104, figs. 13, &c.). In each phseodellum may be counted 

 about ten to twenty such fine parallel stripes (more in the greater, less in the 

 smaller forms) ; and in the ellipsoidal phasodella the stripes are either transverse 

 rings, perpendicular to their main axis, or ascending obliquely ; they often resemble 

 the convoluted spiral filament of a thread-cell or nettle-cell of an Acaleph. Some- 

 times these parallel transverse stripes are very striking. Another structure is seen 

 in larger phseodella, namely an aggregate or cluster of smaller globules, often of equal 

 size, resembling a small morula. All these minute structures of the phseodella as 

 well as their changes in the living PH^EODARIA, require a far more extensive examina- 

 tion (by means of strong lenses and different chemical reagents), than I could, 

 unfortunately, devote to them. 



The physiological signification of the phseodella, therefore, is at present not yet 

 known ; but the general facts quoted above, their constant presence, position, volume, 

 and composition, make it probable that their physiological value in the PH^ODARIAN 

 organism is very great. The following hypotheses may be taken provisionally into 

 consideration : A. The phseodella are peculiar symbiontes, or unicellular algse, compar- 

 able to the xanthellse or zooxanthellse of the other Radiolaria. This hypothesis is pro- 

 bably correct for those phseodella which are true nucleated cells ; and the more so, as the 

 majority of PH^EODARIA do not exhibit those common yellow xanthellse, which are 

 usually found in the SPUMELLARIA and NASSELLARIA. It is even possible that the latter 

 are absent in all PHJEODARIA. B. The phseodella are dark pigment-bodies, which absorb 

 light and heat in a manner similar to the simple " pigment-eyes" of many lower animals, 

 and may therefore be optical sense-organs of the PHJEODARIA. This hypothesis may be 

 supported by a comparison with the large -eyed unicellular Protist, Erythropsis agilis, 

 described by R. Hertwig. C. The phseodella are organs of nutrition of the PH^ODARIA 

 and active in their metastasis (" Stoffwechsel "). Regarding them from this point of 

 view, we may suppose that the phseodella are secreted products which serve for digestion, 

 acting like the bile or the saliva of higher animals. Perhaps they too act like the 

 venomous matter produced in the thread-capsules of the Acalephse. The suggestion 

 that they are mere excretions, or half-digested matters, as Hertwig supposes (" halb 

 assimilirte Nahrungs-bestandtheile," 1879, loc. cit., p. 99) seems less probable. The 

 most important fact illustrating their high signification for the processes of nutrition, 

 digestion and for effecting changes on matter, seems to be the close relation of the 

 phseodium to the astropyle ; the radiate operculum of the latter, and the proboscis 

 arising from it, being constantly covered and completely hidden by the central main 

 mass of the phseodium. 



