heport on the radiolaria. 1535 



ill the two plia30capsa3, which are composed of the two galeae (g), and the two 

 rhinocauna3 arisiug from them (PL 127, figs. 4—9). A part of the phaeodella is 

 usually thrown out by the mouth of the latter (?»-). 



The characteristic colour of the phseodium exhibits numerous different tints between 

 green, brown, and black. It seems to be in the majority blackish-brown or greenish- 

 brown, very often olive, more rarely almost quite green or red-browTi. Usually the 

 colour is so dark, intense and opaque, that the parts enclosed by the pha^odium, 

 mainly the oral hemisphere of the central capsule and the astropyle, are completely 

 hidden in it. The chemical composition of the phajodium demands further accurate 

 researches ; unfortunately I have not been able to make out its true nature, since 

 numerous different experiments furnished no certain general results. 



The pha3odella, or the pigment-corpuscles, which compose the phseodium, aggre- 

 gated in huudi'eds, and in the bigger species in thousands, are usually spherical, some- 

 times somewhat ellipsoidal, at other times spheroidal or lenticular ; but usually 

 numerous smaller, ii-regular, roundish particles are intermingled between the larger and 

 more regular corpuscles, and often the main mass forms a very fine black powder. 

 The size of the phaeodella is very variable, not only in the different species, but also in 

 one and the same individual. The larger phseodella have a diameter of O'Ol to 0'02, 

 the smaller of 0'004 to 0"008 mm. ; but there also occur very big forms of 0'04 to 0"05 

 mm., or even more, and very small ones of O'OOl mm. or less. Usually the phseodium 

 appears as an aggregate of numerous larger and smaller phseodella, which are very 

 different in size as well as in the intensity and tint of their colour, and are irregularly 

 crowded in a black, powder-like substance. 



The morphological nature of the phaeodella is also difficult to make out. I have 

 already pointed out in my first description of Aulacantha, Tlialassoj^lancta and 

 Coelodendrum (1862, loc. cit.), that a great part of these pigment-corpuscles are true 

 cells, composed of a nucleus and protoplasm, which contains granules of pigment, 

 and is enveloped by a membrane. Dr. John Murray, who had during the Challenger 

 voyage the opportunity of examining numerous different living Ph^odaria, and staining 

 them by carmine, also asserts that a great part of those dark corpuscles are " large 

 black -brown pigment-cells" (1876, loc. cit., p. 536). Numerous preparations of the 

 Challenger collection, well preserved in glycerine, and stained by carmine, contain 

 Ph^odakia belonging to different families, the phasodium of which contains numerous 

 such " pigment-cells," with a dark red nucleus, and so similar are these cells, that every 

 histologist should recognise them. But in strange contrast to this is the fact, that in 

 numerous other mountings, prepared in the same manner, not a single cell of this 

 kind is found in the phaeodium, and that the latter is composed only of iiTegular 

 pigment-granules. In many Ph^odaria belonging to different families I, like Hertwig, 

 could not find a single true nucleated cell in the phseodium. 



