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



87. The Extracapsular Fat-Globules. — Fat is probably as widely distributed in 

 the exoplasm as in the endoplasm of the Radiolaria ; a considerable proportion of the 

 small, dark, highly refractive granules appear to consist of fat ; most likely they are 

 for the most part direct products of metastasis. These widely-spread granules, which 

 are sometimes coloured, and which by their passive motion produce the phenomenon of 

 granular circulation in the exoplasm, are not the only fatty structures in the extra- 

 capsulum; larger globules sometimes occur. In certain large Collodaria {e.g., 

 Thalassicolla melacapsa, PI. 1, fig. 5; Thalassophysa sanguinolenta, &c.) radial 

 series of oil -globules are found in the calymma, especially in its proximal portion; in 

 others the central capsule is surrounded by a layer of oil-globules (situated in the 

 sarcomatrix). In the Ph^odakia a part of the phseodium appears to consist of fat- 

 globules. 



88. TJie Extracapsular Pigment. — The formation of colouring matters in the 

 extracapsulum is on the whole rare in the Radiolaria, apart from the " yellow cells " 

 (see § 91) and from the peculiar phseodium of the PniEODARiA, which will be separately 

 treated of in the next paragraph. Considerable masses of extracapsular pigment, 

 usually black or blue, rarely brown or red, are found only in a few Radiolaria belonging 

 to the first three legions ; most often in the Spumellaria. Some large Collodaria, 

 e.g., the common Thalassicolla nucleata and a few other species of this genus (PL 1, 

 fig. 4), are characterised by a rich deposit of black or blue pigment in the sarcomatrix 

 and in the proximal portion of the calymma. Brown pigment is deposited in the 

 calymma of many Sphseroidea and Discoidea, as well as of some Nassellaeia 

 {Cystidium, Tridictyopus, &c.). In a part of the Acantharia red pigment granules 

 are thickly strewn in the sarcoplegma and pass along the free pseudopodia, as for 

 example in Actinelius purpureus and Acanthostaurus purpurascens. The composition 

 and significance of these extracapsular pigments are not completely known. 



On the extracapsular pigment of Thalassicolla nucleata, compare my Monograph, pp. 87, 25L 

 On the red extracapsular pigment-granules of the Acanthakia, see L. N. 19, pp. 345, 364, &c. 



89. The Phceodium of the Phceodaria. — The PniEODARiA, which are distinguished 

 from the other three legions of Radiolaria by the double membrane of the central 

 capsule, and the peculiar structure of the main-opening (astropyle), differ also in other 

 points, the most important of which is the constant presence of a voluminous mass of 

 extracapsular pigment. This possesses a peculiar constitution and special significance, 

 and is not to be confounded with the extracapsular pigment-granules of other Radiolaria 

 {e.g., TJialassicolla), and hence it has been distinguished by the name " Pha^odium," 

 and the individual granules which compose it as "Phseodella" (see note A). The 

 phseodium is always excentric in position relatively to the central capsule, of which it 



