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



commonly occurring. The form of the regular sarcodictyum with circular or regular 

 polygonal, usually hexagonal, meshes is constantly maintained during the formation of 

 the regular lattice-shells (e.g., PI. 12, figs. 5-10 ; PL 52, figs. 8-20 ; PI. 96, figs. 2-6 ; 

 PI. 113, figs. 1-6). The form of the irregular sarcodictyum, on the other hand, 

 with irregular polygonal or roundish meshes, persists during the development of the 

 irregular lattice-shells (e.g., Pis. 29, 70, 97, 106). All this is true also of the 

 secondary sarcodictyum, or the exoplasmic network which ramifies over the surface of the 

 secondary calymma. The secondary lattice-shells, which are deposited on the surface of 

 the latter, retain the configuration of the secondary sarcodictyum, by the chemical 

 metamorphosis of which they have originated ; this is the case in many SPUMELLAEIA 

 which develop several concentric lattice-shells (PL 29), in some NASSELLARIA (PL 54, 

 fig. 5), in the Phractopeltida among the ACANTHAKIA (PL 133), and in the double- 

 shelled PH^EODARIA, Cannosphserida, and part of the Ccelodendrida and Coelographida 

 (Pis. 112, 121, 128). In those Radiolaria which form no lattice-shell whatever, the 

 conformation of the sarcodictyum is usually irregular, with meshes of irregular form 

 and unequal size ; sometimes, however, they seem to be very regular, as in many 

 Acanthometra (PL 129, fig. 4). 



95. The Pseudopodia. On the whole the pseudopodia or thread-like processes of the 

 exoplasm exhibit in the Radiolaria the same characteristic peculiarities as in all true 

 Rhizopoda ; they are usually very numerous, long and thin, flexible and sensitive 

 filaments of sarcode, which show the peculiar phenomena of granular movement. Their 

 physiological significance is in several respects very great, for they serve as active organs 

 for the inception of nutriment, for locomotion, sensation, and the formation of the skeleton 

 (see note A, below). The presence of a calymma, however, which distinguishes the 

 Radiolaria from the other Rhizopoda, brings about certain modifications in the behaviour 

 of the pseudopodia. If in general all the threads, which arise from the sarcomatrix or 

 fundamental layer and radiate outwards, be called " pseudopodia," then that part of them 

 which is included in the gelatinous substance of the calymma and forms the sarcoplegma 

 may be termed the " collopodia " (or intracalymmar pseudopodia), and the remaining 

 portion, which passes outwards from the sarcodictyum freely into the water, may be 

 described as " astropodia " (or extracalymmar pseudopodia). In many Radiolaria these 

 two portions present some differences in morphological and physiological respects, and 

 certain distinctions are probably generally present (see note B). Apart from this universal 

 differentiation in the different groups of the Radiolaria, specially modified forms of 

 pseudopodia may be recognised as the axopodia and myxopodia of the ACANTHARIA (see 

 95, A), and the sarcode-flagellum of certain SPUMELLARIA (see note C). 



A. The pseudopodia of the Eadiolaria have been so fully described in my Monograph, in 1862, 

 both morphologically and physiologically, that I need only refer to the account there given 



