222 



THE VOYAGE OF H.M.S. CHALLENGER. 



this outwards, from a thin layer of sarcode immediately surrounding the capsule. 

 Outside the gelatinous envelope the pseudopodia form a network, and show the same 

 granular movement as in other Rhizopoda, by means of which nutrition, locomotion, 

 and perception are carried on. Their extreme terminations are free radial threads. 

 Oil-globules, pigment-granules, vacuoles, &c, not unfrequently occur in the extra- 

 capsularium. 



" In many Radiolaria, but by no means in all, are found, in addition to these, scattered 

 round about the central capsule, numerous yellow cells, which contain starch. These 

 have been lately recognised as unicellular Algae (Zooxanthellce), which live in a state of 



symbiosis with the Eadiolaria, just 

 as do the Gonidia with the Lichens. 

 They also have an independent 

 power of reproduction. 



" The inner protoplasm, which is 

 enclosed in the central capsule, is in- 

 timately connected in two different 

 ways with the outer sarcode which 

 surrounds it. In the Holotrypasta 



Fig. 89. — Xiphacantha murrayaiut,, n. sp. 



-HP' 1 



Fig, 90. — Lilhoptera darwinii, n. sp. 



(Acantharia and Spumellaria) the membrane is everywhere perforated by numberless 

 small pores, through which the two communicate. In the Merotrypasta (Nassellaria 

 and Phaeodaria), on the contrary, there is only a single large opening in the capsule, 

 through which the pseudopodia protrude. There are, however^ not unfrequently found, 

 beside this, two or more small accessory openings. 



" The great majority of Radiolarians, with indeed few exceptions, are remarkable for 

 skeletons of the most varied and delicate forms. In one order (the Acantharia) these 

 consist of acanthin, a peculiar organic substance related to chitin ; in the other three 

 orders, on the contrary, of silica or an organic silicate. In the Phaeodaria the separate 

 siliceous portions which constitute the skeleton are, for the most part, hollow tubes, but 



