REPORT ON THE RADIOLARIA. Ixi 



of the calymma approaches that of cartilage, the tracks of the exoplasmic threads 

 remain constant, but accurate observations are wanting as to how far the configuration 

 of the sarcoplegma is constant or variable in the different groups, as well as regarding 

 its peculiar behaviour in those Radiolaria whose calymma is characterised by the 

 formation of vacuoles or alveoles (see 86). Usually it envelops the larger alveoles in 

 the form of a reticulate veil. In many Collodaria the exoplasm is aggregated at 

 certain points of the intracalymmar web, so that large balls or amoaboid bodies appear 

 to be distributed between the alveoles, e.g., in Thalassophysa pelagica and Thalassicolla 

 melacapsa (PI. 1, figs. 4, 5). The sarcoplegma is metamorphosed directly into silex 

 in the Radiolaria spongiosa, or those genera which possess a spongy cortical skeleton, 

 and were formerly known as Spongurida ; to this category belong the Spongosphserida 

 (PI. 18) and Spongodiscida (PI. 47) as well as certain NASSELLARIA and PH^ODARIA. 

 The single siliceous spicules, which are irregularly interwoven to form the spongy 

 web, are to be regarded as the silicified threads of the intracalymmar sarcode network. 

 From a physiological point of view the sarcoplegma is of importance both for the 

 nutrition and motion of the Radiolaria, since it brings the sarcomatrix and the sarco- 

 dictyum, with the pseudopodia which radiate from it, into direct communication. 



94. The Sarcodictyum. The sarcodictyum may be defined as the extracalymmar 

 network of exoplasm, and is a reticular covering which lies upon the outer surface 

 of the gelatinous calymma. Internally, the sarcodictyum is in direct communication 

 with the sarcoplegma, or the web of exoplasmic threads which ramifies in the gelatinous 

 substance of the calymma ; externally, on the other hand, the pseudopodia radiate freely 

 from it ; thus its relation to these is similar to that which the sarcomatrix bears to the 

 roots of the sarcoplegma. Relations similar to those which have led to the separation 

 of the primary from the secondary calymma, induce us to distinguish also a primary 

 and secondary sarcodictyum. The original or primary sarcodictyum ramifies over the 

 surface of the original or primary calymma, and like this is of pre-eminent importance 

 in the formation of the primary lattice-shell ; if we regard the surface of the primary 

 calymma as the indispensable foundation for the deposition of this latter, then the 

 primary sarcodictyum furnishes the material from which it is developed : silex in the 

 SPUMELLARIA and NASSELLARIA, a silicate of carbon in the PH^ODARIA, and acanthin in 

 the ACANTHARIA. It may indeed be said that the primary lattice-shell of the Radiolaria 

 arises by a direct chemical metamorphosis of the primary sarcodictyum, by a chemical 

 precipitation of the dissolved skeletal material (silex, silicate, or acanthin), which was 

 stored up in the exoplasm of the sarcodictyum. Hence a deduction from the special 

 conformation of the former to that of the latter is permissible. The particular form 

 of the primary lattice-sphere with its regular or irregular meshes is due to the corre- 

 sponding form of the primary sarcodictyum ; both regular and irregular forms of this 



