706 ON CONCRETIONS, SPICULES, [ch. 



beautiful artificial Rhizopod-shell is formed, but it takes some three 

 hours to do. Where the action is quick the Uttle test forms as the 

 droplet exudes from the pipette : precisely as in the living Difflugia 

 when new protoplasm, laden with soHd particles, is being extruded 

 from the mouth of the parent-cell. The experiment can be varied, 

 simply and easily. Instead of a spherical drop a pear-shaped one 

 may easily be formed, so exactly like the common Difflugia pyriformis 

 that -Rhumbler himself was unable, sometimes, to tell under the 

 microscope the real from the artefact. Again he found that, when 

 the alcohol dissolved the oily substance of the (^rop and shrinkage 

 took place accordingly, the surface-layer with its solid particles got 

 kinked or folded in — and reproduced in doing so, with startUng 

 accuracy, a httle shell of common occurrence, known by the generic 

 name of Lesqueureusia, or Diffiugia spiralis. The pecuhar shape 

 of this little twisted and bulging shell has been taken to shew that 

 "it had enlarged after its first formation, a very rare occurrence in this 

 group*"; the very opposite is the case. Neither here nor in any. 

 allied form does the agglutinated test, once set in order by capillary 

 forces, yield scope for intercalation and enlargement. 



At the very tinje when Rhumbler was thus demonstrating the 

 physical nature of the Difflugian shell, Verworn, a very notable 

 person, was studying the same and kindred organisms from the 

 older standpoint of an incipient psychology!. But as Rhumbler 

 himself admits, Verworn (unlike many another) was doing his best 

 not to over-estimate the appearance of vohtion, or selective choice, 

 in the little organism's use of materials to construct its dweUing. 



This long parenthesis has led us away, for the time being, from 

 the subject of the radiolarian skeleton, and to that subject we must 

 now return. Leaving aside, then, the loose and scattered spicules, 

 which we Have sufficiently discussed, the more perfect radiolarian 

 skeletons consist of a continuous and regular structure; and the 

 sihceous (or other inorganic) material of which this framework is 

 composed tends to be deposited in one or other of two ways or in 

 both combined: (1) in long radial spicules, emanating symmetrically 

 from, and usually conjoined at, the centre of the protoplasmic body; 



* Cf. Cambridge Natural History, Protozoa, p. 55. 



t Max Verworn, Psycho -physiologische Protisten-Studien, Jena, 1889 (219 pp.); 

 Biologische Protisten-Studien, Z. f. wiss. Z. L, pp. 445-467, 1890. 



