IX] OF THE NASSELLARIAN SKELETON 475 



of the system. Similar but more complex formations, all explicable 

 as basket-like frameworks developed around a cluster of cells, are 

 known in great variety. 



In our Nassellarian itself, and in many other cases where the 

 plane interfacial boundary- walls are skeletonised, we see that the 

 siliceous matter is not deposited in an even and continuous layer, 

 like the waxen walls of a bee's cell, but constitutes a meshwork 

 of fine curvilinear threads; and the curves seem to run. on the 

 whole, isogonally, and to form three main series, one approxi- 

 mately parallel to, or concentric with, the outer or free edge of 

 the partition, and the other two related severally to its two edges 

 of attachment. Sometimes (as may also be seen in our figure), 

 the system is still further complicated by a fourth series of linear 

 elements, which tend to run radially from the centre of the system 

 to the free edge of each partition. As regards the former, their 

 arrangement is such as would result if deposition or solidification 

 had proceeded in waves, starting independently from each of the 

 three boundaries of the little partition-wall ; and something of 

 this kind is doubtless what has happened. We are reminded at 

 once of the wave-like periodicity of the Liesegang phenomenon. 

 But apart from this we might conceive of other explanations. 

 For instance, the liquid film which originally constitutes the 

 partition must easily be thrown into vibrations, and (like the dust 

 upon a Chladni's plate) minute particles of matter in contact with 

 the film would tend to take up their position in a symmetrical 

 arrangement, in direct relation to the nodal points or lines of the 

 vibrating surface*. Some such explanation as this (to my thinking) 

 must be invoked to account for the minute and varied and very 

 beautiful patterns upon man}^ diatoms, the resemblance of which 

 patterns (in certain of their simpler cases) to the Chladni figures 

 is sometimes striking and obvious. But the many special pro- 

 blems which the diatom skeleton suggests I have not attempted 

 to consider. 



The last peculiarity of our Nassellarian lies in an apparent 

 departure from what we should at first expect in the way of its 



* Cf. Faraday's beautiful experiments, On the Moving Groups of Particles 

 found on Vibrating Elastic Surfaces, etc., Phil. Trans. 1831, p. 299; Besefircke-s 

 in Chem. and PJiys. 1859, pp. 314-358. 



