1898.] on Living Crystals. 720 



a remarkable series of events takes place. First, three cells come 

 together and form a triradiate system in the usual way. Then a 

 cell is given oif by the division of the nearest pore cell, and this 

 cell travels to the little triradiate spicule and takes up a position 

 over it, on its inner side. Then the cell secretes a little rod of 

 calcite, which is stuck on to the triradiate system, converting it into 

 a four-rayed spicule, so that not only is the fourth ray a late addition 

 to the basal system, but it is derived from quite a different source, 

 the basal rays being formed by cells of one class, the fourth ray by 

 a cell of a different class. The development of the triradiate and 

 quadriradiate spicules shows them, in fact, to be composite bodies, 

 built up of a number of skeletal elements, each a simple rod. This 

 is remarkable, and even paradoxical, in view of the fact already men- 

 tioned, that each spicule, when full grown, is a single crystal. In 

 their earliest stages, however, it is found that the minute triradiate 

 systems are at first non-crystalline, and only become so after the 

 rays have been joined together. Then, since all parts are in con- 

 tinuity, the crystallisation takes place in such a way that all parts 

 of the spicule have a uniform molecular arrangement, producing not 

 three or four separate crystals, as might at first sight have been 

 expected, but a single one. 



It is seen, therefore, that the primitive skeletal element in Ascons 

 is a simple rod, and that the general course of evolution was such as 

 has been traced out, some rods remaining single but growing out from 

 the surface ; others becoming arranged in trios and forming triradiate 

 systems ; and others, again, becoming tacked on to the triradiates to 

 form the four-rayed spicules. But how did the primitive skeletal 

 elements, the rods, themselves originate ? Unless an intelligible origin 

 can be suggested for them, there is a gap in the scheme of evolution. 

 Now any living organism, however simple, is composed of matter 

 which is in process of constant change and transmutation. As a 

 result of metabolism, substances of all kinds are continually being 

 formed, and amongst them many of crystalline nature, which may be 

 deposited from a state of solution and crystallise out. Hence it is 

 not uncommon to find ordinary crystals in living tissues, crystals 

 which show no sign of having any origin at all out of the common, 

 and which must be supposed either to be of no use to the organism 

 that produced them, or at least to perform some function for which 

 their external form is not of great importance. It is a rational sup- 

 position, therefore, that the spicules of Ascons also had at one time the 

 form as well as the constitution of crystals, and originated simply as 

 bye-products, so to speak, of the wear and tear of the living substance. 

 When, however, it became of importance to the organism that they 

 should have one form rather than another, then their natural form 

 became modified and completely altered. Now this is the most 

 obscure portion of all their history, how, namely, the living substance 

 can so act upon the growing crystal as to cause it to assume a form 



