426 



ON CONCRETIONS, SPICULES, ETC. 



[CH. 



dispersion medium). In accordance with a rule first recognised 

 by Ostwald*, when a substance begins to separate out from a 

 solution, so making its appearance as a new phase, it always 

 makes its appearance first as a liquid |. Here is a case in point. 

 The minute quantities of material, on their way from a state of 

 solution to a state of "suspension," pass through a liquid to a 

 solid form ; and their temporary sojourn in the former leaves its 

 impress in the rounded contours which surface-tension brought 

 about while the little aggregate was still labile or fluid : while 

 coincidently with this surface-tension effect upon the surface, 

 crystallisation tended to take place throughout the little liquid 

 mass, or in such portion of it as had not yet consolidated and 

 crystallised. 



(After Harting.) 



Where we have simple aggregates of two or three calcospherites, 

 the resulting figure is precisely that of so many contiguous soap- 

 bubbles. In other cases, composite forms result which are not 

 so easily explained, but which, if we could only account for them, 

 would be of very great interest to the biologist. For instance, 

 when smaller calcospheres seem, as it were, to invade the substance 

 of a larger one, we get curious conformations which in the closest 

 possible way resemble the outlines of certain of the Diatoms 

 (Fig. 203). Another very curious formation, which Harting calls 

 a "conostat," is of frequent occurrence, and in it we see at least 

 a suggestion of analogy with the configuration which, in a proto- 

 plasmic structure, we have spoken of as a "collar-cell." The 



* Of. Taylor's Chemistry of Colloids, p. 18, etc., 191.5. 



•j- This rule, undreamed of by Errera, supports and justifies the cardinal 

 assumption (of which we have had so much to «ay in discussing the forms of cells 

 and tissues) that the incipient cell-wall behaves as, and indeed actually is, a liquid 

 film (cf. p. 306). 



