FORMS OF SPICULES. 69 



amorphous deposits are undoubtedly colloidal media/ and, 

 since complex shapes produced by colloidal media are almost 

 always characterised by the possession of curved surfaces, 

 and thus, though connected by all transitional forms with 

 those of simple crystals, constitute a class of bodies possess- 

 ing common characters, I propose that, to distinguish them 

 from crystals as above defined, they shall be termed "crys- 

 tallomorphs."^ Whether crystallomorphs are always modified 

 aggregate crystals (as in many cases they are) or sometimes 

 equivalent, as regards the order of crystal individuality, to a 

 simple crystal is not at all clear from published accounts on 

 the subject. If, then, we distinguish crystallomorphs from 

 crystals as just suggested, we are still justified in stating that 

 spicules are not crystals ; whether spicules are crystallomorphs 

 is a question I must discuss later. 



Three factors in the production of spicule forms are con- 

 ceivable: (a) The gross mechanical factor, or the shaping of 

 a structure due either to actual contact with surroundingf 

 objects (contact which, in this case, would affect the shape of 

 the spicule by influencing the scleroblasts depositing it and 

 not the spicule itself, which is a rigid structure) or to the 

 configuration of the secreting substance; {h) the influence at 

 a distance — actio in distans — of different parts of the organ- 

 ism on the scleroplasm ; and (c) the factor which produces 

 crystallomorphs. These three factors I will discuss as briefly 

 as possible. 



Factor (a) has been employed by several authors in the 

 interpretation of spicule forms with, however, but varying 

 success. The well-known line-of-least resistance theory of 



1 So far as I know, the iuflueuce of other crystalline substances in solution 

 on developing crystals is solely to give rise to very complex aggregate crystals 

 — not possessing curved surfaces (see Lehmann [12]). It is very probable, 

 however, that the presence of such crystalloid solutions greatly facilitates the 

 colloids in the production of complex crystallomorphs, probably being largely 

 instrumental in giving rise to variety of form. 



2 I originally proposed (British Association, York, 1906) the term " col- 

 loidomorph," but this is evidently defective. "Crystallomorph" is somewhat 

 awkward, but it seems to me preferable to Rainey's "coalescence body." 



