64 W. WOODLAND. 



of pliitei were supposed to be inherited for just tliis same 

 reason, viz. because ecliinoid larvae always had them ; never- 

 theless, as Herbst has shown, they are not inherited, since 

 they merely result from the elongation of the spicular rods. 

 It is indeed more than possible that the patterns on diatom 

 valves, radiolarian shells, and the rest are purely physical 

 products — ontogenetically determined — and that physicists 

 will some day be able to reproduce these patterns under 

 artificial conditions as Rainey did in the case of certain 

 organic calcareous structures. The perforations in diatom 

 valves and radiolarian shells it is true undoubtedly serve a 

 physiological necessity (since were thei'e no perforations, the 

 imprisoned organisms would die) and the organism is thus 

 evidently able to control to some extent the deposition of 

 silica, but physiological necessities ipso facto never yet pro- 

 duced ornamentations of no use or only incidentally of use to 

 the organism, and until the contrary is proved we are fully 

 justified in assuming for the reasons given and about to be 

 given that the forms of radiolarian and all other spicules are 

 not inherited.^ 



But there is a still more satisfactory answer with which to 

 reply to the criticism that radiolarian (and other) spicules^ 

 being, like cuticular products, cytoplasmic secretions, there- 

 fore owe their forms to the same cause, and this is that, as 

 all observers have agreed, spicules as a class do differ in 

 several very important respects from every other class of 

 cell-deposits. One of these differences is that, excepting 

 crystals, spicules are the only deposits assuming definite 



' Or only inherited in the sense that their form is determined by the 

 colloidal nature (see below) and architecture of the organism, which pro- 

 perties of course are inherited. Assuming that the forms of spicules are 

 "inherited " in this sense is very different to assuming either (a) tiiat every 

 individual scleroblast is guided by some unimaginable means to precisely that 

 position in the organism in which the spicule, which it is alone capable of 

 producing (by a power which no other class of cells is known to be capable of, 

 i. e. by forming an intracellular mould), is adapted to the economy of the 

 organism ; or (b) that every individual scleroblast is capable (in addition to 

 possessing the unique power just mentioned) of producing by heredity 



