WAX SIMULACBA OF SHELLS. 231 



inclined to think that the surface of a block of paraffin-wax in 

 contact with a metal mould is cooled as quickly or even more so 

 than that in contact with water, at least in a cold room in January, 

 for the metal is a better conductor of heat than water, and is at a 

 low temperature to start with. If the form assumed by the block 

 was determined by the form of crystals the effect should be visible 

 on the free surface of either a block in a mould, or a mass on the 

 surface of water, for here the wax is free to take any form, 

 whereas elsewhere it takes the form of the surface in contact 

 with it. It is to be noted that Kappers gives no observations on 

 the form of crystals in paraffin-wax, and makes no attempt to 

 show that the form of his shell-like masses corresponded to the 

 form or aggregation of the crystals of which they were composed. 



With regard to the view that the forms in question are 

 dependent on rapidity of cooling, certain experiments which I 

 made with substances of a higher melting-point are important. 

 It is evident that the greater the difference of temperature 

 between the cooling medium and the melting-point of the molten 

 substance, the more rapid and sudden will be the solidifying of 

 the latter. Now I tried making the shell-like structures with 

 hard paraffin, that is with paraffin-wax of a high melting-point, 

 namely about 60° C, poured on to cold water, and the attempt 

 was a failure. The wax cooled so rapidly that the edge of the 

 cooled lower surface projected above the water and the molten 

 wax flowing on to the cooled portion was piled up on it and then 

 overflowed irregularly ; finally, as cooling proceeded further, after 

 the pouring w r as finished, the edges of the cooling mass curled 

 rapidly inwards owing to rapid contraction, and. the shape was 

 entirely spoiled. By pouring the same paraffin on to warmed 

 water, shell-like forms were produced, thus showing that rapid 

 cooling was not the essential condition. I also experimented 

 with bees'-wax, of which the melting-point is over 100° C, and 

 with this material nothing resembling the shell-like structures 

 could be obtained, simply because when poured on to water the 

 wax became at once solid all through and only irregular masses 

 were produced : the wax would not flow evenly over the solidified 

 layer in contact with the water, but formed a tangle of solidified 

 cords. 



The causes of the assumption by paraffin- wax of these shell-like 

 forms are, as I think I have shown, purely physical, and in itself 

 the subject may seem to be of slight importance and to have 

 little bearing upon zoology. But the subject acquires considerable 

 zoological importance from the fact that the phenomena have been 

 adduced in support of the view that the forms of molluscan shells 

 are determined by the form and behaviour of the crystals of 

 which their inorganic part is composed. For such a view the 

 phenomena discussed in this paper afford no support whatever, 

 and the doctrine itself has no scientific foundation. Considering 

 the diversity of molluscan shells in general, the different shapes 

 of Lamellibranch shells, the torsion of the Gastropod shell, and 

 the variety of the spirals shown among the Gastropoda, the third 



