ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 473 



in a ling (Molva molva). Finally, the author describes a plaice without 

 the left eye. There is not much evidence of a traumatic lesion. On 

 the other hand, the absence could hardly be congenital, since the eye- 

 muscles are almost normal and the optic nerve is considerably developed. 

 It is suggested that a failure to form the lens in early development may 

 have led to the abnormality. The bulbus oculi may have degenerated, 

 while the optic nerve, having its trophic centre in the brain, persisted. 



INVEETEBEATA. 



Mollusca. 

 a - Cephalopoda. 



Simulacra of Molluscan Shells.*— J. T. Cunningham discusses 

 the simulacra of shells which Kappers produced in paraffin-wax. Kappers 

 adopted the conclusion of Harting and Bedermann that the form and 

 characters of Molluscan shells, as well as those of otoliths, egg-shells, 

 and the skeletons of Foraminifera, Alcyonaria, and Echinoderma, are 

 due to the aggregation of crystals of calcium salts formed within a 

 colloid medium, the crystals being of a special kind called sphsero- 

 crystals or calcosphrerites. Kappers maintained that paraffin-wax shares 

 with calcium salts the property of forming sphaerocrystals, and that the 

 formation of crystals from a solution takes place in essentially the same 

 way as in the solidification of a molten mass. 



According to Cunningham the form and markings of the simulacra 

 are not to be explained by any effect of crystallization, but were due, 

 as in the case of Molluscan shells, to the successive addition of accretions 

 in a particular direction. He poured molten paraffin-wax into water and 

 obtained all sorts of simulacra. 



Large prismatic crystals are formed when the cooling is slow, and 

 they assume a stellate arrangement where there is most freedom of 

 movement, i.e. near or at the free surface, as on a glass slide, or at the 

 surface of a block, or floating shell-like mass. When the cooling was 

 rapid, as at the surface in contact with water or in contact with the 

 metal of a mould, neither large crystals nor stellate arrangement occurred ; 

 the structure is more compact, apparently because the wax becomes 

 solid at numerous closely crowded points at the same time, and crystals 

 if formed at all are verv minute. In no case did Cunningham observe 

 crystals having any approximation to a spherical form. The form and 

 markings of Molluscan shells are not determined by the form and 

 behaviour of the crystals of which their inorganic part is composed, but 

 by the conditions of the mantle. The only resemblances between the 

 real shells and their wax counterparts, is that they are both formed 

 by successive accretions to the edge ; the marks of the boundaries of 

 these accretions are due, in the case of the wax, to interruptions of the 

 flow by cooling of the lower layer and surface tension, in the case of 

 the real shell, to " waves " of growth of the causes of which we are 

 quite ignorant. 



* Proc. Zool. Soc, 1915, pp. 225-34 (5 figs.). 



