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seems largely dependent upon the action of light. The more 

 exposed surface of spiral shells, and the posterior end of bur- 

 rowing bivalves, are usually more richly coloured or ornamented 

 than the less exposed or buried portions, and colouring generally 

 is probably of great biological importance. It is also, as in other 

 groups, most pronounced in brilliancy and variety in the warmer 

 regions of the globe, and becomes gradually reduced in diversity 

 and beauty as the poles are approached. These facts led Dr. 

 Fischer to propose for the Mollusca three zones of colouration 

 corresponding with the thermal ones. 



An examination of several thousand specimens of Helix 

 nemoralis from the sand-hills at Spurn Point, Yorkshire (one of 

 the driest spots in the kingdom), showed that scarcely a dozen of 

 them exhibited evenly developed and strongly marked banding ; 

 the bands, when present, were all more or less broken up and 

 disconnected. In this section of the general subject, Mr. Taylor 

 gives a score of excellent figures to illustrate his remarks. 



No less interesting are his observations on monstrosities. All 

 molluscs with spiral shells are liable to a reversal in the direction 

 of their convolution ; and bivalves, and even slugs, says Mr. 

 Taylor, are affected in an analogous way. The causes of this 

 reversal of the normal arrangement are, however, not at all known 

 or understood. M. Bourguignat has hazarded the suggestion 

 that it may be caused by electrical conditions, the electric current 

 flowing in the opposite direction to the embryonal rotation, the 

 essential conditions being a metalliferous soil, moist weather to 

 influence the latent electricity of the metallic substances, and the 

 conjunction of the atmospheric and terrestrial electricity, as by 

 thunder at the period of first manifestation of vitality by the 

 embryo. 



Prof. Carus, also, considers that the direction of the coiling of 

 the shell and animal may possibly be determined by the direction 

 of the embryonal rotation. These and other kindred topics are 

 fully discussed and elucidated by Mr. Taylor, who brings a wide 

 knowledge of the literature of the subject to bear upon his own 

 researches, and those of his colleagues. His remarks upon 

 Auxiliary and Protective Organs are especially interesting, but to 

 discuss them here is not possible in the limited space at our 

 disposal. We must be content to congratulate the author upon 

 the progress of his work, and recommend it to our readers as one 



