NOTICES OF BOOKS. • 335 



accepted — and this applies with equal force to the Radiolaria 

 referred to above — we shall be led to understand two striking 

 features of these groups of Protozoa ; on the one hand, the very 

 large number of diverse types or families and the large number 

 of species and varieties within each, and on the other hand, the 

 persistence of forms from very early periods to the present time. 

 " In the order of physical and mathematical complexity there 

 is no question of the sequence of historic time. The forces that 

 bring about the sphere, the cylinder or the ellipsoid are the 

 same yesterday and to-morrow. A snow-crystal is the same 

 to-day as when the first snows fell. The physical forces which 

 mould the forms of Orbulina, of Astrorhiza, of Lagena or of 

 Nodosaria to-day were still the same, and for ought we have 

 reason to believe the physical conditions under which they 

 worked were not appreciably different, in that yesterday which 

 we call the Cretaceous epoch ; or, for ought we know, throughout 

 all that duration of time which is marked, but not measured, 

 by the geological record." 



The shapes of horns, of leaf-arrangement and phyllotaxis 

 and the shapes of eggs are dealt with, and the book closes with 

 a fine discussion, which is by no means the least interesting and 

 important, on the Theory of Transformations or the Comparison 

 of related forms. The comparison is made by means of Cartesian 

 co-ordinates within which are inscribed the outlines of related 

 organisms or their skulls. 



In taking leave of this interesting and suggestive book, sug- 

 gestive alike to the biologist and mathematician, we offer our 

 congratulations to the author and to the syndics of the University 

 Press on its production. 



