142 ANATOMY AND LIFE HISTORY OF MOLLUSCA. 



To return now to the shell of which an enlarged figure is given 

 at pi. 1, fig. 1, magnified about eight or ten diameters. In this 

 plate it should be remarked the full ornamentation of the shell is 

 not given, but only a sketch of the general design and detail of 

 two ribs. It is supposed also that the shell has all its 

 ornamentation in full detail, which I may state is a thing that is 

 seldom or never met in nature. The smaller ribs are always 

 more or less irregular, and sometimes the larger ones are, so to 

 speak, aborted, as if it were undecided whether they were 

 intended to be large or small. The nodules on the smaller ribs 

 are often raised, scale-like imbrications, but this as well as the 

 colouring is inconstant. The plate represents an ideal shell of a 

 species which, like every other in nature, is subject to great 

 variations. The apex is anterior, and from it proceed in a 

 radiate manner about 40 or sometimes as many as 50 conical 

 ribs ; sometimes, but not always, large and small alternated. 

 These ribs are interrupted at intervals with somewhat 

 inconspicuous lines of growth. The whole shell is clouded and 

 stained with lines and blotches of colour as already mentioned. 

 These lines are not confined to the ribs or to the depressions 

 between them ; though sometimes they very conspicuously form 

 double lines at intervals on the smaller intercalated ribs at each 

 side of most larger ribs. There is generally a line of colour on the 

 testaceous fold of the mantle corresponding with the lines of 

 colour on the shell. I have already referred to the possible 

 connection between pigment-coats and these testaceous markings. 

 There is a very thin chitinous periostraca on all the shells, which 

 serves effectually to conceal the minor details of the shell-surface. 

 If, however, it is moistened with spirit or clove oil, a wonderful 

 sight will be presented to a good and powerful hand-lens. A 

 number of minute points shining with intense brilliancy are 

 scattered irregularly and somewhat numerously over the whole 

 shell-surface. No particular symmetry can be detected as yet, and 

 even it may require some little experience to perceive them at all. 



The sight presented is a very marvellous one, and forcibly 

 recals the brilliant points of light sparkling out of the darkness 

 in the field of a telescope directed to the heavens at night. One 

 realizes the truth of the saying that what the telescope is to the 

 astronomer, the microscope is to the naturalist. Possibly there 

 is not so much awe and mystery connected with these little 

 diamonds so brilliantly reflecting into the tube of the microscope, 

 for we know that with the aid of this instrument we can resolve 

 the whole structure of even the most minute in a manner we 

 are yet far from being able to do with the stars. 



In order to see the full extent and beauty of the arrangement 

 of the eyes on the shell, a little manipulation is necessary. It 



