ANATOMY AND LIFE HISTORY OF MOLLUSCA. 133 



the rule rather than the exception amongst the Mollusca. It is 

 now many years since I first noticed the peculiar ornamentation 

 with which some of our coast shells are varied ; more particularly 

 in the radiating lines and papilke or warts, with which the surface 

 is adorned. This is more conspicuous amongst the bivalves, and 

 I was often struck, when examining them with a lens, at observing 

 the peculiar crystalline clearness of some of these asperities upon 

 their summits. In Anatina tasmanica, Reeve, to which further 

 reference will be made, this is especially conspicuous. The whole 

 exterior surface of the shell is rough with little dots, not 

 symmetrically placed, nor uniform in size, though small and 

 sometimes aggregated together in little clusters. But what struck 

 me most about these little marks was, that when I examined them 

 with a lens, I found that each had a little transparent crystalline 

 summit which brightly reflected the light. But almost any shell 

 in its natural state, if carefully examined, I had noticed, had 

 something of the same kind upon its surface. [Jsually this was 

 so small, that a rather powerful hand-lens was required for its 

 detection. Keeping to the example that I have used all through 

 this paper, I may mention the limpets. In a good shell that had 

 not been much eroded, my attention was early called to certain 

 little marks and dots upon the upper surface which must, I felt 

 convinced have had some meaning. As a rule they appear 

 like little stained pits and depressions, but sometimes forming 

 raised clusters of crystalline projections which correspond with the 

 ornaments on the shell. It never occurred to me to suggest that 

 they were eyes, but I felt convinced they had a purpose, and that 

 an important one, in the economy of the shell. I was equally 

 interested with the glassy hemispherical projections on the 

 calcareous opercula ot many shells, especially Nerita and the 

 trochiform and turbinate Gastropods. The latter still remain a 

 partially unsolved problem to me. One circumstance that served 

 me as a clue, was in the case of Lima multicostata, Sowerby, a 

 bivalve, the hooded imbrications on which make a beautifully 

 ornamented shell, covered with sharp asperities. Each of the 

 little hooded scales I observed, had one or a cluster of the small 

 crystalline nodules within it, often at the summit, and I could not 

 help remarking years ago, that it looked to me like a bull's-eye 

 lens placed in a reflector, in a most advantageous position to give 

 light to the animal. Furthermore, even the smooth univalve shells 

 were observed to have a very minute ornamentation of this kind 

 in the fine strise which follow the spiral windings of the whorls ; 

 but I did not pursue the subject further, though convinced that 

 such a uniform ornament must have a meaning. Structures with 

 no higher purpose than mere ornament are unknown in nature, 

 and perhaps the tendencies of the doctrines of evolution incline us 



