experiments, made with a view of ai<certaiiiing the ago of 

 animals and especially of his study of the habits of the com- 

 mon marine snail, (Natica Heros), found upon our beaches. 

 He desired to ascertain, if he could, its rate of growth, and for 

 that purpose had gathered about a thousand specimens 

 of various sizes, within a few days. These he had assorted, 

 and found to bo easily divided iiito groups, each group being 

 of a certain definite size, and there being none of interme- 

 diate growth. He had previously ascertained that snails 

 always spawned at the^same time, once a year, and that the 

 process continued but a few. days. He therefore knew that, 

 each of his groups of snails—those of the same size — were 

 'of the same age, having commenced growing at the same 

 time ; and having grown under precisely the same circum- 

 stances, were therefore so mucli alike. He thus ascertained 

 the various ages of the Naticas found together upon one 

 beach from those of one or two years up to those of twenty- 

 five or thirty years — the latter being the age of the largest 

 snails usually found upon the beach. He also noticed rings 

 or transverse lines upon the snail shells, more distinctly 

 marked than the ordinary lines of growth, the number 

 of which indicated very nearly their age ; for these 

 lines coincided with tlie ordinal number of the different 

 set of specimens arranged according to their size. He 

 had thus, he thought, ascertained the rate of growth of 

 these shells. A comparison with other families however, 

 shows a widely different result. Among the larger land- 

 snails, (Helices), some species may reach in one year the 

 dimensions which a Natica takes from ten to fifteen years 

 to attain. Again, some of our Unios, such as U. cylin- 

 dricus, require at least fifteen years to acquire their full 

 size, while our Pinnas reach to their full dimensions in seven 

 or eight years. It is by a similar process, he said, that we 



