1864.] SENATE— No. 22. 11 



continue stationary afterwards for an indefinite period of time. 

 But this is not the case with a very large number of them, the 

 growth of which is slow and long continued, and I have suc- 

 ceeded in devising a very simple method of ascertaining their 

 age at once, provided it be known that they breed at a fixed 

 period in the year. This being known, all that is necessary to 

 determine the age of any individual of the species, is to gather 

 a very large number of specimens of every size, from the smallest 

 to the largest, and to arrange them in sets, according to their 

 size. As all were born at the same season, the difference of 

 size between the smallest and those of the next set is of course 

 one year, and so on for every set. So the ordinal number of 

 every set gives the age of all the specimens belonging to it. 

 The large collections of specimens of our common species of 

 marine animals, amounting frequently to many thousand speci- 

 mens of the same species, have been gathered for this purpose. 

 I have thus ascertained that the medium size of an adult Natica 

 Heros is reached in about thirty years ; that of most of our 

 Unio and Anodontas reach their full size in from twelve to fifteen 

 years ; that our common Pinna is full grown in six or seven 

 years, &c. Once upon this track, it will be easy to ascertain 

 the rate of growth of most animals. I may already mention 

 that specimens of our common Starfish of ordinary size are at 

 least ten or eleven years old ; while our largest Jellyfish, 

 measuring over six feet in diameter, attain their full size in a 

 few months. 



These collections of numerous specimens of the same species 

 have led to another unexpected result, which may be expressed 

 in these words : The differences noticed among animals of the 

 same species do not constitute varieties, but are individual 

 differences, similar to those which may be noticed among the 

 different individuals of the same family among ourselves. Any 

 attempt to group them under a few heads as varieties fails, as 

 soon as large numbers of specimens are considered. What 

 have been generally described as varieties by naturalists are 

 extreme individual differences occurring more frequently in 

 certain species than in others, but like all others presenting 

 the same indefinite peculiarities which forbid considering them 

 as in any way typical. This shows that individuality consti- 



