GENESIS. 293 



that has contracted the habit of annually migrating to the 

 sea, where it finds a food on which it thrives if the original 

 size of this species was not much greater than that of the 

 parr (which is nearly as large as some varieties of trout) 

 and if the limit of growth in the trout tribe is very indefinite, 

 as we know it to be; then we may reasonably infer that the 

 parr has nearly the adult form and size which this species 

 of trout had before it acquired its migratory habit ; and that 

 this production of milt is, in such case, a concomitant of the 

 incipient decline of growth naturally arising in the species 

 when living under the conditions of the ancestral species. 

 Should this be so, the immense subsequent growth of the 

 parr into the salmon, consequent on a suddenly-increased 

 facility in obtaining food, removes to a great distance the 

 limit at which assimilation is balanced by expenditure; and 

 has the effect, analogous to that produced in plants, of arrest- 

 ing the incipient reproductive process. A confirmation of this 

 view may be drawn from the fact that when the parr, after 

 its first migration to the sea, returns to fresh water, having 

 increased in a few months from a couple of ounces to five or 

 six pounds, it no longer shows any fitness for propagation : the 

 grilse, or immature salmon, does not produce milt or spawn. 



We conclude, then, that the products of a fertilized germ go 

 on accumulating by simple growth, so long as the forces 

 whence growth results are greatly in excess of the antagonist 

 forces; but that when diminution of the one set of forces 

 or increase of the other, causes a considerable decline in 

 this excess and an approach towards equilibrium, fertilized 

 germs are again produced. Whether the germ-product be 

 organized round one axis or round the many axes that arise 

 by agamogenesis, matters not. Whether, as in the higher 

 animals, this approach to equilibrium results from that dis- 

 proportionate increase' of expenditure entailed by increase of 

 size; or whether, as in most plants and many inferior 

 animals, it results from absolute or relative decline of nutri- 

 tion ; matters not. In any case the recurrence of gamogenesis 



