232 THE INPUCTIONS OF BIOLOGY. 



in such case, n. concomitant of the incipient decline of 

 growth naturally arising in the species, when living under 

 the conditions of its remote ancestors. If this be admitted, 

 the immense subsequent growth of the parr into the salmon, 

 must be regarded as due to a suddenly -increased facility in 

 obtaining food — a facility which removes to a great distance 

 the limit at which assimilation is balanced by expenditure ; 

 and which has the effect, analogous to that produced in 

 plants, of arresting the incipient reproductive process, and 

 causing a resumption of growth. 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. But without citing further illustrations, or 



attempting to meet further difficulties, it has, I think, been 

 made sufSciently clear, that some such connexion as that al- 

 leged, exists. Traversed, as is this relation between commence- 

 ment of sexual reproduction and declining rate of growth, by 

 various other relations, it is quite as manifest as we can 

 expect it to be. 



The general law to which both homogenesis and hetero- 

 genesis conform, thus appears to be, that the products of u 

 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 

 Qxes that arise by agamogenesis — whether the development 

 be continuous ir discontinuous ; matters not. Whether, as 

 in concrete organisms like the higher animals, this approach 

 to equilibrium results from that disproportionate increase of 

 expenditure entailed by increase of size ; or whether, as ia 



