HYATT. — ORGANIC CYCLES. 223 



Ou the other liuiul, after tlic acme is passed and the paracme sets in, 

 there is a sensible quickening of evolution during decline. 



Phylogerontic forms become more and more numerous, and there are 

 wider departures in the structures from the acmatic forms than any of the 

 divergences that occur within the acmatic forms themselves. 



The hopping, skipping, and at last the jumping, begins in the extremes 

 of the series, so that it becomes difficult, as has been shown by the author 

 in a number of series, and by Cope when giving illustrations of the action 

 of the law of tachygenesis, to connect one of these extreme forms with 

 its nearest conireners. 



The characters of the cycle in the ontogeny are here again similar to 

 those of the phylogeny ; thus the final substages of the gerontic stage are 

 wider departures from the ephebic substages than these are among them- 

 selves and when compared with each other. The analogy of the old with 

 the young shows this most conclusively, and the similarity of phylogeron- 

 tic and pliylonepionic forms in the same stock occurs in the phylogeny. 



In fact, there is no end to the homolocjical and analosfical similarities 

 and parallelisms of ontogeny and phylogeny wherever both are found 

 complete. 



There are types in which the ontogeny is incomplete, as among insects 

 and other jjurely seasonal animals, and in these it becomes difficult, if not 

 impracticable, to study the gerontic stages, and thus translate the phylo- 

 gerontic types if they occur. These same types, and others also, present 

 difficulties in their larval stages, owing to their indirect modes of develop- 

 ment, which have been discussed by the author in -'lusecta" and other 

 publications, and need only be referred to here. 



One of the bearings of these researches is of interest on account of the 

 discussions between biologists, geologists, and mathematicians with regard 

 to the length of time that life has existed on this planet, and the bearing 

 of this upon calculations with regard to the age of the earth. It cannot 

 be assumed that the time ratio was the same during the Eozoic or Pre- 

 Paleozoic as during the Paleozoic or the Mesozoic, so far as the evolution 

 of forms is concerned. 



The author in other publications has claimed that this must have been 

 the law, and explained the phenomena as parallel with that which takes 

 place at the beginning of every series arising in the Paleozoic and 

 Mesozoic, and also according to Minot's law of growth and other phe- 

 nomena of the earlier stages in the ontogeny of every animal. 



The evidence is very strong that great structural differences were 

 evolved much more quickly in these early times, and the probabilities 



