12 The American Naturalist. [j n 



preceding maturity, as compared with the preceding genera- 

 tion, and retardation signifies a reduction of the numbers of 

 such repetitions during the same time." Thus, from Cope's 

 point of view, tachygenesis is the law of progression, and re- 

 tardation is the law of retrogression, and they are both essen- 

 tial parts of his law of acceleration and retardation. 



Haeckel alludes in general terms to the law of abbreviated 

 development in his " Morphologie der organismen," and in his 

 "Anthropogenie," published in 1874, substantially agrees with 

 Cope in his view of the law and uses the term " palingenesis " 

 for the exact repetition of characteristics which occurs in the ear- 

 lier and simpler forms of a phylum and " coenogenesis " for the 

 abbreviated or highly accelerated cases of inexact parellism of 

 the young of more complex forms with their ancestors. There 

 is, however, an objection to this mode of using the last term 

 which I mentioned also in writing the paper quoted. 3 



3 During the writing of this paper I took from Cope the statement made above, 

 although unable to find any verification of it in HaeckePs Anthropogenie (Island 

 2d editions both dated 1874), but, since the above was in press, I obtained a copy 

 of the 4th edition (1891) and the reading of this has caused me to entirely alter 

 my opinion with regard to HaeckePs opinions. He certainly had at that time, 

 1 391, what seems to me erroneous and inadequate view of the nature and action 

 of the laws of tachygenesis and <ras>- ir 



Haeckel states (Anthropogenie, 4th edition, Leipzig, p. 9, 1891) that ''Palin 

 genetische Processe oder keimesgeschichtliche Wiederholnngen nennen wir alle 

 jene Erscheinungen in der individuellen Entwickelungsgeschichte, welche durch 

 die conservative Vererbung getreu von Generation zu Generation ubertragen 

 worden sind und welche demnach einen unmittelbaredEuckschluss auf entsprec- 

 hende Vorgange in der stammesgeschichte der entwickelten Vorfahren gestatten- 

 Cenogenetische Processe hingegen oder ' § , n ,igen nennen 



l der keimesgeschiehte, whelche nicht auf solche verer- 



• Jugendyorm an bestimme Bedingungen der Keimesent- 

 *i sind. Diese ontogenetischen Erscheinungen sind 



dnrrJmus knnnr uumittdhnn-n ScMhxx auf vntapr,><'hemle 

 mrsf/whi.cht>> der Ahnenreihe erlauben, vielmehr die Er- 

 - lien und verdecken." 



lews shortened or abbreviated development in a very dis- 

 to which I am accustomed. He speaks of it as due to iK* 

 •oduction of " fremdezuthaten " as " Cenogenetische oder Stor 



