K. E. von Baer's beginning insights into causal-analytical relationships during development

[摘要] AnumberofcommentsscatteredthroughoutthetextofvonBaer'sUeberEntwickelungsgeschichtederThieresuggestthatvonBaerhadconsiderableinsightintothedynamicsofepigenesis,andthathewasawareofcausalrelationshipsindevelopment.Inpostulatingthemannerinwhichdevelopmentproceedsfromthegeneraltothespecial,heconsideredthattherearethreekindsofdifferentiation:differentiationintogermlayers,andhistologicalandmorphologicalsegregation.Heemphasizedthedichotomousnatureofhistologicalsegregation,statingthatitevokescontrasts,andforoneexamplestatedthat,whenanerveisformed,therewasnotnothingtherebeforebutacommonmassthatseparatesitselfintonerveandnot-nerve.Hespeaksofhistologicalsegregationasplastic,andthereisevidencethatheenvisageddifferentiatingtissuesasmodifiableintheirdevelopment.Hestatedspecificallythat“eachstepindevelopmentismadepossiblebytheimmediatelyprecedingstateoftheembryo.”Hestated,foranexample,that“theeyeseemstobeanoutgrowthofthenervetubethatprotrudesthroughthemusclelayerasfarastheskinlayer,andtheouterpartsoftheeyearechangesintheskinevokedasaresult.”Bytheouterpartsoftheeyeheprobablymeanttheeyelidsandnictitatingmembrane,butitisinterestingthathebelievedtheopticrudimenttoevoketheformationofotherstructuresbytheskin.VonBaeralsoattemptedtoexplainselectedembryologicalphenomenainphysicalterms(electromagnetism,galvanism)andbelievedthatsomeofthemmightbeopentoexactphysicalinvestigation.Itmaywellbethatsuchpassagesexertedaninfluenceonthedevelopmentoftheideasoflaternineteenthandearlytwentiethcenturyinvestigatorswho,inGermanyatleast,mustcertainlyhavereadthem,andtheymaythushaveplayedtheirpartinleadingtowardourmoderndynamicconceptsofepigenesis.

[学科分类] 生物科学（综合）