SVEN OTTO HÖRSTADIUS 18February1898—16June1996 ElectedFor.Mem.R.S.1952 B C.-O.J Departmentof AnimalDevelopmentandGenetics,UppsalaUniversity, Uppsala,Sweden I During the past few decades, developmental biology has become one of the most exciting areas of science. This is largely a result of the rapidly growing knowledge of molecular biology, partly resulting from the achievements of earlier generations of embryologists. One of themenof specialimportanceamongtheembryologistsof thetwentiethcenturywasSven Hörstadius.Mostof thecontentintoday’sbiologytextbooksdescribesresultsfromthepost- Watson–Crick era. However, few texts exclude figures and facts from Sven Hörstadius’s dissertationof exactlyseventyyearsago.Hisexperimentsonseaurchinlarvaeshedlightona couple of the most central findings in developmental biology, namely that the uneven distributionof theegg-cellcontentsgivesrisetoearlyembryocellswithshiftingqualities,and thatcommunicationbetweenthesecellshasanessentialroleinthedifferentiationprocess.In the same way, his achievements on the neural crest and its impact on head development in vertebrateshavebeenof lastingimportance.
246 Biographical Memoirs E Sven Hörstadius was born on 18 February 1898. He passed away in 1996, and well into his nineties he was both physically and mentally in good shape. He was raised in Stockholm, wherehisfather,WilhelmHörstadius,wasahigh-rankingjurist(Judgeof Appeal)andSven’s childhoodcontainedthenormalingredientsof anupper-classStockholmenvironment,which meant for instance a good education, outdoor life and summers in the archipelago outside Stockholm.
248 Biographical Memoirs partsof theechinodermembryo.InthosedaysKristinebergwasalessdesirableplacetowork atduringthecoldpartof theyear,especiallyforaresearcheronseaurchins.Thetwospecies availablethere,Echinusesculentusand Psamechinusmiliaris,donotspawnduringthisperiod of theyear.TheNaplesstationwastobehisfavouritewinterlaboratory,eventhoughhequite oftenalsovisitedRoscoff inFrance,Plymouthandotherstations.Duringhisveryfirstvisits to Naples in 1922 and 1924 he began his career in echinoderm biology by making his first experiments on the isolation of larval fragments to reveal the process of determination, i.e.
250 Biographical Memoirs embryos. They migrate quite early into the interior of the heap of cells and later form the skeleton. Earlier observations of this phenomenon were confirmed by Hörstadius after he had performed batteries of elegant experiments. Through several types of vital-staining experiment he also was able to settle the old subject of contention of where the boundary betweenthefutureectodermandendodermissituatedinearlystages.
Sven Otto Hörstadius 251 embryogenesis to the development of head organization. There could be more than one explanationforthisswitch.Foramanwhowasraisingafamily,seaurchinstudieswerereally favourable for a Swede during the summer months, when the Kristineberg station was the ideal place for children on school holiday. However, long winter and spring stays in Naples were difficult to cope with, both for an academic and for a family man. However, another factor might have been even more important: he naturally wished to acquire an academic chair, and in those days Swedish universities seldom gave a professor’s position to a scientist who did not have a very broad scientific experience. If his skill in invertebrate cell biology together with his early bird ecology papers could be supplemented with vertebrate morphologyandembryology,hewouldbebetterequippedforachairinzoology.
252 Biographical Memoirs (a) (b) (c) (d) Figure2.Thisfigureshowshowvital-stainedectomesenchymematerial(a)migratesundertheepidermisto takeuppositionas,forexample,presumptivegillarches(candd).(FromHörstadius&Sellman(1946).) his lectures Hörstadius told the whole story of how our knowledge of these important cells had been built up, all the way from Wilhelm His’s first description (His 1868) of the neural crest in the chick embryo, where it was reported that the cranial ganglia emanate from these cells. However, Hörstadius not only gave a report of the different findings: he also made a criticalanalysisof eightyyearsof experimentation.