63 



lingen at finde iioget stucliuni, der i bygning eller dannel- 

 sesina:ide icinule sammenlignes med det enibryonale gastrnla- 

 stadiuni. Ved lueraiere betragtning viste det sig. at det 

 toliladede knopanheg, der fremviste en vis ydre liglied med 

 en gastrula. dog var en væsentlig anderlcdes bygget form- 

 dannelse. 



Jeg vil med faa ord soge at redegjore for. hvorledes 

 disse forhold kan opfattes i theoretisk henseende. Forst 

 og fremst vil jeg fremhæve, at mine loulersøfjeber ikke til- 

 lader nogen slutning angnaende det siiorgsniaai. iivorvidt 

 Ascidieiidviklingen overhovedet er en rekapitnlation. 

 Dette er et si)Orgsmaal. der gaar langt ud over underso- 

 gelsernes ramme. Vort maal er deriniod at levere et bi- 

 drag til lovene for de formstadiers dannelse, der almindnlig 

 bekrives som rekapitulationsstadier. 



Hvis min fremstilling af A scidiernes udvikling er rig- 

 tig. saa fremgaar deraf. at det. der almindelig Ijeskrives 

 som rekapitnlation af den fylogenetiske udvikling. er en 

 orerordeutlirj variabel falior i iiidividernef^ advi/dinc/sJiisforie, 

 hvis opfrædeii si/nes lieJf ajliængig af. om den er af hefyd- 

 mng for itdviJdinr/sf^tadierne selv. Vi har seet, at en Asei- 

 die i knoinulviklingen kan dannes uden i sin ndvikling at 

 gjennemlolie noget gastrula- eller larvestadium. 



Er det nu berettiget som ovenfor af knopudviklingen 

 at drage almindelige slutninger over udviklingens principer? 

 Tidligere forfattere har ment. at knopudviklingen i det hele 

 er en proces, der i sit væsen nærmest er at opfatte som 

 en delingsproces. hvor ingen nydannelse forekommer. Efter 

 de specielle resultater, som er fremlagt i dette arbeide, er 

 dog ikke længer en saadan opfatning mulig for Ascidiernes 

 vedkommende. Yi saa knoppen begyude som et ganske 

 lidet, særdelas primitivt anla'g, og organndviklingen viste 

 sig i sit forløl) ikke væsentlig mindre compliceret end i 

 den enibryonale udvikling. Da nu de dyr. der dannes ved 

 knopudviklingen i alle liensender er identiske med de dyr, 

 der fremgaar af larverne, saa maa den ene dannelsesmaade 

 ligesaafuldt som den anden i sit væsen kaldes en nydan- 

 nelse, en ndvikling. Diiescli siger træflende angaaende de 

 forskjellige forsøg. der er gjort paa at opfatte al knopskyd- 

 ning som regeneration, deling (16, pag. 121): ,,Schliesslich 

 kann man ja aber auch die Entwieklung aus dem Ei Re- 

 generation nennen : es fehlt eVien alles liis anf eine Zelle; 

 eine solciie ^^'ortverwendung wiirde uns freilich nich: weiter 

 bringen.-' 



Om knopudviklingen end ikke helt kan sammenlignes 

 med embryonaludviklingen, saa er den dog iallefald en saa 

 distinct udviklingsproces, at ogsaa den maa kunne belære 

 os om udviklingens væsen overhovedet. 



Det paafaldende er imidlertid da, at det hele skema 

 for organndviklingen hos knopperne er saa overordentlig 

 forskjellig fra organdannelsen hos ægget, medens erfaringen 

 ellers viser, at selv fjerntstaaende gruppers embryonalud- 

 viklinger indbvrdes stemmer meset overens. Saaledes staar 



development, any stage which. in structure or manner of 

 formation could be compared with the endiryonic gastrula 

 stage. On more careful consideration, it proved that t!ie 

 two-layered l)ud-rudiment. which had a certain external 

 resemblance to a gastrula, was yet a formation of an essen- 

 tially different structure. 



I will l)rietly try to show iiow tliese facts may !k' 

 regarded from a theoretical ])oint ol view. I v.-ill tirst of 

 all lay stress upon the fact tliat my iiive.itiyations do not 

 permit of any conclusion lieing drawn on the ipiestion as 

 to how far Ascidian development, on the whole. is a re- 

 capitulation. Tliis is a question wiiicii goes far beyond 

 the scope of our investigations. Our object, on the otiier 

 hand, is to make a contriltution to the laws for the forma- 

 tion of thoso form-stages whicli are generally described as 

 recapitulation stages. 



If my account of the development of Ascidians is 

 correct, it follows tliat what is generally described as a 

 recapitulation of tlie pliylogenetic development, is an e.r- 

 ceediiiyly rariahle facfor in fJie developmenfal Iiislory of ihe 

 animal and one irliose appearanee seems to depend eiifirehj 

 tipon iis sigiiifcatioji fo ilie developniental stages themselves. 

 We have seen that in bud-development, an Ascidian can 

 be formed without going through any gastrula or larva 

 stage in its development. 



Are ^ve justified in drawing from the bnd-developnient 

 general conclusions, as aljove, as to the i)rinciples of deve- 

 lopment? Earlier -writers have thought that bud-development 

 on the whole is a process which. in its nature, should 

 more propeidy l)e regarded as a tission process. where no 

 new formation oceurs. According, how-ever, to the s])ecial 

 results set forth in this paper, such a view is no longer 

 tenable, as far as Ascidians are concerned. We saw the 

 bud begin as a very small, exceedingly primitive rudiment; 

 and the development of the organs proved to be in reality 

 no less complicated in its course, than in that of the em- 

 bryonic development. As the animals formed l)y Imd-de- 

 velopment are identical in every respect with those pro- 

 ceeding from larvæ, the one mode of formation must be 

 considered in its nature to be tpiite as much a new forma- 

 tion, a development, as the other. Driesch very aptly says 

 concerning the various attempts that liave been made 'to 

 rcgard all budding as regeneration or fission (16, p. 121): 

 ,,Schliesslicli kann man ja aber auch die Entwicklung aus 

 dem Ei Regeneration nennen: es fehlt eben alles bis auf 

 eine Zelle ; eine solche Wortverwendung wiirde uns freilich 

 nicht weiter bringen." 



Although bud-development does not altogether admit 

 of comparison with embryonic development, it is at any 

 rate so distinct a developmenfal process as to be capable 

 of teaching us about tiie nature of tlie development in 

 particular. 



The remarkable thing however is tiutt the whole 

 schema of organic development in the Inids is so exceed- 

 ingly different from the organ -form at i on in the ovum, while 

 experience elsewhere siiows that even in widely separated 

 groups, there is a great mutual agreeraent in the embryonic 



