11 



En fornyet uudersøgelse tik spørgsmaalet af van Bene- 

 deii Of/ Julia (o). Peribranchialsækkens dannelse skildres 

 af dem saaledos, at det ydre blad oi)staar af ektodermen, 

 (let indre af entodermen.*) De indtager doij et væsentligt 

 andet standpunkt angaaende peribranchialsækkens morpho- 

 logiske betydning end Ddla Valle. Angaaende sannnenlig- 

 ningen mellem coelomet hos Echinodernier, Sagitta, Aniphi- 

 oxiis og peribranchialsækken hos xlscidiernc siger de: ,,L'on 

 ne pent done comparer a ces formations les saccules latér- 

 aux (jui aparaissent beaucoup ])lus tard dans la partie 

 anterieure de la larve de la Clavelline aux cotés du sac 

 branchial: ils ne contribuent en rien å la formation des 

 tissus conjonctifs, des nuiscles et des elements figurés du 

 sang; mais ils intervieunent dans la formation de Tépithé- 

 lium peril>ranchial concurremment aver Tépiblaste." 



Seellr/er bavde imidlertid allerede tidligere (58) liekra^f- 

 tet Kol val ei' sky f: undersogelser og fundet. at peribranchial- 

 sækken helt var af ektodermal oprindelse. Klart fremgaar 

 dette af følgende beskrivelse (58 pag. 83): ,.Die Bliischen", 

 der dnnnes ved indbugtning af epidermis, „breiten sich 

 nun zwischeu Hautschicht und den seitlichen Wandungen 

 des Kiemendarmes betrik-htlieh aus. um denselben schliess- 

 lich Ins zum Endostyl venti'al\varts hin zu unnvachsen". 

 ..Wilhren die beiden Peribranchalblaschen sich ausbreiten. 

 treten sie mit iiiren inneren Wiinden zu dem Kiemendarra 

 in innigste Beziehung. Es kommt namlich zur Bildung 

 der Kiemenspalten-'. Af senere arbeider nævner jeg her 

 fremforalt Willey, der bekræitede Kourilcvski/s og Seeligers 

 fremstilling, idet han samtidig indgaaende studerede g^jælle- 

 spalternes dannelse (^et sporgsmaal, som jeg her kun leilig- 

 hedsvis vil berore). Willey undersogte Cionu infextinalis 

 og Clarelina Icpiidiforuiis. Pag. 338 (66) siger han: ,.From 

 observations made on Ciona intestinalis and Clavelina lepadi- 

 formis I can contirni Kowalekslqj and Seeliger in saying 

 that the atrial cavities of Ascidians are derived essentially 

 from ectodermic invaginations; and that tho idea that the 

 visceral wall of the atrium is derived from the hypoblast, 

 as put forward by ixin Beiieden aud Julin, is entirely 

 without founchxtion." Som nævnt i mit arbeide (31) pag. 

 592 har jeg havt anledning til at studere Wdlei/s jn^æpara- 

 ter, og der var elter min mening ingen tvivl om disses 

 afgjørende betydning ior sporgsmaalet. At de vanskelige 

 forhold under undersogelsen let kan misforstaaes, var mig 

 imidlertid indlysende. Betragter man W/Ueys fig. 28 Pl. 

 XXXI (66) at, vil man indsc, hvor let et saadant billede 



*) Xaar Herr SeclUjey luir fundet det at være af vigtighcd at kon- 

 statere, at jeg i en ioreløbig meddelelse har fremstillet van 

 Beneden og Julin som forfægtere af peribranchialsækkens dan- 

 nelse fra ektodermen, vil en læsning af mit udførlige arbeide 

 kunne overbevise ham om, at dette ikke har beroet paa uogen 

 „Irrthum". Da Botryllusknoppens indre blære dannes af peri- 

 branchialsækkens parietale blad. er ogsaa efter van Beneden og 

 .Julins undersogelser Botryllusknoppen en ektodermal dannelse. 

 At konstatere dette var mit eneste maal med en diskussion af 

 litteraturen over perilminchialsækken. 



The subject imderwent renewed investigatiou by van 

 Beneden and Julin (3). In their account of the formation 

 of tlie peribranchial cavity they state that the outer laver 

 originates in the ectoderni. the inner in the endoderm.*) 

 They take up an essentially different stand-point, however. 

 from Della Valle, with regard to the mtn-phological signiti- 

 cance of the peribranchial cavity. Witli ret:ard to the 

 comparison between the c(eloma in Echinoderms, Sagitta 

 and Amphioxus, aud the poribranehial cavity in Ascidians, 

 they say: ,.L'on ne peut done comparer a ces formations 

 les saccules latéraux qui apparaissent beaucoup phis tard 

 dans la partie anterieure de la larve de la Clavelline aux 

 cotés du sac branchial: ils ne contribuent en rien ii Li 

 formation des tissus conjonctifs. des muscles, et des elements 

 figurés du sang; mais ils intervieunent dans la formation 

 de répithéliuni péribrancliial concurremment avec Tépi- 

 blaste." 



Seeliger, however, had already (58) contirmed Koiva- 

 levskys investigations, and found that the peribranchial 

 cavity was entirely of ectodermal origin. This is clearly 

 shown in the following description (58, p. 83): ..Die Bliis- 

 chen"', whicli are formed by an invagination of the epider- 

 uiis, ,,breiten sich nun zwischen Hautschicht und den seit- 

 lichen Wandungen des Kiemendarmes betrjichtlich aus. um 

 denselben schliesslicli bis zum Endostyl ventrahviirts hin 

 zu umwachsen". .. Wiihrend die beiden Peribranchialblii- 

 schen sich ausbreiten, treten sie mit ihren inneren Wiinden 

 zu dem Kiemendarm in innigste Beziehung. Es kommt 

 niimlich zur Bildung der Kiemenspalten.-' Among more 

 recent writers, I would first of all name Willey, wlio con- 

 tirmed Kowalevsky's and Seeligerfs statements, having. at 

 the same time, carefuUy studied the formation of the bran- 

 chial stigmata. a subject upon which I shall oidy touch 

 incidentally. Willey examined Ciona intestinalis and Cla- 

 velina lepadiforinis. He says (66. p. 338): „From obser- 

 vations made on Ciona intestinalis and Clavelina lepadi- 

 formis, I can confirm Kowalevskij and Seéliyer in saying 

 that tlie atrial cavities of Ascidians are derived essentially 

 from ectodermic invaginations; and that tiie idea that the 

 visceral wall of the atrium is derived from the hypoblast, 

 as put forward l)y van Beneden and, Julin, is entirely 

 without foundation.-' As mcntioned in my papor (31. p. 

 592). I have had an opportunity of stiulying Willeys pre- 

 parations, and liavo no doulit as to their decisive impor- 

 tance to the question It was, liowever obvious to me that 

 under the difficulties of investigatiou, circumstances may 

 easily be misunderstood. If W>lley\s fig. 28 on Pl. XXXT 



*) As Seeliger has thought it nccossary to state that in a ijrelimi- 

 nary communication T have X'cprescnted van Beneden and Julin 

 as champions of the theory of the formation of the peribranchial 

 cavity from tho ectoderni, a perusal of my detailed paper niay 

 convince hiin tliat this is not founded upon any „Irrthum-'. 

 As the inner vesicle of the Botryllus bud is formed from the 

 parietal layer of the peribranchial cavity, the Botryllus bud is 

 also, according to i-an Beneden and Julins investigations, an 

 ectodermal formation. My only object in discussing the litera- 

 ture on the subject of the peribranchial cavity, was to demon- 

 stratc this. 



