32 



gaaende enkelte divergerende detailler henviser jeg her 

 alene for oversigtens skjdd til mine tidligere bemerkninger 

 til de nævnte arbeider ,(31, pag. 613 ffg ; 33, pag. 218). 

 Som man kan forståa, kakler Pizon knoppernes indre blære 

 for entodermal. da han anser larvernes peribranchialsæk 

 for en udbugtning af tarmen (Se kap. I). 



Nervesystemet dannes efter Pizon som en fin nerve- 

 streng, der vokser ud fra moderdyret ind i knopperne, et 

 forhold, som forfatteren dog ikke formaaede direkte at iagt- 

 tage, og som ikke har faaet nogea bekræftelse af nogen 

 senere forfatter. Det samme gjælder 01;as mening, at en- 

 kelte ektodermcoller skulde løse sig fra epidermis og vandre 

 hen til dorsalrøret og her ved dettes underside danne 

 gangliet. 



Sammen med Frk. Bonnevie har jeg siden undersøgt 

 en SarcohotryUide, der udmerkede sig ved særdeles store 

 yderst fordelagtige knopper og her fandt vi de smukkeste 

 overgangsstadier fra det encellede dorsalror til gangliets 

 afsnoring fuldt overensstemmende med mine figurer Pl. 38, 

 fig. 25 — 30. Ogsaa hos talrige andre grupper er denne 

 gangliets dannelsesmaade bleven bekræftet af senere forfat- 

 tere, specielt Bitter og Caidlery (se nedenfor) og i den 

 allerseneste tid har Lefévre undersogt Bo/r;/??H.';-knopperne 

 paany og fuldstændig beki-æftet min opfatning. Han siger 

 (42. pag. 77): ,,I might also state that my sections entirely 

 confirm Hjorfs description of the formation of the ganglion, 

 and directly contradict P?^o /i's stateraent, that the constric- 

 tion of the ganglion from the dorsal tube cannot be estab- 

 lished". Han giver ogsaa herfor figurer, som paa det 

 noieste stemmer med mine præparater. En lignende beskri- 

 velse er ogsaa nylig given af Ritter for Goodsiria, der til- 

 hører gruppen Poli/styelidæ (50). Knopskydningen er ogsaa 

 her ,.palleal'' og dorsalrøret dannes som hos Botrylhis. 

 For Botryllidernes vedkommende turde derfor dette sporgs- 

 maal nu være uddebateret, og dermed synes mig et særdeles 

 vigtigt embryologisk problem lost. 



Distaplia magnilarva. 



For denne gruppes vedkommende henviser jeg til den 

 foregaaende afhandling af Bonnevie, der indeholder en nær- 

 mere oversigt af litteraturen specielt KoivaIevsky's og Sa- 

 JensJ{y's tidligere undersogelser. 



De selvstændige undersøgelser, som jeg har anstillet 

 sammen med Frk. Bonnevie, og hvis resultater er offentlig- 

 gjort i en forelobig meddelelse (34), bekræfter helt ud Ko- 

 walevskys ældre arbeide (38). 



Allerede af Della Vcdles ældre afhandling (13) er det 

 bekjendt, at knoppens indre blære afsnores fra tarmtraktus. 

 I kap. 2 beskrev jeg under henvisning til fig. 9, pl. XII, 

 hvorledes de smaa knopper dannes.*) 



*) Ifølge de nyere undersøgelser af Julin (se pag. 21) dannes knop- 

 pernes indre blære fra et epicardium, en dannelse vi ogsaa har 

 fundct hos knopperne (se Pl. IX. fig. "J — i:!). 



divergent details, I will only refer, for the sake of the 

 survey, to my previous remarks on the above works (31, 

 p. 613, etc; 33, p. 218). Pizon. as will be easily under- 

 stood, calls the inncr vesicle of the bud endodermal, as he 

 considers [the larvas peribranchial cavity to be an evagi- 

 nation of the intestine (see Chapter I). 



According to Pizon, the nervous system is formed in 

 tlie shape of a fine nerve cord, growing out of the parent 

 animal into the bud, a circumstance, however, which he 

 did not observe directly, and which lias not received con- 

 firmation from any subsequent writer. The same remark 

 applies to Oka's theory that certain ectoderm cells detached 

 themselves from the epidermis, and passed into the dorsal 

 tube, on the under side of which they formed the ganglion. 



Together with Miss Bonnevie, I have since examined 

 a Sarcobotryllid which was distinguished by the unusually 

 large size of its buds, which afforded very favorable con- 

 ditions for examination. Here we found most perfect tran- 

 sition stages from the single-celled dorsal tube to the con- 

 striction of the ganglion, agreeing fully with my figures, 

 Pl. 38, figs. 25 — 30. In numerous other groups too, the 

 manner of this ganglion's formation has been confirmed by 

 subsequent writers, especially Ritter and CanUery (see be- 

 low); and quite recently Lefévre has re-exarained BotryUus 

 buds. and fully confirmed my theory. He says (42, p. 77) : 

 ,,I might also state that my sections entirely confirm 

 HjorVs description of the ganglion, and directly contradict 

 Pizo)i.'>- statement that the constriction of the ganglion from 

 tlie dorsal tube cannot be established." He also gives 

 figures for this, which exactly agree with my preparations. 

 A similar description has also been lately given by Ritter 

 of Goodsiria, wiiich belongs to the group Pohjstyelidæ (50). 

 The budding here too is pallial, and the dorsal tube is 

 formed as in Botrylhis. This question, therefore, as far as 

 BotrylJidce is concerned. niay be considered sufficiently de- 

 bated, and thereby, as it seenis to me, an exceedingly 

 important embryological problem solved. 



Distaplia magnilarva. 



As regards tliis group. I would refer to the preceding 

 paper by Bonnevie, which contains a detailed survey of 

 the literature, especially Kowalevskys and S(densky's earlier 

 investigations. 



The investigations which Miss Bonnevie and I Iiave 

 pursued, the results of whicli have been publisiied in a 

 preliminary statement (34) fully confirm KotvaIevsky's older 

 work (38). 



It was already known from Della VaUe's older trea- 

 tise (13) that the inner vesicle of the bud is constricted 

 from the intestine. In Chapter II, I described, when 

 referring to Pl. XII, fig. 9, bow the small buds were 

 formed. *) 



*) According to Julin's later investigations (see note p. '21), the 

 inner vesicle of the buds is formed from au epicardium, a for- 

 mation which we also have found in the bud (see Pl. IX, figs. 

 9—13). 



