13 



lul fra. at dette neppe kunde være miiligt, idt-t den alniin- 

 delig enibryologiske erfar/nr/, uanseet alle tbeorier. med stor 

 styrke taler for, at i nrerstaaende familier foregaar organ- 

 dannelsen eftei- ilet samme grundskemn. et ibrhold. som 

 viser den eiendommelige og fundamentale overensstemmelse 

 mellem æggene hos nærstaaende former. En eiendommelig 

 tilslutning har imidlertid Pizoii faaet i Garstcutrj, der (18, 

 pag. 12) sigei': ,.It certainly seems unjustifiable on the 

 part of Hjort to decline to believe Pizons statements on 

 the sole ground that in Phallusia and Clarel/ua the deve- 

 lopment of the peribranchial chambers takes place difte- 

 rently." At /'izoii selv ikke stiller sig paa samme stand- 

 punkt fremgaar tydelig (48 a, pag. b80), naar han forkaster 

 Willeys og mine undersogelser, fordi de ikke stemmer med 

 hans egne. skjent de gjaldt andre grupper. Pizoii siger 

 nemlig: ...Je doute beaucoup de lexactitnde de ces dernie- 

 res observations do Hjort et de W/llci/. bien que je n'aie 

 pas étudié les lai'ves de Dit:tci2)Iia et de Cioiia.-^ Dette PIzons 

 standpunkt er efter min opfatning ogsaa luldt berettiget 

 for en forsker, der føler sig overbevist om sine egne resul- 

 taters rigtighed; thi uden dette vikle den hele sammenlig- 

 nende udviklingshistorie alene blive en række beskrivelser 

 af enkelte arters udviklinger. At en sammenligning og en 

 slutning fra den ene familie til den anden er tilladt, be- 

 styrkes ogsaa af den hele udviklingsliistoriske erfaring. 



Hvorledes Garstarifi ud fra sit standpunkt formaar at 

 skrive en generel oversigt over den hele ..Budding in Tuni- 

 cata". og der forkaste mine resultater som ..manifestly im- 

 probable-'. naar han selv overhovedet ikke har undersøgt 

 nogen gruppes knopskydning. overlader jeg til ham at be- 

 svare. End eiendonnneligere bliver det, at han anfører det 

 forhold, at peribranchialsækken hos Botryllus skal være 

 ektoderninl og hos Clavelina og Phallusia entodermal for at 

 bevise, at knoppernes indre bkcre altid er entodermal, og 

 for hermed at ^tottc l-riiihhtdhrren! Er dette forhold rig- 

 tig, saa er vel det det haardeste stod, der nogensinde er 

 rettet mod kimbladlæren og, som vi siden skal se, ganske 

 anderledes afgjorende end knopudviklingen. Thi kimblad- 

 læren gjælder larreriies udvikling, og at forskjellige kim- 

 blade kan knopskyde viser ikke. at larveudviklingen er for- 

 skjellig, men kun, at kimbladcne maa opfattes paa en be- 

 stemt udviklingsmekanisk maade. 



Er det derfor rigtigt, at peribranchialsækken hos de 

 tbrskjellige familier af Ascidierne har en forskjellig dan- 

 nelse, saa er dette et saa theoretisk vigtigt punkt, at det 

 kræver den omhyggeligste og fornyede bekræftigelse, selv 

 om det er undersøgt af en saa fremragende forsker som 

 Pizon. Ingen vil derfor mere anbefale at dette sker end 

 forfatteren. Forelobig forekommer det mig berettiget at 

 udtale, at særdeles talrige undersogelser af dygtige forskere 

 afgjørende taler for, at peribranchialsækken er en ren eldo- 

 dermal dannelse, saa meget mere som CauMery (9) nylig 

 har offentliggjort undersogelser i samme retning, hvor han 

 bekræfter dette for grupperne: ..DisfapHa rosea, Leptocli- 

 nuni yelatinosum, Glo^sophorum lateiim, og Circinalhan con- 



take it for granted that this could scarcely be possible. as 

 general embryological experience, apart from all theories, 

 goes to show very clearly that in nenrly-allied families, the 

 formation of the organs talies place acrording to one funda- 

 mental i>lan, a eircumstance which shows the peculiar and 

 iundamental conformity between the ova in nearly-allicd 

 forms. Pizon, however, has gained one peculiar adherent 

 in Garstaiif/, who says (18, p. 12): ,.It certainly seems 

 unjustifiable on the part of Hjort to tlecline to believe 

 Pizons statements. on the sole ground that in Phallusia 

 and Chirclina the development of the peribranchial cham- 

 bers takes plnce differently." That l'izou himself does not 

 ahvays take up the same stand-point. is clear (48 a. p. 38Uj 

 when he rejects Williys and my investigations, because 

 they are not in harmfniy with his own, although they liad 

 reference to other groups. Pizon says: ...Je doute beau- 

 coup de lexactitude de ces deruicres observations de Hj(nt 

 et de Willey, bien que jo n*aie pas étudié les larves de 

 Distaplia et de C/o;»/." This stand-point of Pizons is. in 

 my opinion, fully justitiable in an investigator who feels 

 convinced of the correctness of his own results; for without 

 that. the whole developmental history would ouly be a series 

 of descriptions of tho development of certain species. The 

 justitiableness of taking a comparison and a conclusion from 

 one family ibr another is strengthened. too. by all develop- 

 mental-historical experience. 



How Garstang is able, from his stand-point tu write 

 a general survey of the whole „Budding in Tunicata". and 

 there reject my results as ..manifestly improbable", when 

 he himself has not investigated the budding of any groups 

 at all. I leave hini to say. Yet more strange is it that 

 he quotes the circumstance that the peribi-ancbial cavity in 

 Botryllns is ectodermal. and in Clurelina and Pindlnsid, 

 eiidodcrmal. in order to show that the inner vesicle of the 

 bud is always endodermal, and thereby to sapport the yerni- 

 luyer tin or//! If this fact is correct, it is probably the 

 hardest blow that has ever been directed against that 

 tlieory. and. as we shall presently see. far more decisive 

 than the development of the bud. For the germ-layer 

 theory has reference to the development of the larva, and 

 the IVict that different germ.layers can bud. does not prove 

 that the larval development is different, hut only tliat the 

 germ-layers must be considered in a decidedly develoinnen- 

 tal mechanical way. 



If. therefore. it is true that the peribranchial cavity 

 in the different families of Ascidire has a different forma- 

 tion, this is, theoretically, such an important point that 

 it requires renewed and most careful confirmation. even 

 if it has been investigated by so eminent a naturalist 

 as Pizon. No one, therefore. will more varmly advo- 

 cate this than the present writer. In the mean time, 

 I feel justitied in expressiug my opinion that the great 

 number of investigations by able anatomists speaks in favour 

 of the purely ce'odermal Jo)')iiati(ni of tin' perihrarnhial 

 cavity, the more so as Caullery (9) has recently published 

 investigations in the same direction, in which he conrirms 

 this for the groups ,,Distaplia rosea, Leptoclinum gelatina- 



