16 



I et senere arbeide har Pizon (4t)) end skarjoere ud- 

 talt sin mening, idet lian hos Ascidia r/Uosa beskriver ej^i- 

 cardiet saaledes: ..Au moment de Tapparition des premie- 

 res fentes branchiales chez VAseidia villosa, ce sac" (epi- 

 cardiet) „est encore largement ouvert, dans la cavité 

 enterique de laqnelle il dérive. Chez Cynthiu moms Tepi- 

 carde se presente comme deux grands prolongements des 

 sacs ijeribranchiaux et rapelle ainsi trés-exactement la dis- 

 230sitiou, que je lui ai decrite chez les Botryllidés.-' Efter 

 Phon er altsaa hos Pol/zcliii/Dii og Ascidia riUosa epicar- 

 diet en udbugtning af entodermen (tarmtraktus). hos Bn- 

 iri/llus og Cijidhia morns derimod er peribranchialsækken 

 det organ, der danner epicardiet som to udbugtninger. 



Jeg har ovenfor saa iudgaaende behandlet disse me- 

 ningsforskjelligheder mellem Pizon og mig, ikke for at kon- 

 statere, hvem der har havt ret, men fordi en af aarsagerne 

 til den store diflerents mellem Pizons og min opfatning af 

 den hele udvikling beror paa dette punkt. 



\i saa i det foregaaende, at epicardiet (ifølge van 

 Benede)! og Jnlin og SeeJiger) hos Clavelina samt (ifolge 

 Maurice, KoivaJersl-y) hos Amaroucium utvivlsomt var en 

 direkte udbugtning af tarmtraktus. Det har ogsaa lykke- 

 des mig selv ved indgaaende undersøgelser at bekræfte dette. 

 Paa planche X hnder man en larve af Amaroiicium roseum, 

 tig. (j, samt et ungt dyr, pl. X, hg. 9, der netop har gjen- 

 nemgaaet metamorphosen og endnu ikke dannet nogen post- 

 abdomen. Paa tversnit lykkedes det mig her at konstatere, 

 at det cylinderformige epicardialror, som van Beneden og 

 JhIIii saa indgaaende har beskrevet det. nær tarmtraktus 

 deler sig i to ror, hvis epithelier umiddelbart fortsætter sig 

 i gjælletarmens. Der kan for denne families vedkommende 

 herom ingen tvivl næres; og maa jeg vel da være berettiget 

 til at slutte det sammen for ChweJinas og Peroplioras*') 

 vedkommende. 



I det foregaaende saa vi fremdeles, at de dannelser, 

 der af Pizon beskrives som epicardier, ogsaa var iagttaget 

 saavel af Oka (45) som af mig for BotrijUus vedkommende. 

 Der hersker altsaa ingen meningsforskjel angaaende de fak- 

 tiske forhold, kun angaaende tydningen af disse. Kau nu 

 disse peribranchialsækudvidelser hos BnfrylJus (og Cynihia 

 morns) „homologiseres-' med epicardialdannelserne hos Anui- 

 roncinin og Clavelina, som jeg har beskrevet dem ovenfor? 



Det forekommer mig. at dette ikke er muligt. Be- 

 tragter vi for det forste den morphologiske**) side af spoi'gs- 

 maalet, saa mna man vel indromme. at det er en væsentlig 

 forskjel for et organ, om det er en udbugtning af tarmtrak- 

 tus eller en udbugtning a f peribranchialsækken. Jeg vil 



*) Ritter (5n) meddeler, at hos en Perojihorakno]) forblev et af 

 peribranchialsækanlæggene i forbindelse med stoloiiens skillevæg. 

 idet knoppens indre blære delte sig i tre. Jeg advarer her mod 

 at bygge forstaaelsen af et organ paa knopskydningen, især hvor 

 Kowalevshy i andre tilfælde har konstaterot et andet forhold. 



**) Angaaende peribranehialsækkens dannelse i embryouahidviklin- 

 gen se ovenfor. 



In a later work, Pizon (49) expresses his opinion 

 more clearly, when he describes the epicardium in Ascidia 

 villosa as foUows: ,.Au moment de l'apparition des pre- 

 mieres fentes branchiales chez Y Ascidia villosa, ce sac" (the 

 epicardium) ,,est encore largement ouvert, dans la cavité 

 enterique de laquelle il dérive. Chez Cyniliia nnjrus Fépi- 

 carde se presente comme deux grands prolongements des 

 sacs peribranchiaux, et rapelle ainsi trés-exactement la dis- 

 position que je lui ai décrite chez les Botryllidés.-' Accor- 

 ding to Pizon. therefore. the epicardium in Polyclinniii and 

 Ascidi(( villosa is an evagiuation of the endoderm (the ali- 

 mentary canal), whereas in Botryllns and Cynfliia moras, 

 the peribrancliial cavity is the organ whicb forms the epi- 

 cardium in the shape of two evaginations. 



I have thus thoroughly discussed these diflérences of 

 opinion between Pizon and myself, not in order to jjrove 

 which is right, but because one of the reasons of the great 

 difference between Pizoris view of the whole development, 

 and my own, depends upon this point. 



We have already seen tliat the epicardium (according 

 to van Benede)! and Julin, and Seeliyer) in Clareli)ia, and 

 (according to Maurice and Koifcdevslaj) in A))Utroncium, is 

 without doubt a direct evagination of the alimentary canal. 

 By thorough investigations I have also succeeded in corro- 

 borating this. On Pl. X, fig. 6 will be found a larva of 

 Ainaroin-inm rosemn, (and on Pl. X, fig. 9) a young animal, 

 which lias just undergone metamorphosis, and has not yet 

 formed any post-abdomen. In transverse sections I suc- 

 ceeded in demonstratiug that the cylindrical epicardiac tube, 

 as van Beneden and Jid/n have so minutely described it, 

 divides, near the alimentary canal, into 2 tubes, whose epi- 

 thelia are continued directly in that of the branchial sac. 

 As far as this family is concerned, no doubt of this can be 

 entertained; aud I may therefore be justified in conchiding 

 the same with regard to Clavelina and Peropliora.*) 



We see in the above that the formations described 

 by Pizon as epicardia, were also observed by Oka (45) 

 and myself as far as Botryllns was concerned. No diffe- 

 rence of opinion therefore prevails as to the actual facts, 

 but only as to their interpretation. Can now these expan- 

 sions of the peribranehial cavity in Botryllns (and Cy)itliia 

 n!0)'!(s') be „homologised" with the epicardiac formations in 

 Aincuvncinm and Clareli)ia, as I have described them 

 above ? 



It seems to me that this is impossible. If, in the 

 first plaee. we look at the morphological**) side of the 

 question. it must be admitted that it is an essential diffe- 

 reuce in an organ, whether it is an evagination of the in- 

 testine, or an evagination of the peribranehial cavity. I 



*) Ritter (.')0) states that in a Perophora bnd, one of the rudiments 

 of the iieribranchial cavity remaiiied in connection with the wall 

 of the stt)lon, the inner vesicle of the bud dividing into thrce. 

 I would here titter a warning against basing the comprehonsion 

 of an organ on the budding, especially where Kowalerslcy in 

 other cases has proved a different state of the matter. 

 **) Concerning the formation of the peiibrancliial ca\-ity in the em- 

 bryonio development, see abovo. 



