24 



erholder en anden udrilAingsrefninfj formnar at danne et 

 nyt individ. 



Er peribranchiulsækken hos Botrylliderne et ektoder- 

 inalt organ, saa kan saadant materiale findes hos begge 

 kiniblade, ja et kimblad (ektodermen) kan da alene danne 

 et nyt individ, som jeg allerede i tidligere arbeider udtrjdc- 

 kelig har fremhævet. Et saadant forhold berører kun den 

 lulriJdingsinekanisJie omfatning af kimbladcne (se Kap. 5); 

 det udsiger intet om den egentlige og vigtigste kiralaladlære, 

 at embryonaludviklingen overalt i dyreriget eller inden større 

 grupper følger de samme love i sine form- og organdan- 

 nelser. 



Efter min opfatning er derfor de støttepunkter, som 

 Pigon har anført for sin knopskydningstiieori endnu vanske- 

 ligere at bringe i overensstemmelse med kinibladlæren, end 

 den antagelse, at kimbiadene kan indeholde udifferentieret 

 materiale, der indeholder kræfter og materiale til nydan- 

 nelser; og linder- jeg endnu at kunne opretholde den opfat- 

 ning af det hele knopanlæg, som jeg i et tidligere arbeide 

 (31) har udtrykt saaledes: „Hos alle grupper dannes der 

 en tobladet blære og overalt danner den indre af de to 

 blade de samme organer, nemlig tarm, peribranchialsæk og 

 nervesystem. Men, som jeg har vist ovenfor, kommer den 

 indre blære hos Peropliora, Didenmum, Clavelina fra ento- 

 dermer, hos BotrylJus fra den ektodermale, larvale peri- 

 branchialsæk. Alene det faktum, at den samme indre blære, 

 som alene dannes af et af larvens kimblade, kan danne saa 

 forskjellige organer som tarm og nervesystem, synes tilfulde 

 at vise, at dette kimblad ikke maa opfattes saaledes som 

 det almindelig sker. Cellerne har meget mere en endnu 

 indifferent karakter, saadan som embryonahulviklingens bla- 

 stulastadinra har det; og dette indifferente cellemateriale 

 gaar over fra den ene generation til den andeu" (pag. 613). 



Med dette forhold for oie vil vi mere indgaaende be- 

 tragte knopanlæggets form og bygning hos de forskjellige 

 grupper. 



Paa Pl. IX til Pl. XI iiar jeg sogt at illustrere knop- 

 anlægget og knopskydningens forløb hos grupperne Pero- 

 pliora, BotnjUus, Distaplia, Amaroucium (Polgclinnm). 

 Pyrosoma. 



Pl. IX, tig. 1 gjengiver efter Koivcdevsky knojianlæg- 

 get hos Peropliora. Man ser her afbildet en gren af de 

 bekjendte stoloner, der bestaar af to cylindriske udbugt- 

 ninger. den ene omhyllende den anden. Den ydre er en 

 fortsættelse af moderdyrets epidermis og den har et tykt 

 lag cellulose hængende fast sammen med sine celler. Den 

 indre er en fortsættelse af moderdyrets epicardium. Den 

 danner skillevæggen i stolonen og Koivalevskys tversnit har 

 vist hvorledes denne skillevæg er en fra den ene side til 

 den anden afplattet dobbeltlaraelle, som man maa tænke 



ment and its course, but it sliows us only, that in the 

 germ-layers, — ectodcrm as well as endoderm, — there is 

 found, during development, material which ivJien hvoaglit 

 into other and neiv conditiom, wliere its development has 

 taJæn anotlier diredion, is eapahle of producing a new in- 

 dividual. 



If the peribranchial cavity in Botryllidæ is an ecto- 

 dermal organ, such material can be found in both germ- 

 layers, indeed, one germ-layer (the ectoderm) can then alone 

 form a new individual, a fact ui>on whicli I have already, 

 in ])revious papers, laid particular emphasis. Such a cir- 

 cumstance aftects only the derelopniental-meehaniral vieiv 

 of the germ-layers (see Chap. V); it asserts nothing con- 

 cerning the actual and most important germ-layer theory, 

 that the embryonic development throughout the animal 

 kingdom or within large groups, follows tlie same laws in 

 the development of its form and organs. 



In my opinion, there fore, the points which Pizon has 

 quoted in support of his budding theory, are vet more 

 difficult to bring into iiarmouy with the gei'm-layer theory, 

 tiian is the assnmption that the germ-layers may contain 

 undifferentiated material with power and material for new 

 formations; and I still feel justified in maintaining tiie 

 theory of the whole bud-development, which I have expres- 

 sed as follows in a former paper (31): ..In every group a 

 bi-laminar vesicle is forined, and the inner of the two 

 layers always forms the same organs, namely, tiie intostine. 

 the peribranchial cavity and the nervous system. But, as 

 I have shown above, the inner vesicle in Peropliora. Di- 

 demnum and Clavelina comes from the endoderm, in Bo- 

 tryllus, from the ectodermal, lai'val peribranchial cavity. 

 The very fact that the same inner vesicle, which is only 

 formed from one of the germ-layers of the larva, can form 

 such different organs as the intestine and the nervous sy- 

 stem, seems to show clearly tliat this germ-layer must not 

 be regarded in the oi-dinary way. The cells have, as yet, 

 a much more indifferent charactcr, such as in the blastula 

 stage of the embryonic development; and this indifferent 

 cell-material passes on from one generation to auother 

 (p. 613). 



With this circumstance in view, we will consider more 

 carefully the form and structure of the Inid-rudiment in 

 the various groups. 



On Pl. IX, Pl. X and Pl. XI, I have endeavoured 

 to illustrate the bud-rudiment and the course of budding 

 in the groups Perophora, BotryUas, Distaplia, Amarouriiinu 

 (Polyclinnm) and Pyrosoma. 



Pl. IX, fig. 1 reprodnces. after Koivalevsky, the ru- 

 dimentary bud in Perophora. A branch of the well-known 

 stolons is here represented, consisting of two eylindrical 

 evaginations, the one enveloping the other. The outer one 

 is a continuation of the parent-animars epidermis and has 

 a thick layer of cellulose firmly attached to its cells. The 

 inner evagination is a continuation of the epicardium of 

 the parent animal. It forms tlie septuni in the stolon, and 

 Kowalevshys transverse section has shown how this septum 

 is a double lamella flattened from side to side, and which 



