27 



blære forholder sig som et passivt organ, der ikke kan uil- 

 viklc nogen nydannelser. 



I moderdyret viser derfor altid den forste begyndelse 

 til knopskydningen sig i det organ, der danner den indre 

 blære. 



Ovenstaaende figur viser saaledes, hvorledes de første 

 antydninger til knopskydningen hos Bofri/Uiderne begynder 

 dermed, at enkelte af peribranchials;«kkeTis flade epithel- 

 celler vokser i størrelse, de bliver forst eubiske, senere 

 cylindriske, og hele cellepartiet biigter sig nu halvkugle- 

 formig udåd, hvorved epiderniis skyves foran. Man vil da 

 let forståa, hvorledes efterhaanden det noget reldre stadium, 

 fig. 5, Pl. IX, fremgaar af ovenstaaende figur. 



En mere indgaaende forstaaelse af de forskjellige 

 deles betydning og raorphologiske værdi i knopanlægget, 

 kan imidlertid først forstaaes ved et studium af knoppens 

 videi'e udvikling. At give en fremstilling af dennes forløb 

 vil derfor være vor opgave i det følgende kapitel. 



Kapitel 3. 

 Orgaudaimelseii hos kiiopperiie. 



Et studium af litteraturen over Ascidiernes knopskyd- 

 ning viser, at næsten hver forfatter har sin egen fremstil- 

 ling. Specielt er opfatningerne over nervesystemets dan- 

 nelse særdeles forskjellige, og dette vanskeliggjør i høi grad 

 forsoget i^aa at give en samlet fremstilling af den hele ud- 

 viklingsproces. Af denne grund har jeg i mine tidligere 

 arbeider kun med faa ord anstillet sammenligninger, idet 

 jeg efterhaanden søgte at skaffe mig materiale til selvstæn- 

 dige erfaringer fra de forskjellige familier. Det har hidtil 

 lykkedes mig at studere grupperne Botr/jUus, Distaplia og 

 Pohjclinum samt tildels Peroplwra og Pyrosoma. Resul- 

 taterne af disse sammenlignende undersogelser har bestyrket 

 mig i den tro, at knopskydningen overalt foregaar paa den 

 samme maade og derfor overalt er den samme udviklingspro- 

 ces. Før jeg imidlertid gaar over til at give en skildring af 

 knopskydningen i sin almindelighed, vil jeg dels efter egne 

 undersogelser dels efter litteraturen gjennemgaa de vigtigste 

 grupper, og jeg begynder da med den form, som dannede 

 udgangspunktet for Koivahvslajs grundlæggende undersogel- 

 ser, nemlig Perophora listvri. Wiegni. 



Perophora. 



I Kap. 2 saa vi, at knopperne hos Peroplwra dannes 

 fra de lauge forgrenede stoloner. Under henvisning til 

 Pl. IX, fig. 1 skildrede jeg, at knopanlæggets indre blære 

 dannedes ved udbugtning af stolonens ,,skillevæg" (moder- 

 dyrets epicardium), og idet denne udbugtning foraarsagede 

 en Hgnende udijugtning af stolonens epidermis dannedes 

 knopanlægget i form af 2 blærer med vandrende mesoderm- 

 celler imellem dem. 



the formation of the organs in the l)ud. this important 

 consetjuenee, namely, tliat the outor vesicle remains as a 

 passive organ, whieh cannot develope any new formation. 



In the parent animal therefore, the earliest commence- 

 ment of budding always api)ears in the organ which forms 

 the inner vesicle. 



The above figure shows bow the first indication of 

 budding in BotrylUdæ is an increase in the size of a few 

 of the Hat ei)ithelium cells of the peribranchial cavity, 

 which become first culncal and tlien cylindrical, while the 

 whole cellular part bulges out in a hemispherical shape, 

 thereby jnishing the epidermis in front. It will then be 

 easily understood how by degrees tiie rather more advanced 

 stage in fig. G, Pl. IX, developes from the above figure. 



A møre thorough comprehension of the significance 

 of the different parts and their morphological value in the 

 rudimentary bud, can however, only be øbtained by a study 

 of the further development of the bud. It will therefore 

 be our endeavour to give an account of its course in the 

 next chapter. 



Chapter III. 

 The Formation of the Organs in the Bud. 



A study of the literature on budding in Ascidians 

 shows that nearly every author has his own theory. The 

 theøries on the formation of the nervous system in paiti- 

 cular are exceedingly varied, and this greatly enhances tiie 

 difficulty of an attempt to give a collected statement of 

 the whole developmental process. For this reason. I have, 

 in my previous papers, only drawn brief comparisons, endea- 

 vøuring by degrees to obtain material for independent 

 e.xperience from the different families. Up to the present, 

 I have succeeded in studying the grøups Botryllus, Dista- 

 plia, Pohjclinum and, to same extent, Perophora and Pij- 

 rosoma. The results of these comparative investigations 

 have strengthened me in the belief that budding always 

 takes place in the same manner, and is therefore always 

 the same developmental process. Before I proceed, how- 

 ever, to give a description of budding in general, I will go 

 through the most important groups, partly from my own 

 investigations, partly from literature, beginning with the 

 form which was the starting-point for Kowalershijs funda- 

 mental investigations, viz. Prropltora listeri, Wiegm. 



Perophora 



In Chai)ter II, we saw that the buds in Peropliora, 

 were fornieil from the long, ramified stolons. In directing 

 attentiou to Pl. IX, fig. 1, I described how the inner ve- 

 sicle of the incipient bud was førmed by evagination of 

 the wall of the stolon (epicardium of the parent animal); 

 and as this evagination oecasiøned a similar evagination of 

 the epidermis of the stolon, the incipient bud was førmed 

 in the shape of 2 vesicles, with wandering mesoderm-cells 

 between them. 



4' 



