29 



tarmen har cndvidere de første gjællespalter dannet sig. 

 Tarmen er vokset betydelig og er naaet lien til kloaken. 

 Ingestionsaabningen er dannet ved sammenvoksning mellcm 

 gjælletarm og epidermis, egestionsaabningen ved sammen- 

 voksning af kloak (peribrancbialsækkens dorsale ]jarti) og 

 epidermis. Centralnervesysteraet viser sig nu som et bagtil 

 lukket, cylindrisk ror. der fertil nunider ud i gjælletarmen. 

 Paa fig. 3 hænger knoppen endnu tydelig sammen med 

 stolonen; denne forbindelse bliver væsentlig mindre i fig. 4, 

 der i det hele fremstiller de samme forhold som fig. 3, 

 men paa et noget ældre stadium. 



I den senere tid er knopskydningen hos PeropJinj-a 

 behandlet i 2 nye arbeider. Bitter har i en forelobig med- 

 delelse (5U) omtalt, at eentralnervesystemet efter lians un- 

 dersøgelser anlægges paa lignende maade, som af mig skil- 

 dret for BotrijUus vedkommende, og jivortil jeg skal komme 

 tilbage under denne gruppe. Derimod mener Lefhre. at 

 dorsaltuben. det fælles anlæg for centralnervesystem og 

 hypophysis. anlægges fra vandrende mesodermceller (42). 

 Han siger pag. 76: ,.Iu the anterior region of the bud a. 

 little to the left of the median dorsal line there is seen 

 a slender elongated mass of cells loosely grouped together 

 and lying against the outer surface of the inner vesicle". 

 Det var umuligt for Lejhre at finde nogen sammenhæng 

 mellem disse celler og den indre blære. Senere optræder 

 der et lumen i cellegruppen, den ordner sig til et epithe- 

 lium og afsnorer gangliet, som af mig beskrevet for Botri/l- 

 Z?(5-knopperne. 



Vi (ipsætter diskussionen af disse divergerende opfat- 

 ninger^til sidst i dette kapitel, etterat ogsaa andre grupper 

 er beskrevne. 



Lefirre mener ogsaa, at anlægget for pericardium og 

 iijerte hos Perophora anlægges fra mesodermceller imodsæt- 

 ning til den ovenfor skildrede fremstilling hos Koircdevsktf. 



Saavel Ritter som Lefhre har dernæst fundet, at 

 stolonens skillevæg ikke, som Koiudlershy skildrer det, for- 

 bliver i forbindelse med branchialsækken men med den 

 venstre halvdel af peribranchialsækken hos den unge knop, 

 saasnart den indre blære deler sig i 3 blærer. Begge for- 

 fattere anfører dernæst, at denne forbindelse hos knopan- 

 lægget med stolonernenes skillevæg snart løses. Naar Rit- 

 ter heraf drager den slutning, at dette beviser, at stolo- 

 nernes skillevæg hos Pero])hora ikke er at opfatte som 

 Ascidiernes epicardiura, da kan jeg heri ikke erklære mig 

 enig. Jeg maa her. som ved andre anledninger kræve, at 

 undersøgelser over Ascidieorganernes homologi maa løses 

 ved studium af Jarverne og ikke af knopperne, især ikke 

 de ganske unge knopper. Som man siden skal se. dannes 

 f. eks. efter min fremstilling hos i>ofr//?/H»--knoppen dorsal- 

 roret fra peribranchialsækken, hos i)/s^rtj)//fl-knoppen dan- 

 nes det derimod efter Bonnevies og mine undersogelser fra 

 den midterste af de 3 blærer, hvori ,.den indre blære" de- 



the brancliial-gut. the first branciiial stigmata have been 

 formed. Tlie intestine lias grown considerably. and reaches 

 to the cloaca. The branchial aperture is formed by 

 a coalescing of the branciiial gut and tJie epidermis, the 

 atrial aperture by the coalescing of the cloaca (the dorsal 

 part of the peribranchial cavity) and the epidermis. Tiie 

 central organs of the nervous system now appear as a 

 cylindrical tube, closed behiiid, and opening in front into 

 the branchial sac. In fig. 3, the bud is still distinctly 

 connected with the stolon; this connection lias become 

 considerably slighter in fig. 4, wiiich, on tlie wiiole, repre- 

 sents the same conditions as fig. 3. hut at a much later stase. 



In more recent times, the subject of budding in Pero- 

 phora has been treated of in 2 new works. Ritter, in a 

 ])reliminary account (50) has stated that the central organs 

 of the nervous system commence, according to his investi- 

 gations, in a similar \vay to that described by me in the 

 case of Botryllns, and to which I shall return under that 

 group. Lefi'vre, on the other hand. considers that the 

 dorsal tube. the conimon rudiment of the central organs of 

 the nervous system and the hypophysis. originates in wan- 

 dering mesoderm cells (42). On p. TG. he says: ,.In the 

 anterior region of the luul. a little to the left of the me- 

 dian dorsal line, there is seen a slender elongated mass of 

 cells, loosely grouped together. and lying against the outer 

 surface of tlie inner vesicle-. It was impossible for Lefévre 

 to find any connnunication between tliese cells and tlie in- 

 ner vesicle. Subseipiently a lumen appears in the group 

 of cells; they arrange themselves into an epiflielium. and 

 constrict the ganglion, as described by me in the case of 

 Botryllns buds. 



We will put off the discussion of tbese divergent 

 opinions until thi' conclusion of this chapter. when other 

 groups have also been described. 



Lefhre thinks too, that the rudiment of tlie pericar- 

 dium and heart in Perophora originates in the mesoderm 

 cells. contrary to KowaJevskys description given above. 



Both Ritter and Lejevre have then found that the 

 septuni of the stolons does not, as Kouulevshy described 

 it, reniain in connection with the branchial sac, but witii 

 the left half of tiie peribranchial cavity in the young bud; 

 as soon as the inner vesicle divides into 3. Xext. both 

 authors state that in the rudimentai'y bud. this connection 

 vvitli the septum of the stolons is soon broken off. When 

 Ritter draws hence the conclusion that this proves that the 

 septuni of the stolons in Peropliora is not to be interpreted 

 as the Ascidian"s epicardium. I cannot declare myself of 

 the same opinion. I would here. as on other occasions, 

 urge that (iiiestions regardiug the homology of the Ascidian 

 organs, must be solved by the study of the Jarvce. and not 

 of the buds, especially not of quite young buds. As we 

 shall presently see, the dorsal tube, for instance, according 

 to my statement witii regard to the Botryllns bud. is 

 formed from the peribranchial cavity. whereas in the Dista- 

 plia bud, it is formed, according to Bonnevies and my 



