13 



mensmeltning af nerverørets forreste del med gjællesækken. 

 — Gangliet udvikler sig sterkt og dækker fuldstændig hypo- 

 fysen, som efterhaandon skrumper ind til et meget tyndt 

 i'Or, som ikke engang naar gangliets nederste kant. — 

 Nerverørets to sider/reiie mister sit hunen og omdannes til 

 et par ganske tynde nerver, som udgaar fra gangliets 

 nederste spids (fig. 30 — 32); deres forbindelse under ento- 

 dermroret svinder ogsaa ind til en tvnd cellesti"eng. 



Jeg iiar i min lieskrivelse af kuoppernes udvikling 

 iidelukkende tåget hensjm til den forst anlagte knop, altsaa 

 den distale i knoprækken. da organernes oprindelige anlæg 

 har været maalet for min undersogelse. — Jeg skal dog 

 tilslut ogsaa. med et ])ar ord berore udviklingen af de 

 proximale Icnopper i kjæden. 



Perihrancliialcaritetenie, der. som ovenfor beskrevet, 

 blev anlagt i moderdyret. for der egentlig kunde være tale 

 om nogen knop, strækker sig gjennem hele rækken og for- 

 deles ved indsnoring, ligesom ektodermen, cntodermrøret og 

 mesodermstrengen. paa de forskjellige knopper. 



De organer deriraod, som forst l)lev anlagt, efter at 

 knoppens afsnoring fra moderdyret var begyndt, deriblandt 

 nervesystem og tarmiradus, anlægges ogsaa i hver af de 

 proximale knojiper paa samme maade som i den distale. 



Resumé. 



1. Knoppens ydre blære bestaar fra torst af af hoie 

 cubiske celler, og den undergaar under knoppens ud- 

 vikling ingen forandringer, naar undtages dem, som 

 skjddes knoppens væxt; cellerne bliver paa de senere 

 udviklingsstadier noget lavere uden dog at gaa over til 

 pladecpithel, før mod slutten af knoppens udvikUng. 



2. Fra mesodermen anlægges iierirarclinm. eleoTÅad og de 

 sædvanlige mesodermale organer, generaiinusorqaner, 

 lUKskJfr. 0. s. v. 



3. Knoppens indre blære stammer fra moderdyrets endo- 

 styl og bestaar under de forste stadier af knoppens 

 udvikling af hoie cylinderceller. som senere bliver no- 

 get lavere. 



Fra knoppens indre liJære anlægges følgende or- 

 ganer : 



a. Feribraitdihdcavif eterne, som anlægges allerede i 

 moderdyret ved at en del af entodermrørets vægge 

 paa hver side bugter sig ud og lægger sig som et 

 blad ved siden af dette. De strækker sig gjennem 

 hele knoprækken ; men de afsnøres fuldstændig mel- 

 lem hver knop. medens entodermroret kun ind- 

 snevres. — Peribranchialcaviteterne spiller en stor 



as also the dorsal tuherde by the coalescing of the anterior 

 part of the nerve tulje with tiie branchial sac. The gang- 

 lion developes liuickly, aud completely covers the hypophysis, 

 wiiicii gradually shrinks into a very narrow tube, rea.ching 

 not even as far as the lower edge of the ganglion. The 

 two lateral ranii of tiie nerve tube lose their lumen, and 

 are transformed into two very thin nerves, issuing from 

 the lower end of the ganglion (figs. 30 — 32): their conuec- 

 tion beneath the endodermal tube also diminishes to a thin 

 celluhir cord. 



In my account of the development of the bud. I have 

 exclusively considered tiie first formed l)ud — the distal 

 one in the series of buds — , as the original incipiency of 

 the organs has Ijeen the aim of my investigations. Before 

 concluding, however. I will also, in a fcw words, touch upon 

 the development of tiie proximal huds in the chain. 



The perihrandual cavities, which, as already stated, 

 bad commenced to form in the mother animal before any- 

 thing like a liud was visible, extend thi-ough the whole 

 series, and are distributed by constriction among the diffe- 

 rent buds, as are also the ectoderm, tiie endodermal tube 

 and the mesodornial cord. 



On the other hand, those organs whieli (Hd not liegin 

 to form until after the process of separation of the bud 

 ironi the mother animal bad commenced — the nervoiis 

 system and the intestinal region, among others — , coni- 

 mence in each of the proximal buds in the same way as 

 in the distal. 



Recapituliitioii. 



1. The outer vesicle of the bud consists, from its com- 

 meneeraent, of high cubical cells. and during the deve- 

 lopment of the bud, undergoes no change hut such as 

 is oacasioned by the gi'owth of the Inid. In the later 

 stages of development, the cells liecome somewiiat lower, 

 without howevei' cbanging into fiattened epithelium 

 until tlie comiiletion of the l)ud's development. 



2. From the mesoderm are developed the pericardimu, 

 tlie elæoUast and the usual mesodermal organs, tlie 

 generative organs, inuscles, etc. 



3. The inner vesicle of the bud originates in the endo- 

 style of the mother animal, and during the earlier 

 stages of development consists of iiigh cylindrical cells, 

 which subsequently beconie somewiiat lower. 



From the inner residc of the i)ud are formed the 

 foUowiug organs: 



a. The perihrancliial carlties, wiiicii have already com- 

 menced in tlie mother animal by the evagination 

 of a part of tiie wall on eacli side of the endo- 

 dermal tube, and its disposition beside the latter 

 like a leaf They extend tlirougliout tlie series of 

 buds. Iieing. liowever, completely severed between 

 tlie buds, while the endodermal tulie is onlv con- 



