Længere bagover luir den indre blære imidlertid iin- 

 dergaaet væsentlige forandringer, idet de tørste anlæg til 

 epicardier og tarm viser sig. Anlægget til epimrdiet be- 

 staar i at blærens ventrale og dorsale vieg, paa et lidet 

 stykke nær dens bagerste ende, og efter en linie, som fal- 

 der sammen med knoppens længdeakse, er smeltet sammen 

 og gjennenibrudt; herved er gjællesækken paa dette stykke 

 delt i to ror, som atter forenes ha.^ den dannede spalte, 

 og man vil paa tversnit her se i» mindre ringe istedetfor 

 den ene, som viste sig længer foran, medens man ved at 

 folge snitserien bagover vil rinde, at disse atter forener sig. 



Anlægget til fnrinkaiKilen viser sig som en blindt en- 

 dende udbugtning fra den indre liiærc dorsalt for det sted, 

 hvorfra epicardierne udgaar. 



Dette stadium er omtrent tilsvarende til det udvik- 

 lingstrin, som iS(deiiskij liar af bildet i fig. 32; men som det 

 fremgaar af min beskrivelse, er der paa tiere punkter man- 

 gel paa overensstemmelse mellem hans og vore resultater. 



Han beskriver her nervesystemet som et langt, tyndt 

 rør, der ligger tret ind til entodermen i næsten hele knop- 

 pens længde. Det lykkedes os ikke at finde noget tilsva- 

 svarende, skjont vi meget ondiyggelig undersogte, saavel 

 Ilegge blærer, som de raesodermelementer. der 1)efandt sig 

 mellem dem. Yistnok fandtes der flere steder smaa grup- 

 per af celler; men der var ingen intim forl)indelse mellem 

 dem, og de viste sig altid kun paa et eller et par snit, 

 saa vi maatte betragte disse ansamlinger som en tilfældig 

 sammenstillen af mesodermceller. 



I raodsætning til Sah-iisk/j har vi paa dette stadium 

 heller ikke fundet noget anlæg til perihrancliiidcaviteter. 

 medens tayin og epicardier er naaet til et lignende udviklings- 

 trin. Kun har vi fundet en sammenhæng mellem begge 

 epicardier i knoppens bagerste del, saa at epicardiedannelsen 

 viser sig som et U-formet ror, der med l)egge de aabne 

 ender niunder i den midtre blære, medens Salensky beskri- 

 ver den som to af hinanden nafhæna:ige udbngtninger. 



Stadium li. 



Det andet stadium, som jeg vil benytte til min frem- 

 stilling, har jeg illustreret ved en serie af tversnit (fig. 1 

 — 7) og ved et mediansnit (fig. 8). 



Paa dette ser man paa den indre blæres dorsale væg 

 en forover rettet udlnigtning, det første anlæg til nerve- 

 systemet (Dorsalroret). Paa tversnit viser denne ndbugtning 

 sig forrest som en ring (fig. 1). gaar dernæst over i den 

 indre blære (fig. 2) for endelig (fig. o] kun at vise sig som 

 en fortykkelse af denne. 



Dette anlæg til dorsalroret iios Distaplia viser en 

 paafaldende lighed med det samme anlæg hos Botrj/llus, 

 iivad man kan se ved at sammenligne fig. 8 med Hjorts 

 afbildning. (4), Tab. 36, fig. 20 



Farther back, however, the inner vesicle lias under 

 gone important changes, tiie first rudiments of epkxirdia 

 and intestine Iiaving appeared. The commencement of the 

 former consists in the fusion and l)reaking thi"ough of the 

 ventral and dorsal vvalls ot the vesicle, on a small jiiece 

 near its pcjsterior end. and in a line coincidina; vvith the 

 long axis of tiie bud. The brancliial sar on this piece is 

 thereby divided into two channels, which reunite beliind 

 the cleft formed. In a transverse section at this point, 

 two smalier rings will lie seen instead of the (Uic whicii 

 appeared farther forward, while, by foUowing the series of 

 sections backwards, it will be seen that these rings once 

 more unite. 



The rudimentary httestinal canal ajjpears as a lilind 

 protuljerance on tlie inner vesicle dorsal of the spot from 

 wliich tlie epicardia issue. 



Tliis stage as nearly as possible answers to tiiat whirli 

 iSalenshj has shown in his fig. 32, but, as will appear from 

 my description, there are several points in wlnch there is 

 a want of agreeraent l)etween his results and ours. 



Salenslx-y there describes the nervous system as a 

 long, narrow tube lying close to the endoderm through al- 

 most the entire lengtii of the bud. We did not succeed in 

 finding anything answering to tids, altliougli we examined 

 very carefully both the two vesicles and the mesoderm ele- 

 ments between them. It is true that in several places we 

 found small groups of cells. but there was no very close 

 connection between them, and they always appeared only 

 on one or on a couple of sections, so that we were obliged 

 to consider tliese accumulation as chance groupings of me- 

 soderm cells. 



We also ditfer from Salenskij in not finding, at this 

 stage, any indication of peribranchial rarities, while the 

 intestine and epicardia liave reached a simihir stage. We 

 have only found a connection between the two epicardia 

 in the posterior part of tiie bud, so that their formation 

 has the appearance of a U-shaped tube wiiose free ends 

 open into the middle vesicle. while Salenski/ describes them 

 as two protuberances quite independent of one another. 



Stage II. 



T have illustrated the second stage wiiich I shall 

 employ in my account, by a series of transverse sections 

 (tigs. 1 — 7) and one median section (fig. 8). 



On the last-named there is visible, on the dorsal wall 

 of the inner vesicle. an anteriorly directed protuberance, 

 the first rudiment of tlie iierrous system (the dorsal tube). 

 In transverse sections this protuberance appears as a rin;;: 

 (fig. 1), then passes into tlie inner vesicle (fig. 2) apjjearinsi 

 lastly as a thickening of that vesicle (fig. 3). 



This rudiment of a dorsal tube in Distaplia exiiiljits 

 a striking resemblance to that in BotrylJus. a resemblance 

 wliich may be seen by coniparing fig. 8 with Hjorts illu- 

 stration (4) Pl. 36, fig. 2U. 



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