34 



diT, idet dell skyver Ektodermen foran sig, danner en For- 

 hoining paa Overfladen". Senere (7o) liar han dog forladt 

 dette Standpunkt, da lian ved nye Undersogelser har fundet 

 de tidligste Stadier af Gonoforernes Udvikling; og af disse 

 hans Undersogelser iVemgaar det, at Generationscellerne 

 hos MyriotJiela, som hos Tuhularidac, opstaar i Ektoder- 

 men, og at Gonoforerne dannes under Anlæg af en Ekto- 

 dernial „Glockenkern". 



Som jeg nedenfor skal vise. bekræfter mine Resultater 

 Korofneffs Opfatning. og sandsyidigvis har Alhiiaii ikke 

 seet de tidligste Stiulier af Udviklingen. 



AlJmans og Koroinejfs Udtalelser gjælder M. cocksii : 

 nuMi det ser ud. som om Udviklingen af Gonoforerne sker 

 paa snrame Maade hos alle M // f iofh ela- Arter. 



Ved Undersogelse af fuldt udviklede Gonoforer vil 

 man finde, at de fuldstrendig ligner de pseudomedusoide 

 Gonoforer, som ellers forekommer hos Slægten Lawpra. 

 Gonoforernes Væg dannes af Icun to Cellelag, af hvilke 

 det ene staar i Forbindelse med Blastostylens Ektoderm 

 og det andet med dens Entoderm (Tal). UT, Fig. 6 e). 

 Under den Forudsætning. at Gonoforerne hos MyriotJiela 

 igrunden er af samme Xatnr som de, der tindes hos 

 Lavipra, (hvis Udvikling jeg tidligere havde studeret, og som 

 ligesom de almindelige medusoide Gonoforer anlægges ved 

 Dannelse af ,,Glockenkern"), søgte jeg, paa Serier af Snit 

 gjenneni en stor Mængde Blastostyler, efter det allerførste 

 Anlæg til Gonoforerne. Længe fandt jeg intet, der kunde 

 stotte denne Opfatning, overalt fandtes en Ansamling af 

 Generatioiisceller liggende i Entodermen og uden nogen 

 Sammenhæng med Ektodermen, saaledes som ogsaa ,4//- 

 Dians Afbildninger illustrerer Forholdet; men ved Under- 

 søgelserne af meget unge Blastostyler. fandt jeg tilslut Uere 

 Exempler paa, at det tidligste Anlæg af Gonoforerne sker 

 ved Dannelsen af en ..Glockenkern", og at altsaa Genera- 

 tionselenienterne hos ilyriotliela som hos Tulmlariderne 

 har sin Oprindelse i Ektodermen. Efter min (_)pfatning 

 sker Dannelsen af Gonoforer i)aa følgende IMaade: 



Paa det Sted, hvor en Gonofor skal anlægges, bugter 

 Støttelamellen og Entodermen sig noget ud, idet den sam- 

 tidig aftager i Tykkelse og Fasthed. Ektodermen, som 

 overalt paa Blastostylerne er meget tyk og kompakt, giver 

 kun lidet efter for det fra Entodermen øvede Tryk, og paa 

 Blastostyler nes Overflade ser man endnu længe intet Spor 

 af Forandring (Tab. III. Fig. G a). 



Ved Toppen af Entoderniforhoiningen. hvor Støtte- 

 lamellen er tyndest, sker nu en Indvandring af Ektoderni- 

 celler i Entodermen (Dannelsen af ,.Glockenkern-'), men 

 paa samme Maade som hos de pseudomedusoide Gonoforer 

 (se ovenfor side 18) løsner disse Celler sig helt fra For- 

 bindelsen med Ektodermen og hele Cellehoben vandrer ind 

 i Entodermen, hvor den lindes liggende som AJhnans 

 ,,goiiogenetic chamber", og har givet Gruiid til den Op- 

 fatning, at disse Celler egentlig er Entoderniceller (Tab. 

 III, Fig. 6 b-d). 



pushes the ectoderm before it. produces an elevation on 

 the surface". Subsequently |73). liowever, he forsakes this 

 standpoint. liaving discovered. upon fresh investigations, 

 the earliest stages in the development of the gonophores. 

 It appears from tliese investigations, that the generative 

 cells in Myriotliela. as in Tiibularidæ, originate in the 

 ectoderm, and tliat the gonophores are fornied during the 

 formation of an ectodermal ..glockenkern". 



The results »( my investigations, as I shall show later 

 on. confirm KuroineJf"s view. Allmaii has prolial.ily not 

 seeii the earliest stages in the development. 



The remarks of AUma» and Korotneff have reference 

 to M. cocksil, but it seems as if the development of the 

 gonophores takes place in the same manner in all species 

 of Mi/riotJiela. 



An examinatioii of fully-developed gono[)hores will 

 show that tiiey bear a perfect resemblance to the jiseudo- 

 medusoid gonophores of the genus Lanqjra. The wall of 

 the gonophores is fornied of only two cell-layers. one of 

 which is counected witli the ectoderm. and the otlier with 

 the endoderm of the blastostyle (Pl. III, fig. G e). Upon 

 the sup[K)sition that the gonophores in Myrioihela are 

 really of the same nature as those in iMmprn, (whose deve- 

 lopment I had previously studied, and which, like the ordi- 

 n:ia'y medusoid gonophores, commence with the formation 

 of the ,.glockenkern''), I sought, in series of sections tlirough 

 a large number of blastostyles. for this earliest rudiment 

 of the gonophores. For a long time I could find nothing 

 to support this view; there were always accumulations of 

 generative cell.s lying in the endoderm. and quite uncon- 

 neeted witb the ectoderm. just as AUrnaiis illustrations 

 show. But on exaniining very.young blastostyles. I at last 

 found several instances of tlie formation of the earliest 

 rudiment of the gonophores tlirough a „glockenkern", and 

 that thus the generative products in MyriofJwla, as in Tu- 

 hidaridæ, originate in the ectoderm. The formation of the 

 gonophores takes place. in my opinion, in the following 

 manner: 



At the place where a gonophore is to be formed, 

 the structureless laraella and endoderm bulge out, at the 

 same time decreasing in thickness and firmness. The ecto- 

 derm, which all over the blastostyles is very thick and 

 compact. yields only slight to the pressure exerted upon 

 it by the endoderm; and for a long time no trace of a 

 cliange is discernible in the surface of the blastostyles 

 (Pl. III. Fig, Ga). 



At the toj) of the endodermal elevation, where the 

 structureless lamella is thinnest, an in-wandering of ecto- 

 dermal cells takes place (formation of the ..glockenkern"), 

 but, as in the pseudo medusoid gonophores {vide p, 18), 

 these cells beconie conii)letely detached from the edoderm. 

 and the whole cell-mass wanders into the endoderm, where 

 it is found lying as Allnuut'.-: ..gonogenetic chamber-. and 

 has given ground to the belief that these cells are in rea- 

 lity endoderm cells (Pl. III, fig. b-d). 



