96 



Tal). XIII. Fig. 39. 40, a. L dette Belte, der er Binde- 

 vævslaget, iagttoges paa et temmeligt udviklet Embryo, der 

 forresten endnu laa indesluttet i Ægget, enkelte nedsænkede 

 Ectoderrnceller, samt i Eetodermet spredte, smaa, glindsende 

 Kalkkorn og enkelte Aabninger for udfaldne Spikler, 

 Tab. XIII, fig. 4o. h. Kowalevsky og Marion have obser- 

 veret, at Spikeldannelsen foregaar indeni selve Ectoderm- 

 cellerne, hvilket ikke har været muligt for mig at konstatere. 



Allerede hos det ganske unge Embryo, der i Regelen 

 havde en oval Form, saaes Midtpartiet at være meget 

 mindre opakt end Peripherien. og i den ene Ende iagt- 

 toges en liden Indsænkning af Eetodermet, Tab. XII. 

 Fig. 61. Paa Tversnit af et saadant Embryo viste der 

 sig indenfor Endodermet en begyndende Mund og rn Hule. 

 hvori laa Blommekorn, altsaa en Gastrula: paa ældre Em- 

 bryoner viste der sig en tydelig Gastrulamund, omgiven af 

 Celler. Tab. XII. fig. 68 — 70, ligesom der kunde iagttages 



Antydninger til Skillevægs 



Tab. XIII. fig. 4d. r. 41, a. 



Med Hensyn til disse tinder man her den samme tnærke- 

 lige Udviklingsmaade, som Kowalevsky og Marion har paa- 

 vist at tinde Sted hos Clavularia petricola, hvor der, førend 

 Mund og Svælg it dannet, sees i Hunden at Mavehulheden 

 indtil 26 Skillevæggé. Saasn&rt Svælget er dannet, for- 

 mindskes Antallet, indtil det regulære bliver tilbage. Hos 

 de tre Artci' af Slægten Xephthva. som ovenfor ere be- 

 skrevne, fandtes Embryonerne, paa nogle fan [Jndtagelser 

 mer. indesluttede i Ægget; intet Svælg var dannet hos 

 nogen af dem. selv ikke Ims de enkelte, der havde forladt 

 Ægget, men fra Mavehulens Væg udgik hos de mest ud- 

 viklede en Mængde Skillevæggé, som ragede langt ind i 

 Hulheden. Tal,. XIII. Fig. 40. 41. Disse Skillevæggé, 

 Mesenterier, bestode af en gelatinøs, halvgjennemsigtig 

 Masse, afsondret af begge Kimbladene med Fundamental- 

 membranen som Støtte og vaie beklædte med et Endothel, 

 Tab. XIII. fig. 41. b. dannet af Endodermcellerne. Paa 

 det mest udviklede Embryo, der laa frit i Mavehulheden, 

 Tab. XII. Fig. 7<). havde Ectodermcellerne, især omkring 

 Mundpartiet, antaget en meget langstrakt Form og vare 

 forsynede med lange Cilier, Tab. XIII. Fig. 42. 



Ligesom Udviklingen var den samme hos alle 3 

 Arter, saaledes var ogsaa Embryonernes Form den samme: 

 kun Spikelformerne viste sig noget forskjellige. I Be- 

 gyndelsen var Embryonet noget kantet. Tab. XII. Fig. 61, 

 senere blev det ægformet og var meget tidligt beklædt 

 med Cilier, Fig. 62. Naar den ovale Form blev nogel 

 mere langstrakt, saaes hist og her enkelte Spikler i Eeto- 

 dermet; kun paa Midten laa de noget tættere sammen, 

 forresten vare de overalt yderst spredte, enkelte vare meget 

 smaa. saa de vanskelig kunde maales. saaes kun med meget 



was seen. on transversal section, a narrow, hyaline. gelatin- 

 ous stripe, whieh was infallibly excreted from the ectoderm 

 cells and had pushed the fundamental membrane inwards 

 (Pl. XIII. figs. 3 ( J. 4d. a). In this stripe, whieh is the 

 connective tissue laver, there was observed upon a pretty 

 well developed embryon whieh, otherwise, lav. still enclosed 

 in the ovum, a few deeply embedded ectoderm cells. and 

 in the ectoderm. scattered, small, shining calcareous grains, 

 and a few gaps left by spicules fallen out (Pl. XIII, 

 fig. 40. b). Kowalevsky and Marion have remarked that 

 the spicular formation takes place inside the ectoderm 

 cells themselves, but this it has been impossible for me to 

 confirm. 



Already in the quite young embryon whieh. as a rule, 

 had an ovate form, the mesial part was observed to be 

 much less opaque than the periphery, and in the one ex- 

 tremity a small depression of the epiblast was observed, 

 (Pl. XII. fig. (il i. In the transversal section of such an 

 embryon, inside of the hypoblast, a rudimentary oral aper- 

 ture, and a cavity in whieh lav yoke-grains, showed 

 themselves — a gastrula therefore. In older embryons. a 

 gastrula aperture surrounded by cells showed itself (Pl. XII. 

 figs. 68 — Ti») whilst, also, indications of the divisional walls 

 COldd be oliserved (Pl. XIII. figs. 40, <: 41. a). With 

 regard to these, we tind. here, the same remarkable mode 

 of development whieh Kowalevsky and Marion have pointed 

 mit take- place in Clavularia petricola, where, previous to 

 the formation of the ma! aperture and gullet, as many as 

 26 divisional walls are seen at the bottom of the ventral 

 cavity. As soon as the gullet is formed, the number be- 

 comes diminished, until only the usual number rema ins. 

 In both the two species of the genus Nephthya whieh are 

 aliove described, the embryons were found, witb a few 

 exceptions, enclosed in the ovum: no gullet was formed in 

 any of them, not even in the few that had abandoned 

 the ovum. but from the wall of the ventral cavity in the 

 most developed ones, numerous divisional walls proceeded, 

 and these stretched far into the ventral cavity iPl. XIII, 

 ligs. 4(i. 41). These' divisional walls (mesenteries) consisted 

 of a gelatinous. semitransparent, substance, excreted from 

 both the epiblast and hypoblast, with the fundamental 

 membrane as support, and were clad with an endothelium 

 (Pl. XIII, fig. 41. /-) formed by the endodermic cells. On 

 the most developed embryon, whieh lav loose in the ventral 

 cavity (Pl. XII. fig. 70), the ectoderm cells. especially 

 about the oral portion, had assumed a very elongated form, 

 and were furnished with long eiliæ (Pl. XIII. fig. 42). 



Just as the development was. in the 3 species. the 

 same. so also was the embryonal form the same: the spicular 

 forms alone showed themselves to be somewhat different. 

 At the commencement, the embryon was somewhat angular 

 (Pl. XII. fig. 61), subsequently it became oviform, and vas 

 ver\ early covered with eiliæ (Pl. XII. fig. 62). When the 

 oval form became somewhat more elongate, a few spicules 

 were seen. here and there. in the ectoderm, and only in the 

 middle did they lie somewhat closer together, otherwise. 

 they were, everywhere, extremely scattered; a few were so 



