102 



Bindevævslag, hvori Spiklerne ere indleirede. Fig. 44, &; 

 men de Hulheder, hvori Spiklerne ligge, ere forsynede med 

 Ectodermceller, Fig. 44, c, der som oftest omslutte Spiklerne 

 saa intimt, at de gjerne følge med dem, naar de fjernes. 

 Indenfor Bindevævet er det almindelige Muskellag, der be- 

 klædes af et Endothel, dannet af et Lag runde Celler med 

 Kjerne og Kjernelegeme, Fig. 44, d, hvilket Endothel ogsaa 

 tapetserer Septa og Svælgets ydre Flade, Fig. 44, e. 



Hvad der især maa tiltrække sig Opmærksomheden, 

 er Svælgets særegne Bygning, som nu nærmere skal be- 

 skrives 1 . Strax nedenfor Mundaabningen begynder paa 

 Bugsiden Svælgrenden, der har en oval Form og strækker 

 sig lige ned til Svælgets frie Ende, Fig. 44, /. Saavel 

 Svælgrenden som den øvrige Del af Svælget er beklædt 

 med Epithel; men medens Svælgrendens Epithel dannes af 

 meget lange, smale Celler, der ere forsynede med Kjerne 

 og Kjernelegeme, og som have paa deres fri Ende en lang 

 Pidsk (Cilie), Fig 44, g, dannes den øvrige Del af Svælg- 

 epithelet af kortere Celler med almindelige Cilier, ligesom 

 der i dette Epithel er indleiret kolbeformede, encellede 

 Slimkjertler, Fig. 44, h. 



Strax ovenfor Svælgrendens Begyndelse udgaar i en 

 skråa Retning fra høire Væg, nærmere Rygsiden, et liste- 

 formigt, ovalt, omtrent 2 mm langt Fremspring. Dets øverste 

 Del er meget høit, tykt og rager langt ind i Svælget mod 

 dettes venstre Væg, Tab. XV, Fig. 13, a, men bliver alt 

 lavere og lavere, jo længere det strækker sig ned, Tab. XV, 

 Fig. 13, b. Det er dannet af en Fortykkelse- af Svælg- 

 epithelet, hvis Celler paa dette Sted antager en overordentlig 

 Længde, Tab. XIV, Fig. 45, a. Noget Bindevæv synes 

 ikke at være tilstede, derimod sees spredte Muskelfibre at 

 gaa over fra Svælgvæggen ind i Fremspringet. Lidt 

 nedenfor dette Fremspring sees et lignende, der ud- 

 gaar ogsaa fra høire Væg. men gaar strax over Rygsiden 

 til venstre Væg, hvor det antager næsten S-Formen og for- 

 længer sig næsten lige ned til Svælgets Ende. Opad ved 

 dets Begyndelse er dette Fremspring meget lavt og smalt, 

 Tab. XV, Fig. 13, c, men bliver høi ere og høiere jo længere 

 det strækker sig ned og rager da langt ind i Svælget, saa 

 at det naar dettes høire Væg, Tab. XV, Fig. 13, d. 



Disse mærkelige Fremspring synes a>t virke som 

 Klapper, der ikke godt kan have nogen anden Bestemmelse 

 end at lukke for Svælgrenden, hvorved Svælget i dets 

 største Længde deles i to Kanaler, saaledes nemlig, at den 

 ene Kanal kan virke som Spiserør, hvorigjennem Føde- 



1 For bedre at kunne orientere sig inddeler jeg Svælget i en 

 Bug- og Rygside, i en høire og venstre Side. 



broad, hyaline connective-tissue layer, in which the spicules 

 are entrenched . (PI. XIV, fig. 44, I), but the cavities in 

 which the spicules are placed are furnished with ectoderm 

 cells (PI. XIX, fig. 44, c) which, usually, inclose the spi- 

 cules so tightly that these often remain attached to them 

 when they are removed. Inside of the connective-tissue 

 layer, the usual muscular layer is found; this is covered 

 by an endothelium, formed of a layer of globular cells with 

 nucleus and nucleus body (PL XIV, fig. 44, d); this 

 endothelium also coats the septa and the gullets external 

 surface (PL XIV, fig. 44, e). 



What must attract special attention, is the peculiar 

 structure of the gullet, which I shall now describe more 

 particularly 1 . Immediately below the oral aperture, on the 

 ventral side, the gullet-passage begins; it has an ovate 

 form, and extends right down to the free extremity of the 

 gullet (PL XIV, fig. 44, f). The gullet-passage, as well as, 

 also, the remainder of the gullet, is clad with epithelium, 

 but whilst the epithelium of the gullet-passage is formed 

 of very long narrow cells, furnished with nucleus and nuc- 

 leus-body and carrying on their free extremities a long 

 whip (Cilium) (PL XIV, fig. 44, 'g), the remainder of the 

 gullet-epithelium is formed of shorter cells with the usual 

 ciliæ, whilst, also, there are entrenched in this epithelium, sub- 

 claviform, unicellular mucous glands (PL XIV, fig. 44, h). 



Immediately above the commencement of the gullet- 

 passage, there proceeds, in a diagonal direction, from the 

 dextral wall nearest to the dorsal side, a fillet-formed 

 oval protuberance about 2 mm in length. Its uppermost part 

 is very high and thick, and it projects far into the gullet, 

 towards its sinistral wall (PL XV, fig. 13, a), but becomes 

 less and less in height 'the further down it extends (PL 

 XV, fig. 13, b). It is formed by a tumefaction of the epi- 

 thelium of the gullet, whose cells, in this situation, acquire 

 an extreme length (PL XIV, fig. 45, a). There does not 

 appear to be any connective-tissue present, but, on the 

 other hand, scattered muscular fibres are seen to proceed 

 from the gullet-wall into the protuberance. Slightly below 

 this protuberance a similar one is visible, which, also, pro- 

 ceeds from the dextral wall, but passes immediately 

 across the dorsal side to the sinistral wall, where it almost 

 assumes the S-form, and becomes prolonged nearly right 

 down to the extremity of the gullet. Upwards, at its com- 

 mencement, this protuberance is very Ioav and narrow, 

 (PL XV, fig. 13, c) but becomes higher and higher the 

 further it extends down, and it then projects far into the 

 gullet, so that it reaches to its dextral wall (PI. XV, 

 fig. 13, d). 



These remarkable prominences appear to operate as 

 flaps, and they can scarcely have any other purpose than 

 to close the gullet-passage, causing the gullet, for the 

 greater part of its length, to be divided into two canals, in 

 such manner, that the one canal can serve as an alimentary 



1 In order to simplify the description, I divide the gullet, 

 into ventral and dorsal sides, and dextral and sinistral sides. 



