90 



2 Par, som adskille sig noget fra de øvrige, nemlig Ret- 

 aingssepta, der svare til Mundvigene eller Gronidierne. 

 Septa staa her lrengere fra hinanden, hvorved Intraseptal- 

 rummet bliver større, Tab. XI, Fig. 3. 11 a, og Muskel- 

 anordningen er forskjellig, idet de transverselle Muskler 

 ere placerede paa den indre Flade, saa at de vende mod 

 hinanden og udfykle for en liden Del Intraseptalrnmmet. 

 Tab. XI, Fig. 3 a, iinedens de longitudinelle Muskler sidde 

 paa Skillevæggens ydre Flade og altsaa vende mod det 

 tilgrændsende Interseptalrum. Tab. XI, Fig. 3 b. Paa de 

 øvrige 4 Par Septa, Tab. XI, Fig. 3, 2, er Muskelanord- 

 ningen ganske modsat. De longitudinelle Muskler sidde 

 paa Skilleveggens indre Flade, vende mod hverandre i det 

 intraseptale Rum, Tab. XI, Fig. 3 c, imedens de transver- 

 selle Muskler indtage den ydre Flade. Tab. XI, Fig. 3 cl. 

 Ved Skilleveggenes Udspring i Physa ere hverken de longi- 

 tudinelle eller transverselle Muskler stærkt udviklede, men 

 de blive stærkere, alt eftersom de komme hengere op. 



De transverselle Muskler danne en Membran, der er 

 yderst tynd forneden, men opad imod Svælgrøret bliver 

 den tykkere og foldet, og udfylder for de 4 Septapars Ved- 

 kommende omtrent det halve Interseptalrum. De longitu- 

 dinelle Muskler ere langt stærkere end de transverselle ; 

 opimod Svælgroret tiltage de stærkt i Tykkelse og danne 

 en tyk Busk (Fane), der ganske udfylder Intraseptalru tu- 

 rnene, Tab. XI, Fig. 3 c, 11 b. Naar man gjør et Tver- 

 snit af Dyrets overste Del. ser det tid. som mn Svæluroret 

 er omsluttet af tykke, hvidgule Søiler, der ere Længde- 

 muskler i noget kontraheret Tilstand, Tab. XI. Fig. 10 o, 

 11 b. Samtlige fuldstændige Septa bære Mesenterialfila- 

 menter, som ere temmelig korte, proptrækkerformigt op- 

 trukne og strække sig kun et lidet Stykke nedenfor Svælg- 

 rørets nederste Del, i hvis Xærhed de udspringe, Lige ved 

 Randen af de longitudinelle Musklers Fane. Tab. XI. Fig. 

 10 a, 11 c 



Imellem hvert 2 Par af de fuldstændige Septa i Inter- 

 septalrummet er et Par sekundære, ufuldstændige Septa, tier 

 ogsaa tåge deres Udspring i Bunden af Physa, Tab. XI, 

 Fig. 8 «, 10 c, og ere her knapt en halv Millimeter brei le. 

 men blive snart smalere, idet de fortsætte sig opad. hvor 

 de sees som smale, listeformige Fremspring, der gaa lige 

 op paa Mundskiven. Tab. XI, Fig. 8 a, 10 c. 11 d. Disse 

 sekundære Septa ere forsynede med baade Længde- og 

 Tvermuskler, Tab. XI, Fig. 3 e. af hvilke dog de sidste 

 ere yderst lidet udviklede og vanskelige at iagttage, da de 

 beståa af kun enkelte Fibre. De longitudinelle derimod 

 ere stærkere og have et Leie, der er modsat det paa de 

 fuldstændige Septa; de ere nemlig placerede paa Skille- 

 væggens udventlige Flade og vende mod de interseptale 

 Rum. Paa disse listeformede. ufuldstændige Septa er 

 langs hele Kroppens indre Flade fæstet Acontier i større 

 og mindre Afstand, Tab. XI, Fig. 10 d, og længst ned 



apart from each other (Pl. XI, fig. 3. 11 fl). Of the 6 

 pairs of perfect septa. there are 2 pairs that distinguish 

 themselves somewliat from the others viz. directive septa, 

 which correspond to the oral angles or gonidia. The 

 septa stand, here, farther apart from each other. causing 

 the intraseptal space to be larger, (Pl. XI. fig. 3, 11 a) 

 and the muscular arrangement is different, as the trans- 

 versal muscles are placed on the inner surface. so that 

 they face towards each other and to a small extent fill 

 the intraseptal space (Pl. XI, fig. 3 a) ; whilst the longi- 

 tudinal muscles are seated upon the outer surtace of the 

 divisional wall and, consequently, face towards the adjacent 

 interseptal space (Pl. XI, fig. 3 b). Upon the remaining 

 4 pairs of septa (Pl. XI. fig. 3, 2) the muscular arrange- 

 ment is quite the reverse. The longitudinal muscles tire 

 seated on the inner surface of the divisional wall, and face 

 towards each other in the intraseptal space (Pl. XI, fig. 3 c), 

 whilst the transversal muscles occupy the outer surtace 

 (Pl. XI, fig. 3 d). At the origin ol the divisional walls 

 in the physa neither the longitudinal nor the transversal 

 muscles are strongly developed, but they become stronger, 

 progressively, as they extend farther up. 



The transversal muscles form a membrane, which is 

 extremely thin below, hut at the top, towards the cesop- 

 hagus, becomes thicker and foldet! and, as far as regards the 

 4 pairs of septa, fills about one halt of the interseptal 

 space. The longitudinal muscles are far stronger than the 

 transversal ones; up in the proximitv of the cesophagus, 

 they increase greatly in thickness and form a thick frutex 

 (Hag) which quite fills the intraseptal spaces (Pl. XI. rig. 

 3 c, 11 b). When one makes a transversal section of the 

 uppermost part of the animal, it appears as if the cesop- 

 hagus is enclosed by thick, whity-yellow pillars; these are 

 longitudinal muscles in somewhat contracted condition (Pl. 

 XI, fig. 10 b, 1 1 b). All the perfect septa carry mesen- 

 terial filaments, which are rather short. corkscrew shaped 

 when retracted, and stretch themselves only a little way 

 down the lowest part of the æsophagus, in the neighbour- 

 hood of which they originate. just at the mai-giu of the 

 longitudinal, muscular frutex (Pl. XI. fig. ln fl. 11 c). 



Between each 2 pairs of the perfect septa in the 

 interseptal space, there is a pair of secondary, imperfect 

 septa that also originate in the bottom of the physa (Pl. XI, 

 fig. 8 «, 10 c) and which are, here. scarcely half a millimetre 

 in breadth. but quickly become narrower as they proceed 

 upwards. where they appear as small, fillet-formed promin- 

 ences that pass quite up and on to the oral disc iPl. 

 XI, fig. 8 a, 10 c, 11 d). These secondary septa are fur- 

 nished with both longitudinal and transversal muscles 

 (Pl. XI. fig. 3 e), of which the last-named are, however, 

 extremely little developed and difficult to be observed, as 

 they consist of only a fe w fibres. The longitudinal muscles 

 are. upon the other haud, stronger. and are seated in a 

 reverse manner to those on the perfect septa; thus, they 

 are placed on the outer surface of the divisional wall, 

 and face towards the interseptal space. Upon these rillet- 

 formed, imperfect septa, along the inner surface of the 



