88 



er et compliceret System af Hulrum, hvori Blodet 

 circiilerer. Mellein disse Skikter af Skallen er ogsaa 

 Skalkjertelen beliggende. Denne sidste viser sig 

 ved nærmere Undersogelse (se Tab. XV, Fig. 14) at 

 beståa af en flere Gange slyngeformigt bugtet Kanal, 

 der fertil delvis omgiver Insertionsareaen for Skal- 

 lens LnkkenTOskel, men hvis Hoveddel ligger umid- 

 delbart bag samme. Kanalens Udgangspnnkt synes 

 at ligge lige over den sidstnævnte Area og omtrent 

 paa samme Sted ogsaa dens Ende; men nogen skarp 

 Begrændsning mellera begge har jeg dog ikke kun- 

 net paavise, og det er muligt, at der her er en 

 direkte Kommunikation, saa at Kanalen i Virkelig- 

 heden danner et i sig selv tilbagegaaende Eor. Bag 

 !Muskelareaen danner Kanalen 3 ind i hverandre 

 liggende tungeformige Slynger, der, om man forføl- 

 ger Kanalen fra dens tilsyneladende Udgangspnnkt, 

 følger paa hinanden i en saadan Orden, at den mid- 

 terste Slynge er den forst dannede, den yderste den 

 2den, og den inderste den 3die. Den midterste og 

 yderste Slynge er forbundet ved en smalt iidlobende, 

 tungeformig Omboining, der strækker sig dorsalt 

 forover, og ender lige over Kanalens Udgangspnnkt. 

 Den yderste og inderste Slynge gaar over i hinan- 

 den ved en lignende, men bredere Ombøining, der 

 ligger mere ventralt, lige nedenunder Muskelareaen, 

 og her krydser den forreste Del af Kanalen. Over- 

 alt viser Kanalens Konturer sig iiregelmæssigt tak- 

 kede, og i dens Vægge sees spredte Cellekjerner, 

 givende den et glandulost Udseende. 



Det i Skallen indesluttede Dyr (se Tab. XV, 

 Fig. 1) indtager en forholdsvis liden Del af Skal- 

 caviteten, hvori det er frit suspenderet, kun fæstet 

 helt fortil ved det ovenomtalte dorsale Ligament 

 og ved Skallens Lukkemuskel. Saavel den foran 

 som bagenfor liggende Del af Legemet er derfor 

 frit bevægelig, og ilere Muskler sees ogsaa at pas- 

 sere fra det dorsale Ligament saavel fortil som 

 bagtil. Legemet lader sig naturligt dele i 2 Hoved- 

 afsnit, der med hinanden danner en storre eller min- 

 dre Vinkel, og hvis Begrændsning antydes ved det 

 dorsale Ligament og Lukkemuskelen. Det foran 

 disse Dele liggende Afsnit er meget mindre end det 

 bagenfor liggende og kan igjen deles i 2 under- 

 ordnede Afsnit, begrændsede fra hinanden oventil 

 ved en dyb Lidbugtniug. Den forreste Del er det 

 egentlige Hoved, den bager.'^te det saakaldte Nakke- 

 segment. Det bagenfor det dorsale Ligament og 

 Lukkemuskelen liggende, særdeles bevægelige Afsnit 

 lader sig ligeledes dele i 2, den egentlige Krop 

 (truncus) og Haledelen, hvoraf den forste er af meget 

 betydelig Størrelse, den anden ganske kort. 



Af ydre Vedhæng bærer Hovedet de 2 Par Folere 

 og fortsæ.tter sig bagtil paa Undersiden i Overlæben. 



there is a complicated .system of cavities in which 

 the blood circulates. Between these strata of the 

 shell, the .shell-gland is also situated. This last proves, 

 on a close examination (see PI. XV, fig. 14) to con- 

 sist of a twisted channel cnrled up in several windings, 

 which in front partially snrround the area of inser- 

 tion of the shell's adductor muscle, but of which 

 the greater number lie immediately behind it. The 

 point of issue of the channel appears to lie just 

 over the above-mentioned area, and its end also at 

 about the same place ; but I have not been able to 

 make out any sharp boundary between the two. 

 and it is possible that there is here a direct commu- 

 nication, so that the channel forms in reality a tube 

 running back into itself. Behind the muscular area, 

 the channel forms 3 linguiform coils lying within 

 one another, which, if the course of the channel be 

 traced from its apparent origin, so follow one an- 

 other, that the middle coil is the first formed, the 

 outermost one, the second, and the innermost, the 

 third. The middle and outermost coils are con- 

 nected by a narrowly projecting, lingiilar fold, 

 which extends forwards dorsally, and ends just 

 above the starting-point of the channel. The outer- 

 most and innermost coils run into one another with 

 a similar, but l)roader fold, which is more ventral 

 in position, just below the muscular area, and here 

 crosses the front part of the channel. The outline 

 of the channel is throughout irregularly jagged, 

 and scattered cell-nuclei are visible in its walls, _ 

 giving it a glandular appearance. I 



The enclosed animal (see PI. XV, fig. 1) occu- 

 pies a comparatively small portion of the caAdtj^ of 

 the shell, within which it is freely siispended, being 

 attached only at the very front by the before-men- 

 tioned dorsal ligament and by the adductor muscle 

 of the shell. Both the anteriorly and the posteri- 

 orly situated part of the liody can therefore lie 

 freely moved, and several muscles may be seen 

 passing from the dorsal ligament both backwards 

 and forwards. The body permits of being naturally 

 divided into two pi-incipal sections, which form 

 more or less of an angle with one another, and whose 

 limits are indicated by the dorsal ligament and the 

 adductor nmscle. The section situated in front of 

 these parts is much smaller than that lying behind, 

 and can be again divided into 2 sub-sections, sepa- 

 rated from one another above by a deep hollow. 

 The fore part is the head proper, the back part, the 

 so-called cervical segment. The extremely mobile 

 section situated behind the dorsal ligament and the 

 adductor muscle, is also capable of being divided 

 into two, — the body proper (trunk) and the caudal 

 part, the first of these being of very considerable 

 size, the second, quite short. 



Of the external appendages, the head carries 

 the 2 pairs of antennæ, and is continued backwards 



