96 



dele som liver udnmiuler med en kort Udforselsgang 

 noget lateralt i Tarmens forreste Del, og i sin Peri- 

 pheri er delt i talrige bugtede Blindsække, ialminde- 

 lighed fyldte med et intenst gultfarvet Stof. Hvert 

 Organ udsender nedad en Sidegren, der i Hovedets 

 ventrale Del, umiddelbart foran Basis af Overlæben, 

 oploser sig i flere uregelmæssige Lappe. Hoved- 

 massen af Organet ligger dog dorsalt, hvor det 

 sammen med det tilsvarende Organ paa den anden 

 Side danner en tilsyneladende sammenliængende 

 Kalot over Tarmens forreste Del (se Fig. 2 og 3). 



Circulationsapparatet. 



Hjertet (se Tal). XV, 



Fig. 1) er beliggende ovenover Tarmen i den forre- 

 ste Del af Truncus, strækkende sig fortil ind i 

 Nakkesegmentet, bagtil ind i det 4de fodbærende 

 Segment. Det har Formen af et fortil noget videre 

 cylindriskt Ror, aabent i begge Ender, og desnden 

 forsynet til hver Side med 4 tydelige Spaltaabninger, 



1 Par for Nakkesegmentet, de 3 ovrige Par for de 

 3 forreste Segmenter af Tranens. Af nogen virke- 

 lige Blodkar har jeg ikke kunnet finde noget Spor; 

 men Blodet folger dog nnder sin Circnlation i Lege- 

 met visse meget bestemte Baner. Da Blodlegemerne 

 er meget tydelige, er det ikke saa vanskeligt paa 

 tilstrækkelig gjennemsigtige levende Exemplarer at 

 studere de væsentligste Træk af Circnlationen, og 

 jeg .skal i det folgende i Korthed beskrive samme, 

 saaledes som jeg har troet at finde den ved gjen- 

 tagne omhyggelige Undersogelser. Fra den bagre 

 Del af Legemet kommer en stærk Strom af Blod, 

 der folger Rygsiden af Truncns og passerer direkte 

 ind i Hjertet gjennem dettes bagre Aabning. Ved 

 Hjei'tets Systole lukkes denne Aabning, saavelsom 

 de laterale Spaltaabninger, og Blodet stedes med 

 stor Kraft ud af Hjertets forreste Ende. En Del 

 af den saaledes af Hjertet udkomne Blodmasse pas- 

 serer direkte ind i den forreste Del af Legemet og 

 forsyner Hovedet med dets forskjellige Vedhæng 

 med Blod. En anden Blodstrom boier pludselig om 

 under Hjertet og løber bagover, umiddelbart neden- 

 for den tilforende dorsale Blodstrom, liga til Hale- 

 delen, hvor den synes at boie om paa Bugsiden af 

 Dyret for at forsyne Branchialfodderne med Blod. 

 En 3die betj^delig Del af den fra Hjertet udstodte 

 Blodmasse passerer til hver Side mod Skallens Lukke- 

 muskel, hvor den i Umkredsen af Muskelareaen 

 trænger ind i selve Skallen. Herfra fordeles Blodet 

 rundt om i de to Val vier, idet det i forskjellige Baner 

 gjennemstrommer det complicerede System af Hul- 

 rum, der, som ovenfor anfort, findes niellem disses 



2 Lameller. Efrerat have circuleret i Skallen sam- 

 ler Blodet sig lidt efter lidt i 2 dorsale Hoved- 

 stromrae, der lober langs Rygkanten af Skallen, 

 en ganske kort forreste, og en Iietvdelig lænirere 



is there also situated in the head. As in Lepirlurus. 

 this organ eonsists of two symmetrical halves each 

 opening by a short excretory duct somewhat later- 

 ally in the anterior part of the intestine, and 

 divided in its periphery into numerous cæca, gene- 

 rally filled with a substance of an intense yellow 

 colour. Each oi'gan sends down a lateral branch 

 which is resolved into several irregular lobes in the 

 ventral part of the head immediately in front of the 

 base of the labrum. The gi'eat Imlk of the organ, 

 however, is situated dorsally, where, together with 

 the corresponding organ on the other side, it forms 

 an apparently continuous cap over the anterior part 

 of the intestine (see figs. 2 and 3). 



Circulatory System. — The heart (see PL XV, 

 fig. 1) is situated al)ove the intestine in the anterior 

 part of the trunk, extending forwards into the cer- 

 vical segment, and backwards into the 4th pediger- 

 ous segment. It has the sha|ie of a cylindiical 

 tube, rather wider in front, and open at both ends, 

 and also furnished at each side with 4 distinct ostia, 

 one pair for the cervical segment, the other 3 for 

 the 3 foremost segments of tlie trunk. I have been 

 unal>le to find any trace of actual blood-vessels, but 

 during its circulation through the body, the blood 

 follows certain fixed courses. As the corpuscles are 

 very distinct, it is not difficult in sufficiently tran- 

 sparent living specimens to study tJie princijial fea- 

 tures of the circulation, and I will here briefly 

 describe them as I have found them by repeated 

 careful investigations to be. From the hind ])art of 

 the body comes a strong stream of blood, keeping 

 to the dorsal side of the trunk, and passing directly 

 into the heart through its posterior aperture. This 

 aperture, as well as tlie lateral ostia, is closed by 

 the heart's systole, and the blood is ejected with 

 great force from the anterior end of the heart. A 

 portion of the c^uantity of blood thus issuing from 

 the heart, passes directly into the anterior part of 

 the body, and supplies the head and its varioiis 

 appendages with blood. Another stream of blood 

 turns suddenly below the heart and flows back- 

 wards immediately below the afferent dorsal stream 

 right up to the caudal ]iart, where it appears to 

 turn to the ventral side of the animal, in order to 

 supply the branchial legs with l)lood. A third con- 

 siderable part of the i|uantity of blood ejected from 

 the heart, passes on both sides towards the adductor 

 muscle of the shell, where, witliin the circumference 

 of the muscular area, it forces its way into the 

 shell itself. From tliis the blood is distributed over 

 the two valves, flowing by varions courses througli 

 the complicated system of cavities wliicli. as stated 

 above, is found between their 2 laniellæ. After 

 having circulated in the shell, the blood gradually 

 collects in two principal, dorsal streams which run 

 along the dorsal edge of the shell, one i[uite short 



