97 



ha£:erste Strom. Begtre moiles ved det dorsale I ji o-a- 

 ment, livoi' de Loier om iiidad o'^ udtommer sit Klod, 

 sammen med det fra Hovedet till)a,f!;eveii(lende, i den 

 forreste Del af Hjertet gjennem dettes Iste Par 

 Spaltaabninger. De ovrige 3 Far Spaltaalminger 

 synes at optage det Blod, der, efterat have cireuleret 

 i Fodderne, vender tilbage til Hjertet. 



Respirationsapparat. — Fent morphologiskt maa 

 vistniik {""oildernes l']j)i]Hiditer ansees som de egent- 

 lige Respirationsorganer, da de aabenbart svarer til 

 Gjellerne lios lioiere Krebsdyi'. ]\Ien da ogsaa de 

 ovrige Dele af Fodderne viser en lignende (jver- 

 maade delikat Stniktur, har man (irnnd til at an- 

 tage, at Fes])irationen ikke er ndelukkende ind- 

 skrænket til hine Vedhæng, men foregaar overalt 

 paa Foddernes Overflade, livad der ogsaa har givet 

 Anledning til den almindelig benyttede Renævnelse 

 Branchialfodder. Som det physiologiskt vigtigste 

 Re.spirationsorgan maa vi dog utvivlsomt anse selve 

 Skallen, i hvilken der, som ovenfor anfort, finder 

 en meget livlig Blodeirculation Sted. Ved Foddernes 

 rlu'tmiske Bevægelser sker der nemlig en stadig For- 

 nyelse af Våndet indenfor Skallen, og da dette Vand 

 umiddelbart beskyller den særdeles delikate Mem- 

 bran, der beklæder Valvlerne indvendigt, synes alle 

 Betingelser at være tilstede for at en hurtig Gas- 

 udvexling her kan ske med det indenfoi' JVIeml)ranen 

 stronnnende Blod. 



Nervesystemet. — Den i Hovedet beliggende 

 Del a f Xi'rvp.s\-stemet er ikke vanskelig at obser- 

 vere paa tilstrækkelig gjennemsigtige Exeniplarer. 

 Den bestaar af det saakaldte ovre Svælgganglion, 

 eller Hjernegangliet, med de fra samme udgaaende 

 Nerver. Selve Hjernegangliet er ikke af særdeles 

 betydelig Størrelse, og ligger (se Tab. XV, Fig. 2) 

 temmelig langt tilbage i Hovedet, umiddelbart bag 

 det enkle Øie, hvormed det forbinder sig med en 

 temmelig bred Fortsats (se ogsaa Tab. X\'l, Fig. lb 

 10). Det bestaar, som sædvanlig, af 2 symetriske, 

 med hinanden i j\Iidtlinien forbundne Halvdele, 

 hvoraf enhver er udtrukket i 2 divergca'ende, koni- 

 ske Fortsatser. Fra de forreste Fortsatser udgaar 

 de overordentlig lange og stærke Synsnerver og 

 desuden en ganske liden Nerve for Øieniusklerne. 

 Selve Synsnervei'ue passerer tbrtil iiid i liovedets 

 1'andedel, h\(ir enhver af dem s\ulinrr ud til et 

 koUeformigt Synsganglion. Ilegge (ianglier ligger 

 tæt sammen, uden dog at smelte sammen, og deres 

 Ender er kun ubetydeligt fjernet fra de sammen- 



satte Øine (se Fig. 10). h'ra 



udgaar talrifre 



tine Nervetibre, der trænger ind i Øinene fig tbr- 

 binder sig med disses enk(dte Synselementer. De 

 bagre Fortsatser af Hjernegangliet (a') er noget 

 kortere end do tbrreste og mere udadrettede (se Fig. 

 10), men af en lignende konisk Form. De giver 



!.'{ — G. 0. Sårs; Fainia -VonrflKr. 



anterior stream, and (ine considerably longer pos- 

 terior one. They meet at the dorsal ligament, where 

 they turn inwards, and em])ty their blood, together 

 with that running back from the iiead, into the an- 

 terior part of the lieart through that organ's tirst 

 pair of ostia. The 3 other pairs of ostia appear to 

 receive the blood which, after having circulated in 

 the legs, returns to the heart. 



Respiratory Organs. — From a purely miir])ho- 

 logical point nf \'icw, the epijiodites of the legs 

 must be considered as the true res])iratory organs, 

 as they eA'idently answer to the gills in iiigher 

 Crustaceans. But as the other parts of the legs 

 also .show a similar exceedingly delicate strueturei 

 there is reason to su]i]iose that the function of 

 respiration is not contined excdiisively to these 

 appendages, but is carried on over the entire sur- 

 face of the leg, a circumstance which has given rise 

 to the generally used term — branchial legs As 

 the pln'siologically most important organ of respi- 

 ration iiowever, we must undoubtedly regard the 

 shell itself, in which, as stated above, a very active 

 circulation of the Itlood goes on. By the rhytlimical 

 movements of the feet, a constant renewal of the 

 water inside the shell takes place, and as this water 

 is in immediate contact with the peculiarly didicate 

 membrane lining the interior of the valves, all the 

 conditions requisite for a rapid exchange of gas 

 with the blood flowing within the membrane, appear 

 to be present. 



Nervous System. — That part of the nervous 

 system lying in the head is not difficult to observe 

 in sufficiently transjiarent specimens. It consists 

 of the so-called sujira-n'sophageal ganglion or cere- 

 bral ganglion, with the nerves ju'oceeding from it. 

 The cerebral ganglion itself is of no very consider- 

 able size, and is situated (see PI. XV, fig. 2) rather 

 far back in the liead, immediately behind the ocel- 

 lus, with which it is connected by a tolerably 

 broad projection (see also PI. XVI, figs, i), 10). It 

 consists as usual of 2 symmetrical iialves connected 

 with one another in the meilian line, each half 

 being drawn out into 2 divergent conical protuber- 

 ances. From the foremost of tliese issue the excee- 

 dingly long and strong ojitic nerves, as also a very 

 small nerve for the ocular muscles. The optic 

 nerves themselves ])ass forwards into the frontal 

 ])art of the head, where they each swell out into a 

 (dub-like optic ganglion. Tiiese ganglia lie (dose 

 together without Iiowever coalescing, and their 

 extremities arc at only a slight distance from the 

 compound eyes (see fig. 10). X^umerous delicate 

 nerve-fibres issue from them, entering the eyes, and 

 connecting themselves witli the several visual ele- 

 ments of those organs. Tlic liind protuberances of 

 the cerebral ganglion (a') arc rather shorter than 

 the front ones, and directed more outwards (see 



