97 



bagerste Strom. Begge modes ved det dorsale Liga- 

 ment, hvor de bøier om indad og udtommer sit Blod, 

 sammen med det fra Hovedet tilbagevendende, i den 

 forreste Del af Hjertet gjennem dettes Iste Par 

 Spaltaabninger. De ovrige 3 Far Spaltaabninger 

 synes at optage det Blod, der, efterat have circuleret 

 i Fodderne, vender tilbage til Hjertet. 



Respirationsapparat. — Rent morphologiskt maa 

 vistnok Foddernes Epipoditer ansees som de egent- 

 lige Eespirationsorganer, da de aabenbart svarer til 

 Gjellerne hos hoiere Krebsdyr. Men da ogsaa de 

 ovrige Dele af Fodderne viser en lignende over- 

 maade delikat Struktur, har man Grund til at an- 

 tage, at Resjiirationen ikke er udelukkende ind- 

 skrænket til hine Vedhæng, men foregaar overalt 

 paa Foddernes Overflade, hvad der ogsaa har givet 

 Anledning til den almindelig benyttede Benævnelse 

 Branchialfodder. Som det physiologiskt vigtigste 

 Eespirationsorgan maa vi dog utvivlsomt anse selve 

 Skallen, i hvilken der, som ovenfor anfort, huder 

 en meget livlig Blodcirculation Sted. Ved Foddernes 

 rhytmiske 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, sjnies alle 

 Betingelser at være tilstede for at en hurtig Gas- 

 udvexling her kan ske med det indenfor Membranen 

 strømmende Blod. 



Nervesystemet. — Den i Hovedet beliggende 

 Del af Nervesystemet er ikke vanskelig at obser- 

 vere paa tilstrækkelig gjennemsigtige Exemplarer. 

 Den bestaar af det saakaldte ovre Svælgganglion, 

 eller Hjernegaugliet, med de fra samme udgaaende 

 Nerver. Selve Hjernegaugliet 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. XVI, Fig. 9, 

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

 med hinanden i Midtlinien forbundne Halvdele, 

 hvoraf enhver er udtrukket i 2 divergerende, koni- 

 ske Fortsatser. Fra de forreste Fortsatser udgaar 

 de overordentlig lange og stærke Synsnerver og 

 desuden en ganske liden Nerve for Øiemusklerne. 

 Selve Synsnerverue passei'er fortil ind i Hovedets 

 Pandedel, hvor enhver af dem svulmer ud til et 

 kolleformigt Synsganglion. Begge Ganglier ligger 

 tæt sammen, uden dog at smelte sammen, og deres 

 Ender er kun ubetydeligt fjernet fra de sammen- 

 satte Øine (se Fig. 10). Fra dem udgaar talrige 

 fine Nervefibre, der trænger ind i Øinene og for- 

 binder sig med disses enkelte Synselementer. De 

 bagre Fortsatser af Hjernegaugliet (a') er noget 

 kortere end de forreste og mere udadrettede (se Fig. 

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



13 — G. 0. Sårs: Fauna Non'eoise. 



anterior stream, and one considerably longer pos- 

 terior one. They meet at the dorsal ligament, where 

 they turn inwards, and empty their blood, together 

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

 terior part of the heart through that organ's iirst 

 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 morpho- 

 logical point of view, the epipodites of the legs 

 must be considered as the true respiratory organs, 

 as they evidently answer to the gills in higher 

 Crustaceans. But as the other parts of the legs 

 also show a similar exceedingly delicate structure) 

 there is reason to suppose that the function of 

 respiration is not contined exclusively 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 physiologically most important organ of respi- 

 ration however, we must undoubtedly regard the 

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

 circulation of the blood goes on. By the rhythmical 

 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 delicate 

 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 transparent specimens. It consists 

 of the so-called supra-æsophageal ganglion or cere- 

 bral ganglion, with the nerves proceeding from it. 

 The cerebral gangli(ui itself is of no very consider- 

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

 far back in the head, immediately behind the ocel- 

 lus, with which it is connected by a tolerably 

 broad projection (see also PI. XVI, figs. 9, 10). It 

 consists as usual of 2 symmetrical halves connected 

 with one another in the median line, each half 

 being drawn out into 2 divergent conical protuber- 

 ances. From the foremost of these issiie the excee- 

 dingly long and strong optic nerves, as also a very 

 small nerve for the ocular muscles. The optic 

 nerves themselves pass forwards into the frontal 

 part of the head, where they each swell out into a 

 club-like optic ganglion. These ganglia lie close 

 together without however coalescing, and their 

 extremities are at only a slight distance from the 

 compound eyes (see fig. 10). Numerous delicate 

 nerve-fibres issue from them, entering the e3'es, and 

 connecting themselves with the several visual ele- 

 ments of those organs. The hind protuberances of 

 the cerebral ganglion (a') are rather shorter than 

 the front ones, and directed more outwards (see 



