50 



tiske Bevægelser, der med stor Eegelmæssiglied for- 

 plantes langs ad dens hele Længde, ialmindelighed 

 i Eetningen bagfra fortil. 



Circulationssystemet. — Hjertet danner (se Tab. 

 VI, Fig. 2, o, lic) et overordentlig langstrakt, med 

 bestemte Mellenirnm indsnoret Ror, der strækker sig 

 ovenfor Tarmen fra Nakkesegmentet og bagtil lige 

 ind i Halens næstsidste Segment. Det er ved fine 

 Miiskeltraade fæstet til Indsiden af Ryggens Inte- 

 o-nment, off viser for hvert Segment et Par venose 

 Spaltaabninger, hvorigjennem Blodet optages i Hjei^- 

 tet. Den samlede Blodmasse, som paa denne Maade 

 treenger ind i Hjertet, udstødes dels fra den forreste, 

 dels fra den Ijageste Ende, og kommer derpaa ind i 

 væglose Hiilrnm mellem de foiskjellige (Jrganer. 

 Skjondt saaledes et egentligt Kars3'steni, bestaaende 

 af Arterier og Vener, ganske mangler, circnlerer dog 

 Blodet med stor Regelmæs.sighed omkring i Lege- 

 met, idet det folger visse bestemte Baner. Blodet 

 er, som sædvanligt, farvelost og indeholder en 

 Mængde smaa, tildels amoboide Blodlegemer, hvis 

 Gang let lader sig forfolge hos det levende Dyr 

 linder Mikroskopet. Hjertets Piilsationer, hvornnder 

 Spaltaabningerne afvexlende aabnes og hikkes, er 

 særdeles livlige, saa det er meget vanskeligt at 

 tælle, hvormange der sker i Minuttet. 



Nervesystemet. — ("entraldelene af Nervesyste- 

 met bestaar, som hos andre Crustaceer, af et dorsalt 

 Parti, det øvre Svælgganglion eller Hjernegangliet, 

 og af en ventral Del, den saakaldte Bngganglie- 

 kjæde, begge forbundne ved en omkring Spiser(n'et 

 lobende Conimissur (se Tab. VIII, Fig. 1). 



Hjernegangliet (se Fig. 1, 4. 17), der har sin 

 Plads i den forreste Del af Hovedet, lige foran Be- 

 gyndelsen af Tarmen, er af temmelig betydelig Stør- 

 relse, og bestaar af 2, i Midten med hinanden for- 

 bundne symelriske Halvdele. Oventil danner det 

 flere Lappe, der delvis omfatter Basis af det enkle 

 Øie (se Fig. 4), og til hver Side fortsætter det sig 

 i den mægtigt udviklede Synsnerve (o), efterat have 

 udsendt en tynd Nerve til Iste Par Antenner la'). 

 Et andet Par Nerver sees at udgaa fra Hjernegang- 

 liet hengere fortil, til hver Side af det enkle <Me. 

 De ender hver med en liden ganglios Opsvulmning 

 umiddellmrt under en liden grubeformig Fordybning 

 i Hovedi'ts forreste Integument (a), rimeligvis sva- 

 rende til (h' omtrent paa samme Sted hos Lininetis 

 ibrekommende eilierede (Jrulier, der ialmindelighed 

 ansees for et Slags Sandseorga-n. Ner\-erne for 2det 

 Par Folere (a**), der hos Hannei'nc er betydelig 

 stan'kere end hos Hunnerne, uds]u-inger fra den for- 

 reste Del af Svælgcommissurerne. Disse sidste for- 

 bindes, ind(!n de omfatter Spiserøret, ved en tynd 

 Tværcommissur (se Fig. 1 og 4), der ligger ved P>asis 

 af Overheben. 



be observed, these being transmitted with great 

 regularity throughout its entire length, generally 

 from behind forwards. 



Circulatory system. — The heart (see PL VI, 

 tigs. 2, 3, lie) consi.sts of an exceedingly elongated 

 tube, constricted at I'egular intervals, and extending 

 above the intestine from the cervical segment back- 

 wards into the penultimate segment of the tail. It 

 is attached by fine muscle-fibres to the inside of the 

 dorsal integument, and exhibits, in each segment, 

 a pair of venous ostia, thi-ough which the blood 

 is received into the heart. The accumulated mass 

 of blood, which thus forces itself into the heart, is 

 ex])elled partly trom the anterior, partly from the 

 posterior end, and then enters the several cavities 

 between the various organs. Although there is thus 

 a total absence of a true vascular system (H)nsisting 

 of arteries and veins, yet the blood circulates with 

 great regularity through the body, following certain 

 fixed courses. The blood is, as usual, colourless, 

 and contains a number of small, partly am(jel)ous 

 blood-corpuscles, whose course may be easilj' traced 

 under the microscope. The pulsations of the heart, 

 during which the o.stia alternately open and close, 

 are exceedingly rajnd, so that it is very difficult to 

 count the iiumlier occurring in a minute. 



Nervous system. — The central portion of the 

 nervous system consists, as in other (.'rustaceans, 

 of a dorsal part, the supraæsophageal or cerebral 

 ganglion, and of a ventral part, the so called ventral 

 ganglion chain, connected with one another by a 

 commissure round the æsophagus (see PI. VIII, fig. 1). 



The cerebral ganglion (see figs. 1, 4 and 17), 

 which is situated in the anterior part of the head, 

 just in front of the commencement of the intestine, 

 is of considerable size, and consists of 2 symmetri- 

 cal halves connected with one another in the middle. 

 Above, it forms several lobes which partially sur- 

 round the base of the ocellus (see fig. 4), and, after 

 sending out a fine nerve to each of the first pair of 

 antennæ (a'), continues on each side in the form of 

 the ])Owerfully developed optic nerve (oV A second 

 pair i>f nerves are seen to issue from the cerebral 

 ganglion farther forward, on each side of the ocellus. 

 They each end in a little ganglionic protuberance 

 immediatel\- below a small pit-like depression in the 

 anterior integument of the head ^a) ]irobal)ly an- 

 swering to the ciliated pits occurring in ahout the 

 same place in Liimifitix, and whicli are generally 

 considered to l)e a kind of organ of sense, 'ilii' 

 nerves for the second [lair of antennæ (a ''^) whicli 

 are considerably stronger in the males than in the 

 females, originate from tlie anterior part of the 

 (esophageal commissures. These, before they encircle 

 the æsojdiagus, are connected by a thin transverse 

 commissure (see figs. 1 and 4) lying near the base 

 of the anterior lip. 



