20 



Hos Bathycrinus Carpenteri gjenfinde vi disse 3 Sy- 

 stemer vel udviklede. 



Omkring det femkamrede Organ er det dorsale Nerve- 

 systems Centralorgan leiret og omslutter det tæt som en 

 Kappe. At det virkelig er Nervemasse, det her gjælder. 

 frémgaar tydeligt nok af Strukturen, der bestaar af Nerve- 

 fibriller med indblandede Nerveceller. Fra denne Nerve- 

 masses dorsale Del udgaar en tyk Stamme, som følger og 

 omgiver det femkamrede Organs Forlængelser i Stilken, 

 Tab. III, Fig. 9 e, 10 c, og hvor disse ophører, ser man 

 Nervemassen fortsætte sit Løb, omgivende Centralkarret, 

 til ned imod Roden. Centralkarret er ligesom indkapslet 

 af Nervemasse, hvorfra sees hist og her enkelte Orene ud- 

 gaa til de nærmest omgivende Dele. Imod den ventrale 

 Del antage Nervefibrillerne en mere koncentrisk, næsten 

 ringforrnig Retning, og herfra udspringe 5 temmelig tykke 

 Stammer, hvorved en tydelig femkantet Ring dannes. Tab. 

 IV, Fig. 9 a. Disse 5 Stammer, Tab. IV, Fig. 9 b, der 

 tåge sin Begyndelse i den øverste Del af Iste Radiale, til- 

 tage nu i Tykkelse som Radialnerve, efterhaanden som de 

 stige op i 2det og 3die Radiale. Men førend de gaa over 

 i 2det Radiale afgive de en Tvergren. der som en Kommissur 

 gaar fra den ene Oren til den anden, hvorved en udpræget 

 femkantet Ring dannes. Kommen op til øverste Trediedel 

 af 3die Radiale, deler hver Stamme sig i to store Orene, 

 som gaa til liver sin Arm og er den egentlige dorsale 

 Brachialnerve. Hamann angiver, at de :"i Stammer, der 

 udgaa fra < Vntralmassen hos Antedon rosacea, strax dele 

 sig dichotomisk for atter igjen at forene sig til en tyk 

 Stamme (Radialnerven). Denne Deling har det ikke vant 

 mig muiigt at iagttage, omenskjønt jeg er tilbøielig til 

 at tro, at den ogsaa finder Sted hos Bathycrinus Carpenteri. 

 Efterat Radialnerven har delt sig i 2 Orene, men førend 

 disse forlade odie Radiale, foregaar der imellem dem en 

 yderst mærkelig Anastomosering, som først udførlig er be- 

 skreven af Professor Ludvig under Navnet Chiasma nervo- 

 rum brachialium, idet der fra den ene Arm gaar en tynd 

 Gren, som krydser en lignende fra den modsvarende Arm 

 og hvorved Chiasmaet dannes. Strax ovenfor Ohiasmaet 

 sees en temmelig tyk Kommissur der forener begge Armgre- 

 nene 1 . Foruden denne Kommissur. skal der ifølge Perrier 2 

 endnu være en, som er kortere og tykkere, end den ovenfor 

 beskrevne, hvilken baade Ludvig og Hamann skal have 

 overseet. Det er ikke lykkes mig at finde denne Kommis- 

 sur, medens Krydsningen (Chiasmaet) ikke var saa særdeles 

 vanskeligt at iagttage hos Bathycrinus Carpenteri. 



Hver Armgren forlader nu det 3die Radiale og gaar 

 ind i Armen, hvor den følger Dorsalfladen over Dorsalka- 



Otto Hamann, Beitrage zur Histologie der Echinodermen. Heft 

 4. Anatomie und Histologie der OpMuren und Crinoiden, Pag. 

 65. Jena 1889. 



Nouvelles Arohives du Museum. T. IX. pag. 107. Tab. 18, Fig. 

 147, ch, en. 



In Bathycrinus Carpenteri we again recognise these 

 3 systems well developed. 



The central organ of the dorsal nervous system is 

 found entrenched round the five-chambered organ, enclosing 

 it closely like a cloak. That it is really nervous substance 

 we have here to do with, appears distinctly enough from 

 the structure, which consists of nerve-fibres with nerve-cells 

 mixed up with them. From the dorsal portion of this 

 nervous mass there issues a thick stem. which follows and 

 encloses the five-chambered orgaiVs prolongations in the 

 stalk (Pl. III, fig. 9 e, 10 c), and where these cease we ob- 

 serve the nervous mass continuing its eourse. surrounding 

 the central vessel, to down near the root. The central 

 vessel is, as it were, encapsuled by the nervous mass, from 

 which a few branches are seen to jssue here aud there to 

 the nearest surrounding parts. Towards the ventral part 

 the nerve-fibrils assume a more concentric. almost annular 

 direction, and from here 5 pretty thick stems issue. thereby 

 producing a distinct five-sided ring (Pl. IV. fig. 9 a). These 

 ."> stems (Pl. IV, fig. 9 b), which originate in the uppermost 

 part of the Ist radial, increase now in thickness, as radial 

 nerves, as they gradually ascend in the 2nd and 3rd radials. 

 But before they pass over to the 2nd radial they give off 

 a transversal branch which. like a commissure, passes from 

 the one branch to the other, whereby a distinct five-sided 

 ring is formed. Arrived at the uppermost third-part 

 of the 3rd radial, each stem divides itself into two large 

 branches, each of which passes to an arm and forms the real 

 dorsal brachial nerve. Hamann states that the 5 stems 

 which issue from the central mass in Antedon rosacea, 

 immediately divide themselves dichotomically. becoming again 

 united into a thick stem (the radial nerve). It has not 

 lieen possible, for me, to discover this division, although I 

 am disposed to believe that it also occurs in Bathycrinus 

 Carpenteri. After the radial nerve has divided itself into 

 2 branches, but before these abandon the ord radial, there 

 takes place between them an extremely remarkable anas- 

 tomosis, which has first been fully described by Professor 

 Ludvig under the designation chiasma nervorum brachialum, 

 as there passes from the one arm a thin branch which 

 crosses a similar one from the corresponding opposite arm, 

 thereby producing the chiasma. Immediately above the 

 chiasma a pretty thick commissure is observed, which unites 

 both the branches of the arm. ' Besides this commissure 

 there is, according to Perler -', vet another one, which is 

 shorter and thicker than the one deseribed, and which both 

 Ludvig aud Hamann have omitted to observe. I have not 

 been fortunate enough to discover that commissure, while it 

 was not particularly difficult to observe the inter-crossing 

 i the chiasma) in Bathycrinus Carpenteri. 



Each brachial branch now leaves the 3rd radial and 

 passes into the arm, where it' follows the dorsal surface 



1 Otto Hamann, Beitrage zur Histologie der Echinodermen. Heft 

 4. Anatomie und Histologie iler Ophiuren und Crinoiden, Pag. 

 (35. Jena 1889. 



2 Nouvelles Archives du Museum. T. IX. pag 197. Pl. 18, fig. 

 147, ch, en. 



