ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 527 



Nervous System of Ophiurids.* — Dr. C. F. Jickcli has extended 

 his observations on the nervous system of Echinoderms to Ophiurids. 

 If a number of sections of an arm be examined, four nervous systems 

 will be found extending in a longitudinal direction — there is the 

 ambulacral nerve of authors, which Dr. Jickeli proj)oses to speak of as 

 the ventral radial system ; placed on this, and separated from it by a 

 structureless lamella, is the paired ganglionic chain of Lange which it 

 is proposed to call the median radial system ; on the dorsal wall of the 

 perihfemal canal is a paired ganglionic chain, which may be distinguished 

 as the dorsal radial system. Two ganglionic chains lie between the 

 dorsal and ventral muscle on the external edge of the ambulacral plate ; 

 this is the lateral radial system. 



The ventral radial system gives off on either side a nerve which 

 passes up the wall of the perihsmal canal, and fuses with the neighbour- 

 ing cord of the dorsal radial system ; a branch on either side, which is 

 continued laterally, gives off a branch into the muscle between the 

 adambulacral and basal plate, and breaks up within the former into 

 several branches ; of these the innermost passes to the dorsal plate, 

 while the other branches enter an adambulacral papilla ; this may be 

 called the adambulacral nerve. Belonging also to the ventral radial 

 system is a nerve on either side for the ambulacral pedicels ; this forms 

 a subej^ithelial sheath around the whole pedicle, and becomes con- 

 solidated on its adoral side into a strong cord which is circular in trans- 

 verse section. 



The median radial system gives off a branch on either side which 

 innervates the ventral interambulacral muscle, and another which, 

 like it, arises from a ganglion, and innervates the dorsal interambu- 

 lacral muscle. The dorsal radial system gives off branches on either 

 side, one of which ends in a ganglion of the lateral radial system, 

 another which becomes connected with the nerve for the ventral inter- 

 vertebral muscle, and others which unite with the dorsal. The three 

 pairs of ganglia of the dorsal radial system are connected by transverse 

 commissures, but the author could not find the one described by 

 Lange. 



In all, each ambulacral segment has nine pairs of nerves ; in the 

 formation of the oral ring, the ventral, median, and dorsal radial systems 

 take part, and this therefore consists of three different rings. In 

 addition to these, another is formed by the lateral system ; as it lies 

 more externally than the others, it may be called the outer oral ring, 

 while the oral ring of previous authors is to be called the inner oral 

 ring. From this last the ventral ring gives off branches to each of the 

 two oral pedicels, and a strong branch, which, in its somewhat complex 

 course, gives off a number of branches ; all these are connected with the 

 corresponding branches of the adjoining rays. With them the bifurcate 

 branches of a third trunk become connected. The median and dorsal 

 rings combine to give a trunk which sends nerves to the adoral side of 

 the outer interradial muscle. Branches are given off dorsally from the 

 dorsal nerve-ring which appear to innervate the water-vascular ring 

 and the Polian vesicles. Strong nerves are given off at regular distances 

 to the " lips " ; these appear to be processes from all the three systems 

 which compose the inner oral ring. No indications were seen of the 



Zool. Anzeig., xii. (1889) pp. 213-8. 



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