j Echino derma. 



the radial schizocoel spaces, and also, through the axial sinus, with the aborai 

 schizocoel ring. The radial blood-lacuna occupies the mid-dorsal line of the nerve 

 band, and is attached by delicate threads to the wall of the schizocoel space around 

 it. Its wall consists of a thin membrane bearing oval nuclei, and its lateral branches 

 end in the lacunae of the connective tissue layer in the tube-feet. The oral blood- 

 ring uniting the radial channels is connected with lacunae in the proximal end of 

 the axial organ. The aborai blood-lacunar ring and its relations to the genital 

 cord were noticed in the Bericht for 1887 Ech. p 3, 8. Its extensions over the 

 genital glands become reduced to a system of lacunae in a thin layer of connective 

 tissue. Some of the germ cells develope into ova, and others around them into 

 follicle cells, while those of the testis give rise to spermatoblasts. - - The ciliated 

 cells in the wall of the gut each bear a number of small rods, on which the cilia 

 are not very close. Beneath the cells are nerve fibrils which are especially abun- 

 dant near the beginning of the gut. The muscle fibres of the arms show a double 

 oblique striation, especially in the contracted state, but those of the body wall 

 are faintly striated lengthways. 



Jickeli describes the radial nervous system of Ophiurids as consisting of 

 four parts, which he calls respectively, ventral, median, dorsal, and lateral. The 

 ventral system, or ambulacral nerve, gives off three pairs of branches: --one 

 ascends in the wall of the perihaemal canal and joins the dorsal system ; another 

 enters the adambulacral plate and breaks up into branches which supply the spines ; 

 the third, the pedal nerve, forms a subepithelial sheath round the whole foot, 

 together with an annular cord near its base. The median system is the ganglionic 

 cord of Lange, and two branches leave each ganglion which supply the dorsal 

 and ventral intervertebral muscles. The dorsal system is a double ganglionic 

 cord lying in the dorsal wall of the perihaemal canal. It gives off branches to 

 the two intervertebral muscles which join those of the median system, and a third 

 branch which enters a ganglion of the lateral system. The three pairs of ganglia 

 from which these branches arise are united by transverse commissures. The 

 lateral system consists of a ganglionic cord on either side of the ambulacral 

 plate. It is connected with both dorsal and ventral systems, and branches of it 

 pass down along the lower wall of the inferior perihaemal space, to supply the 

 ventral integument. To each ambulacral segment there thus belong 9 pairs of 

 nerves; but in the disk the arrangement is somewhat modified. A large trunk, 

 formed by the union of fibres from the 3 d , 4 th , and 5 th adambulacral nerves, 

 supplies the musculature of the genital scales and radial shields, and communicates 

 with its fellow of the next radius. The oral nerve ring consists of three parts, 

 derived respectively from the ventral, median, and dorsal systems. The median 

 is divided into a double ganglionic cord by the blood- vascular ring, and, like 

 the dorsal one, sends branches to the outer interradial muscles. The nerves of 

 the water-vascular ring and Polian vesicles also arise from the dorsal ring ; while 

 the ventral one supplies the buccal feet and the inner interradial muscles. All 

 three systems send strong branches into the lip, but there is no subepithelial 

 plexus in the gut. Ludwig's bursalnerveis part of an outer nerve ring formed 

 by the union of branches from the lateral systems of the third ambulacral 

 segments. 



Ives notices the wide range of variation in the external characters of Ophiura 

 panamensis and 0. teres. The darker varieties of the former species occur at the 

 more northerly localities. 



Semon ( 2 ) describes an abnormal individual of Ophiopsila aranea which has 

 ihree small arms and two larger ones, both partially regenerated and forming a near- 

 ly continous line instead of the normal angle of 141. He believes them to be really 



