108 DR. WILSON ON THE NERVOUS SYSTEM OF THE ASTERID^. 



vertebral spaces, most likely to be distributed to tbe vesicles of tlie feet and the peritoneal 

 covering of the ctecal chamber. 



The nerve-cord terminates at the distal end or point of the ray, in a bulbous swelling 

 coloured with different shades of red pigment and forming the eye-spots. From the • 

 ceUs lying immediately above the eye-bulb, filaments pass more or less obliquely down- 

 wards to the pigment-masses of the eye, termed cones by Haeckel. These eye-spots, as 

 Haeckel has pointed out, consist of pigment-cones, each containing a globular lens, and 

 having their bases directed towards the cornea. 



Though the nerve-cells do not apparently pass beyond the eye-spot, yet a great number 

 of their filaments extend further, to a curious contractile organ resembling, in many 

 points, one of the suckers, and, most probably, performing the function of a tactile organ. 

 The root of the eye-bulb rests upon the base of this tactile organ, and can thereby be 

 moved about tolerably freely. 



The nerve-cords, connecting the ganglia, are about half the thickness of the ambulacral 

 cords, these latter splitting into two pretty equal portions. They lie in close proximity to 

 the vascular perioral ring connected with the heart. Nerve-cells are found in them, though 

 it is difficult to detect the relation of these to the filaments. Some of these filaments 

 pass towards the mouth, while others are directed outwards. These nerve-cords are con- 

 sidered l)y MtiUer as simply the connective media, 1)y means of wliich the motions and 

 actions of the animal are harmonized. He supports this view by stating that those Star- 

 fishes which break themselves to pieces on being handled, may be prevented from doing 

 so if these cords are snipped through with a pair of scissors. 



The above is a general view of the nervous system of the Asteridse. We now proceed 

 to consider in detaO. the species examined. 



1. Solaster papposa. 



This species is the best-adapted for making a microscopic examination, because it pre- 

 sents the most simple structure. Unfortunately, however, it cannot be preserved long 

 alive in confinement, as it soon dyes the water with its pigment. 



The ambulacral cord is easily reached, lying in the wide ambulacral groove, and flanked 

 on either side by the single rows of comparatively thiclc suckers. The vertebrae forming 

 the groove for the nerve-cord and feet are few in proportion, widely separated, and but 

 loosely connected with one another. On a transverse section of the ray, they appear as 

 broad, irregular-shaped, calcareous plates, resting against one another along a certain 

 extent of their internal margins *. For convenience of description we may divide each 

 plate into a vertical portion extending from x to c, and an oblique from x to d. The ver- 

 tical portions are not equally in contact throughout their extent, but diverge above, owing 

 to the bevelling off of their margins. The triangular space thus formed is filled up by 

 fibrous tissue, which, for distinction, may be termed the superior ligament (c). The 

 oblique portions of the plates pass off laterally more or less widely from each other 

 according to the condition of the animal. Its ventral margin, or tliat turned towards 



* See Plate XIII. fia;. 1. 



