xvii NERVOUS AND REPRODUCTIVE SYSTEMS 489 



in their ordinary experience. To this end he passed over the 

 arm of a specimen a piece of indiarubber tubing, which clung 

 to it tightly. He found that the animal first tried walking off, 

 pressing the encumbered arm against the ground, so that the 

 piece of tubing was rubbed off. It was then replaced more 

 tightly than before ; the animal, having tried the first method 

 without result, waved the arm to and fro in the water till the 

 rubber floated off. In a third experiment the animal held the 

 rubber against the ground by a neighbouring arm, and drew the 

 encumbered arm out. When the rubber was replaced a fourth 

 time, the animal kicked it off by alternately pressing neighbour- 

 ing arms against it. Finally, when the rubber was put on so 

 firmly that all the above-mentioned methods failed, the arm was 

 broken off. Preyer concludes from this that Ophiuroids have a 

 high degree of intelligence ; but this may be doubted, and the 

 reader is referred to the account of Uexkull's experiments given 

 in the next chapter. There is, however, no doubt at all that 

 Ophiuroidea are by far the most active of all Echinoderms, and one 

 would naturally correlate this with higher psychic development. 



The radial nerve ends in a terminal tentacle sheltered by a 

 median plate at the end of the arm ; but eyes, such as are found 

 in Asteroids, are wanting, and the animal does not appear to be 

 sensitive to light. 



The reproductive system in Ophiuroids consists of a genital 

 stolon giving rise at its distal end to a genital rachis, which 

 extends in a circular course round the disc, ensheathed in an 

 "aboral sinus" (Fig. 213, ah) and swelling out so as to form 

 the gonads (testes or ovaries), where it passes over the inner 

 side of the genital bursae. The genital stolon (Fig. 213, gen.st) 

 is a compact ovoid organ, often termed on account of its shape the 

 " ovoid gland." It is situated close to the stone-canal, and, as in 

 Starfish, it indents the outer wall of the axial sinus ; but, unlike 

 the stolon of the Asteroid, it is separated from the general coelom 

 by a space, of which it forms the inner wall, but whose outer 

 wall is formed by a sheet of membrane. This cavity must be 

 carefully distinguished from the axial sinus of Asteroidea, to 

 which it was supposed at one time to correspond ; it is really 

 formed by a pocket-like ingrowth of the general coelom into the 

 septum dividing it from the axial sinus. The cells forming the 

 inner side of this pocket form the primitive germ-cells, which 



