760 SUMMARY OF CUERENT RESEARCHES RELATING TO 



however, brought out by these experiments. The animals were often seen 

 to be in doubt as to which ray should go first ; Asterids often turned on 

 their axis before moving forwards, and the direction of the turning might 

 be with or against the hands of a watch. There was a remarkable varia- 

 tion in the length of the latent period, one and the same individual giving 

 a few seconds or an hour ; in general the very long latent periods were 

 observed after several experiments had been performed on the same indi- 

 vidual. After amputation of one or more rays the latent period was 

 increased. 



Observations were made on the dependence of movements on sensory 

 impressions ; with regard to the influence of light, the results of Romanes 

 are confirmed, and it was noticed that very slight difierences in the illumina- 

 tion of the walls was sufficient to cause a movement of most Asterids (never 

 of Ophiurids) from the less to the more brightly illuminated part. Experi- 

 ments to test the sense of colour were all negative in their results ; the 

 photochemical sensitiveness of the skin was repeatedly observed, and it 

 was found that there were colouring matters present which are sensitive to 

 light ; Asterids certainly seem to have specific nerves sensitive to luminous 

 impressions and connected organically with the co-ordination centres. 



The great sensitiveness of all star-fishes to alterations in the concentra- 

 tion and chemical composition of sea water shows a great power of dis- 

 tinguishing sensations, but the fact that any part possesses this chemical 

 sensitiveness speaks against the supposition that there is any specific sense 

 of taste. Experiments made along the lines of those used by Romanes on 

 the sense of smell did not give constant results, but it is possible that the 

 animals which failed to be attracted by the food were not hungry ; the 

 interesting and even entertaining recital of experiments shows that very 

 complicated movements are made, and that, at least in a state of inanition, 

 there is a great irritability of the specific olfactory nerves, and a close 

 connection between these and the co-ordinating centres; certain olfactory 

 impressions cause a rapid and direct movement of the whole animal to the 

 place whence they came. 



The experiments that have been recorded have, incidentally, given con- 

 siderable evidence as to the presence and extent of the tactile sense. 



Summing up the results of his important investigations. Prof. Preyer 

 commences by calling attention to the proof that Asterids, Ophiurids, and 

 Crinoids perform quite a series of movements, which cannot be of a purely 

 reflex nature, but presuppose a certain intelligence ; it has further been 

 shown that the central or peripheral portions of the nervous system are 

 functionally unequal in value ; by means of the " ambulacral law " it is 

 possible to say beforehand how a given star-fish will respond to various 

 stimulations of its pedicels, and when stimulation will irradiate and when 

 it will not. Others of the experiments add to our knowledge of the com- 

 parative value of poisons. A large series of observations have been made 

 on the physical and psychical functions. 



In the reflex retraction of the suckers we find coming into play the 

 sensory nerve-fibres passing from the pedicels into the sensory ganglion- 

 cells of the radial medulla, connecting fibres between these and the neigh- 

 bouring motor ganglion cells, the motor fibres from the latter into the 

 muscular fibres of the pedicels, sensory nerve-fibres from the dorsal integu- 

 ment into the sensory ganglion cells of the radial medulla, and, lastly, 

 connecting fibres between the latter and the ganglion cells of the medulla. 

 Similarly, reflex extension is effected by the action of the sensory nerve- 

 fibres which pass from the skin of the back into the other sensory ganglion 

 cells of the radial medulla, connecting-fibres between these and the motor 



