ON THE PHYSIOLOGY OF ECHINOHERMATA. 131 



Observations on the Physiology of Echinodermata. By 

 George J. Eomanes, LL.D., F.E.S., Sec. Linn. Soc. 



[Read March 1, 1883.] 



Continuing the observations on the nervous system of Echino- 

 dermata which some years ago I began in conjunction with my 

 friend Professor J. Cossar Ewart*, and then communicated to 

 the Koyal Society, I have thought tbat, being now Secretary of 

 this Society, it may be more fitting that I should communicate 

 to it the results of my f artber inquiries. 



In the paper already published by the Eoyal Society, it was 

 shown by experiment that the ocelli situated at the end of the 

 rays in Starfish, and occupying the homologous position in Echini, 

 perform a visual function — inducing the animal to seek the light 

 so long as the ocelli are intact, and the animal ceasing to be 

 aff'ected by light when the ocelli are removed. It therefore 

 occurred to me to try whether tliese organs of special sense 

 might not have an olfactory as well as a visual function to 

 perform. In order to try this, I procured some fresh starfish, 

 and having placed them on a flat surface covered with shallow 

 water, I dropped little pieces of limpet and crab in their vici- 

 nity. None of them, however, approached the food. Knowing 

 that starfish appear to be guided to fishermen's bait by a sense 

 of smell, I thought this result unsatisfactory ; and supposing it 

 possible that, having been freshly caught, they might not be in 

 want of food, I left them in a tank for a couple of days, and 

 then repeated the experiment. The result was now quite dif- 

 ferent, for the starfish began actively to crawl in the direc- 

 tion of the food. Selecting one individual and putting it in 

 a large dish which was filled with sea-water, I found that I 

 could at pleasure lead the starfish in any direction I chose by 

 holding a morsel of crab an inch or two from the end of 

 one of its rays, and continuously withdrawing the food as the 

 starfish continuously approached it. Moreover I could at any 

 time reverse the direction of advance by transferring the food to 

 the opposite side of the animal, and holding it for a sliort time 

 near the tip of a ray. Thus I could entertain no doubt that 

 starfish have a well-developed sense of smell, which enables 



* See tlie Crooniau Lecture, 1881, Philosopical Transactions, pt. iii. 1881, 

 pp. 829-885, 



