HYDllA. 173 



After some days he observed several polypes on a part of 

 the glass on which he had not seen them before; and his 

 attention being directed to them for some time, he saw that 

 they could change their position, and that they actually 

 moved from one place to another. This they did somewhat 

 in the way of certain caterpillars, whose mode of walking is 

 to bring the two extremities of the body close to each other, 

 while the middle part is raised like a bow, and then moving 

 the head part, and bringing up the posterior part close to 

 it, by every step they thus advance nearly the length of the 

 body. The polypes made progress in much the same way, 

 by using their arms. Seeing, then, that they could walk, 

 he was, at the moment, persuaded that they were animals, 

 and for some time he paid little attention to them. 



The glass in which they were kept was placed on a table 

 near to the window, and passing it one day, he observed a 

 great number of the polypes on that part of the glass wdiich 

 w^as nearest to the light. Wondering whether this was 

 accidental, he turned the glass half round, so that the 

 lightest part thus occupied was removed into the shade, and 

 the part now exposed to the light was without any upon it. 

 Next day he observed that some had removed to tlie part 

 that was now most exposed to the light, and in a few days 



