76 PHILOSOPHICAL TRANSACTIONS. [aNNO 1744. 



In one case where the polypi are simple, they are not above the 240th part of 

 an inch irt length, and are of a shape nearly resembling that of a bell : one of 

 these is represented exceedingly magnified, fig. 1, pi. 2. The anterior part, ac, 

 generally appears open, when it properly presents itself; the posterior part ib is 

 fixed to a stem or pedicle be; and it is by the extremity e of this pedicle, that the 

 polypus fastens itself to any other sort of body. The polypus of this sort generally 

 appears to the microscope of a brownish colour, excepting at its smaller end b, 

 where it is transparent, as well as its pedicle be. When the anterior part ac is 

 open, we may perceive about its edges a very lively motion ; and when the polypus 

 presents itself in a certain manner, it discovers, on either side of these edges of its 

 anterior part, somewhat very much resembling the wheels of a little mill, that 

 move with great velocity. These polypi are able to contract themselves; and they 

 do so often, and suddenly. They may be brought to contract at any time, either 

 by touching them, or by moving the body to which they are fixed. When they 

 contract, the edges of their anterior parts are drawn quite into their bodies; 

 and when they resume, which they do soon after, their former posture, we 

 distinctly see those edges come forth again, and put themselves in motion, as 

 before. 



On observing the anterior parts of these polypi, which are open, and whose 

 edges are in motion, we may often remark a number of very minute bodies swim- 

 ming in the water, that seem to be forced down with velocity into these openings 

 of their anterior parts, and which sometimes are thrown out again from thence. 

 To make this observation the most sensible, it is best not to look at a single 

 polypus, but a cluster of a number of them together. 



Though the polypi of the sort in question appear of a brownish colour when 

 viewed with the microscope, yet, having left some of them for several days in the 

 same water, they by degrees lost their brown colour, and became transparent; 

 excepting only that a few grains or spots, of brown or black, still continued to be 

 discernible in their bodies : but having afterwards removed these polypi into other 

 water, newly taken out of a ditch, they in a little time resumed the same brown 

 hue which they had before. 



It may commonly be observed, that when the polypi are in water newly put to 

 them, there fall upon their anterior parts far greater numbers of the above- 

 mentioned minute bodies, than when they have been left for any time in the same 

 water. It is ver)' probable that these minute bodies are exceedingly small animal- 

 cules, on which the polypi feed; and that consequently the opening, which they 

 have in their anterior part, serves them for the purposes of a mouth. 



The polypi that have become transparent, and that have been left some time 

 without the addition of such water as would make them recover their brown 

 colour, have also, at the same time, left off multiplying. But others of them, 



