146 



Wheatstone, but they could never come to any satisfactory conclusion. Dr. 

 Wallich had made a condenser to produce a certain arrangement of the 

 illuminating raysj and if it proved that by the use of this they could 

 employ lenses of larger aperture and still get the same depth of focus, it 

 would be of very great value. 



Mr. F. Parsons read a paper " On a Hydroid Polyp found in the tank at 

 the Royal Botanic Society's Gardens, at the Excursion of the Club in April, 

 1884," the subject being illustrated by drawings and by enlargements from 

 the same on the black board. 



The President said the drawings would give a better idea of the or" 

 ganism than what was on the board ; there did not seem to be any appear- 

 ance of tentacles. 



Mr. Hardy enquired if Mr. Bourne had seen the drawings ? If not, how 

 did he know the polyps were the same ? 



Mr. Michael asked for what length of time any individual polyp had been 

 watched ? because it was quite a usual thing to find that the first form had 

 only the rudiments of tentacles, which came afterwards by a process of 

 growth, and unless the specimens were kept under observation it was not 

 possible to know that they might not have tentacles at some later period of 

 their lives. 



Mr. Parsons said he had only looked at one polyp during one evening and 

 had not isolated it for continued observation, but although he had looked at 

 a great many he had never seen such a thing as a tentacle. Still it was 

 quite possible that they might subsequently develop. 



Mr. Michael said it was of course quite possible that they might not do 

 so, but it would, he thought, be a little premature to say they never would. 

 It was often very easy to get these organisms to grow to a certain extent, 

 and then from want of favourable conditions nothing further could be got. 

 He should be inclined to say that as far as their information went at present 

 they did not know what might be the ultimate form, and therefore it would 

 be premature to say it never would have tentacles. 



Mr. Parsons said he should be very glad to be able to ascertain the facts 

 and would keep a look out with that idea. It was, however, a very difficult 

 matter to carry out. 



A Member enquired if Mr. Parsons had found that each arm of the bifid 

 or trifid form was distinct from the others, or was there any connection be- 

 tween them ? 



Mr. Parsons could not say, but he rather imagined that there would be a 

 constriction formed, and after that they would separate. He conld not say 

 if there was a canal between them. 



The President proposed a vote of thanks to Mr. Parsons for his com- 

 munication. It was known to all that this matter was one of very great 

 interest to naturalists, because the discovery of a fresh water medusa 

 caused at the time a very great sensation, and it was always felt that a 

 hydroid polyp ought to be found. It was no more than a surmise on the 

 parts of Mr. Bourne and Professor Lancaster at present, and therefore Mr. 

 Parsons had the credit of having seen it first. It was a curious thing that 

 it should be found in another tank beside that at the Victoria Regia house, 



