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specimen referred to by Mr. Smith, he could not give any opinion about it 

 at that moment, but he should like to point out that he had not been quite 

 properly quoted as to having said the " medium." What he said was the 

 " cement," meaning what the diatoms were fixed with, and which sometimes 

 by its contraction would produce granulations which might under some 

 conditions be mistaken for markings. As a general rule the markings on 

 diatoms were regular, or if not so there was some system about them which 

 he might almost call a regularity of irregularity, compared with which the 

 effects of the granulations of cement or other substances would be con- 

 spicuously irregul r. It was in practice very difficult to get rid of foreign 

 matter entirely from a diatom, and frequently, after many attempts, he 

 had given up all hopes of doing so, and on mounting the specimen he found 

 that the irregularity had disappeared under the process when seen in the 

 ordinary way. He thought, however, it was possible that when viewed with 

 a different kind of illumination, under immersion objectives, the irregularity 

 might still be perceived. 



Mr. Karop said as the holiday season was coming on he should not be 

 likely to trouble much about the finer structure of diatoms for a month or 

 two. He thought, however, that the matter of an inner and outer mem- 

 brane was one which might give rise to some misconception, because it 

 might very often be imperfectly silicified, and therefore might by the 

 treatment with acids be unequally acted upon so as to produce appearances 

 which would very likely be mistaken for apertures of different kinds by 

 different observers. 



Mr. Smith said that as the objects were exhibited in the room members 

 could easily see for themselves what had been described. He thought a 

 great deal of the difficulty arose from the imperfect adjustment of the 

 correction collar of the objective. 



Mr. Henry Davis called attention to a fish parasite, Gyrodactylus elegans, 

 which he had found upon some sticklebacks from the River Lea, and which 

 he proceeded to describe by means of drawings on the black board. 



The Chairman said that he was sure the members would be much 

 obliged to Mr. Davis for bringing this subject before them, and he hoped 

 some of them would be able and willing to follow it up. 



Mr. J. D. Hardy said that he did not recognize this creature from the draw- 

 ing and description given, but should be very glad to hear in what part of 

 the Hackney Marshes it could be found. 



Mr. Davis, in reply to this question and also to further questions from Mr. 

 Hardy and Mr. Parsons, said that as regarded the adult forms he could see 

 the development of the hooks taking place in the egg. He did not find the 

 parasites himself, but his little boy got them one day during an expedition 

 with a net and pickle bottle, and having asked to be shown the circulation in a 

 stickleback's tail, he put one of the fish under the microscope for the purpose, 

 and then found it to be infested with the parasites. Having a weakness 

 for Rotifers, he wanted to make this out to be one, but was unable to do so. 



Mr. Morlancl read a paper " On Porodiscus interniptus and Craspedoporus 

 elegans" 



