PROCEEDINGS OF THE SOCIETY. Ill 



frequently met with a kind of true parasitism. It was also quite a 

 common thing to find Hydrozoa and other things attached to the 

 sj)ouges. 



Dr. Matthews said that he spoke with diffidence on the question of 

 parasitism. He had a number of specimens to show after the meeting, 

 and which he thought would help to elucidate the question. 



On the motion of the chairman, a vote of thanks was passed to 

 Mr. Sollas for his paj)er, the chairman saying he thought it had not 

 been of any less interest from having been the means of eliciting the 

 very interesting communication of Dr. Matthews. 



Dr. J. Edmunds read a " Note on a Revolver Immersion Prism for 

 Sub-stage Illumination," the subject being illustrated by diagrams, and 

 by the exhibition of the apparatus described (see p. 32). A discussion 

 ensued between Mr. Lettsom, Mr. Mayall, and Dr. Edmunds. 



Mr. John Mayall, jun., read a paper " On Immersion Illuminators," 

 various kinds of which he exhibited in illustration of the paper (seep. 27). 



The Chairman inquired if Mr. Mayall had tried mounting objects 

 otherwise than in balsam, because it appeared to him that water might 

 be a very good medium. 



Mr. Mayall said he had been working mainly upon objects in 

 Canada balsam, but he had sojne time ago the opportunity of exami- 

 ning some of Professor Tyndall's bacteria, which were in water, and 

 he then saw very clearly with the immersion what Mr. Dalliuger had 

 the greatest difficulty in making out. 



The Chairman thought that the greater diffijrence between the 

 refractive index of diatom silica and water, as compared with balsam, 

 would probably render the structure more visible if water was used. 



Mr. Mayall said he remembered to have observed that such was 

 the case. 



The Chairman said that they had another paper by Mr. Mayall, 

 " The Aperture question," and one by himself, " On a Catojitric Im- 

 mersion Illuminator " (see p. 36), which must be taken as read, owing 

 to the press of business before the meeting. 



Mr. Crisp explained the views of Mr. Julien Deby in the paper he 

 had sent entitled " Is not the rotiferous genus Pedalion of Hudson 

 synonymous with Hexartlira of Ludwig Schmarda?" Dr. Hudson's 

 drawings of Pedalion and that of Schmarda being laid before the 

 meeting. 



Mr. Stewart read part of a paper by Mr. Kitton, on " The Thallus 

 of Diatoms," accompanied by comments on the views expressed by 

 Dr. Lanzi and Mr. Kitton (see p. 38). 



Mr. Crisp gave an account of the observations of Professor Graber, 

 of Czernowitz, on some new sense-organs (supjjosed to be auditory) 



