340 



it likely that there should have been an abrupt junction between a closing 

 membrane and the sides of the spaces below as Mr. Deby had drawn. He 

 thought on a priori grounds there wouid have been a thickening at the 

 angles. 



Mr. Deby thought this argument was rather of a theoretical than a prac- 

 tical character, but he thought if they took a section of one of the joints of 

 Spirogyra they would find that the closing membranes formed right angles 

 with the sides of the filiform space. 



Mr. Morland had found it to be invariably the case that there was a 

 thickening at the angles as drawn by Prof. Stewart. 



Mr. J. E. Ingpen said that at that late hour he would not trouble the 

 meeting with more than a short communication upon the subject of mount- 

 ing in media of high refractive index, the basis of which was sulphide of 

 arsenic. It would no doubt be recollected that some time ago some very 

 beautiful specimens of this kind of mounting were sent over to this country 

 by Prof. Hamilton Smith. Mr. William Meates set himself at that time to 

 find out what the medium was which Prof. Smith had employed, and after 

 some amount of experimenting he came* to the conclusion that it must be 

 some preparation of sulphide of arsenic. Prof. Smith at first would not 

 publish the formula, but when at length he was induced to do so, it turned 

 out to be a mixture of sulphide of arsenic in bromide of arsenic. Mr. 

 Meates then went on to experiment as to how far the effects could be varied, 

 and he obtained a medium of very high index indeed, but be found that it 

 had a very high melting point, and that this was greater in proportion to the 

 quantity of arsenic. The results obtained were so good that Mr. Meates was 

 encouraged to continue his experiments, especially as the medium was found 

 to be very useful for mounting other things than diatoms. Blood globules 

 were seen to advantage in it, but he had not yet been so successful as he hoped 

 to be with podura scales. He had brought for exhibition a specimen of sul- 

 phide of arsenic ; also a mount of the Cherryfield Rhomboides in phos- 

 phorus and bi-sulphide of carbon, the colour of which under the microscope 

 appeared to be nearly a brick red, the colour in pure phosphorus being 

 more green. Specimens mounted in sulphide of arsenic, styrax, &c, were also 

 exhibited. 



Mr. Deby said that he found that Prof. Hamilton Smith's medium was not 

 be trusted for permanent mounting. He had a number of slides prepared 

 with it, and about 90 per cent, of these bad become spoilt. It was a most 

 valuable preparation for purposes of examination, but it would not stand 

 the test of time. 



Votes of thanks to Mr. Morland, Mr. Deby, and Mr. Ingpen were then 

 passed, and the meeting terminated with the usual Conversazione. 



The following objects were exhibited : — 



Living Barnacles, B alarms balanoides ... ... Mr. F. W. Andrew. 



Larva of Tettigonia (spring frog hopper) ... Mr. C. Collins. 



Head of Colletes Daviesana (Ground Bee) / 



.,,,,,. \ Mr. F, Enock, 



with explanatory drawing ... ... ; 



