334 PROCEEDINGS OF THE SOCIETY. 



collection so large as that of Mr. "Watkins a great amount of exjierience 

 in mounting must have been obtained, and be should therefore like to 

 ask what kind of medium had been found best for the purpose, lie had 

 a number of slides of this kind, but his experience was like that of most 

 other persons, that after a lapse of time a great many specimens became 

 deteriorated : but he had some which were said to be mounted in 

 "Suffolk" — whatever that might mean — and these were all in most 

 excellent condition, both as to tbe way in which they were displayed 

 and that in which they had retained their characters. 



Mr. Cooke said, with regard to the character of the teeth as indi- 

 cating the nature of the food, so far as the land mollusca were concerned 

 there was a very marked distinction, the carnivora being conspicuous 

 by having teeth with sharp arrow-like points ; but in the case of slugs, 

 which generally ate animal matter, but which would also eat anything 

 else, and would even eat one another if other things failed, the radula 

 presented a curious mixture of the sharp arrow-like forms with others 

 of a squarer form approximating to that of the vegetable feeders. He 

 could not say with certainty that the marine Mollusca fell into the same 

 classification, because, more especially in the case of deep-sea varieties, 

 it was difficult to say what their food really consisted of. As regarded 

 mounting, all the preparations from which the photographs were taken 

 were mounted in glycerin jelly. 



Mr. Suffolk disclaimed all knowledge of the peculiar medium men- 

 tioned by Prof. Stewart ; but as he had been advising for a number of 

 years upon questions of mounting, it was just possible that it might be 

 something which he had at some period recommended. 



Mr. E. M. Nelson exhibited and described a new form of mechanical 

 stage, in which two points were moved by milled heads in rectangular 

 directions, carrying the slide with them, the slide being pressed against 

 them when they were withdrawn by the hand. 



Mr. Crisp said it seemed to him to be a very great disadvantage not 

 to have the object follow the mechanical movements in both directions. 



Mr. Michael said he should not like to have to use a stage on this 

 principle, at any rate for the work in which he was chiefly engaged. 

 He could not agree with what Mr. Nelson had stated as to the side move- 

 ment being seldom wanted ; for his own part he thought he used it more 

 than he did the other. 



Prof. Groves thought that one great disadvantage in the arrangement 

 was that it necessitated the use of both hands to manipulate the slide, 

 whereas the great advantage of the ordinary mechanical stage was that 

 it left one hand free for focusing at the same time that the slide was 

 being moved. 



Mr. Crisp said that this, to his mind, was the fatal objection to 

 Mr. Nelson's device, which really required three hands to work it 

 properly. 



Mr. C. L. Curties exhibited a new Combination Condenser, which 

 in addition to the condenser also contained an iris diaphragm, a spot- 

 lens, and a polarizing prism. It would, of course, like all " Combina- 

 tion " apparatus, be only used where portability was a desideratum. 



