20 
Since the last meeting, he had had an opportunity of carefully 
examining, through the courtesy of Mr Curties, a series of Gundlach’s 
lenses, ranging from a} toa 1-24th. The 4 and } were not good; the 
4 was a perfect lens ; the same might be said of the 1-12th and 1-16th. 
The latter, which was on the immersion principle, was especially 
useful, as giving 600 diameters with a low eye-piece and working 
through thick glass and balsam. No recent additions to the micro- 
scope had equalled this lens as an instrument of research in minute 
Natural History. The 1-12th’s, though very good, yet being dry lenses, 
approached nearer than the 1-16th’s, and were in magnifying power 
equivalent to a Ross’s 1-8th ; they worked through thick glass, and 
were not inferior to any lenses he had seen, though Ross’s 1-8th was 
superior on P. Angulatum. They would be very valuable to those 
who did not possess English lenses of this power, especially as in the 
whole series, the objectives are about one-third the price of English 
ones. Finding the first specimens so good, he had asked Mr. Curties 
to send others, so that they might be able to judge if the supply would 
be equal to the specimens first sent. As far as he had been able to 
judge, they were still of the first-class ; but he would suggest that the 
objects to be shown should be seen with Gundlach’s lenses, and com- 
parison be made with other objectives by the Members present. He 
felt personally indebted to Mr. Curties for his kindness in allowing him 
time for a fair judgment, and thought the members, as microscopists, 
were under an obligation to him, for the opportunity he had afforded 
them. 
Mr, Wonror then introduced the subject for the evening, ‘‘ Shell 
Structures,” by describing the structure and component parts of the 
shells among the Mollusca, at one time supposed to be mere inorganic 
exudations, cemented together by animal glue. It is now known that 
their shells are composed of animal and calcareous matter, the former 
constituting a membranaceous basis, forming cells, with hexagonal 
walls or of lamine, more or less wrinkled ; some shells were traversed 
by tubes, others by canals, with trumpet-shaped orifices ; in each cage 
the calcareous matter gave solidity to the membranaceous tissue. 
The internal layer, of a nacreous nature, in many was very beautiful. 
Some of the porcellaneous shells were made up of three distinct layers 
of a similar structure. In the Crustacea, especially the crab, four 
layers could be distinctly made out, one of which strongly resembled 
dentine, except that the tubu/i did not branch, but remained of the 
same size throughout their course, It was in the cellular layer where 
