NATURAL HISTORY MISCELLANY. 735 
by a revolving diaphragm placed between the lenses in the place 
where the diaphragm is usually placed in an eye-piece. There are 
three holes of different sizes for direct light, one hole with a central 
stop for dark field, which gives an admirable effect with objectives 
under 30°; and two oval openings, and one oblong opening espe- 
cially for the binocular. The oval openings are opposite each 
other and are in use at the same time, giving two oblique pencils 
of light, converging to a point, and which are very useful for the 
binocular. This condenser was used with various objectives from 
14 inch ta = of an inch, giving ample light for the latter with 
the highest eye-pieces. 
Mr. Bicknell stated that with this condenser and a 4 of only 
100° aperture, he had seen the same test object which had required 
al; or a 7 of 150° when used without it. 
Tue Srare Microscoricar Soctrery of Illinois has issued a pro- 
spectus of “ The Lens,” a Quarterly Journal of Microscopy and 
the Allied Natural Sciences: with the Transactions of the State 
Microscopical Society of Illinois; the first number to appear on 
the first of October. It will be an octavo, each number containing 
at least forty-eight pages of reading matter. Terms, two dollars 
per annum in advance. Address Charles Adams, Secretary of the 
Publishing Committee, 1000 Michigan Avenue, Chicago, or the 
the Editor, S. A. Briggs, 177 Calumet Avenue, Chicago. Though 
its appearance has been delayed by the fire, we learn that it will 
soon be issued. 
Tue Use or THE MICROSCOPE IN STUDYING THE EMBRYOLOGY OF 
THE SKULL. — His work had not direct reference to the subject 
of teleology, nor to the structure of the tissues ; but his object had 
been to work out the metamorphosis of the skull, and to see the 
tissues as they begin to differentiate and modify to form the em- 
bryo. The subject was a very large one, and had been principally 
labored at by the great German embryologists. He had spent 
the last two years in studying the development of the frog’s skull, 
in watching the different and numerous stages which that creature 
undergoes, and the relations it bears to other creatures of the ver- 
tebrate type, always remembering that the frog was essentially a 
fish. He had been in some degree unprepared for the extent of 
the metamorphic changes that the frog underwent. He had worked 
out this subject into ten artificial stages, the first of which he had 
obtained when the frog was in the egg. In the first stage of its 
