60 
WenhAm, on the Vegetable Cell, 
fectly black, with objectives of the most extreme aperture ; 
some DiatomacecB mounted in balsam, are shown with a degree 
of beauty and delicacy, that I have never seen equalled, and 
from the lights brilliantly illuminating the prominences on the 
surface, many of them wear an entirely different appearance to 
the same objects seen as transparencies, and from the absence 
of all irregular refraction and colour, and the purity of the 
vision, the mind is impressed with the fact, that we are viewing 
them under their true features, as cellular structures, and in 
some instances displaying such a singular arrangement and con- 
figuration of markings, in cases where I had not even suspected 
them to exist, that I shall on a future occasion give some 
illustrations of them. It must not, however, be expected that 
all the DiatomacecB can be seen by these methods, for some of 
them, when mounted in balsam, are so exceedingly translucent, 
that they will not hold a sufficient quantity of light, to be 
viewed as strictly opaque objects. 
For this method of illumination, the greatest nicety is 
required in the adjustment of the object-glass, the slightest 
defect in this causing milkiness and indistinctness of vision — 
indeed so particular is the care required in this respect, that a 
different adjustment is sometimes necessary for various parts 
of the same object, in a case where it lies in an inclined 
position in the balsam. 
With regard to the relative merits of the three methods that 
I have mentioned ; for those who are already possessed of a 
parabolic condenser, the preference is most decidedly to be 
given to the hemispherical lens, fig. 4, set in a very thin plate 
of brass, but the truncated paraboloid, fig. 5, is by itself a 
most convenient piece of apparatus, readily applied and easily 
managed, forming a most useful adjunct to the other. 
On the Vegetable Cell. By F. H. Wenham. 
(Read May 28th, 1856.) 
In the ' Annals of Natural History' for May, 1856, there is a 
notice, by Professor Henfrey, relating to my paper on * Cell 
Development,' published in the * Quarterly Journal of Micro- 
scopical Science ' for Jan. 1856. I prefer making my reply 
through the medium of the same Journal, which is accessible 
to all whom the subject may concern. 
The notice commences by saying : — " The essay contains 
internal evidence of the author's want of familiarity with the 
subject treated." It does, in all probability, contain irregu- 
larities and omissions which may possibly be excused in an 
inexperienced writer on these particular subjects. I pretend 
