( 326 ) 
[Monthly Microscopical 
Journal, Dec. 1, 1869. 
PKOGKESS OF MICKOSCOPICAL SCIENCE. 
The Douhle Plate of Aulacodiscus oreganus. — From tlie proof- 
sheets of the Proceedings of the Boston Society of Natural Science 
which have reached us, we learn the following particulars of some 
communications on the above subject made to that Society in the 
course of this session by Mr. R. C. Greenleaf. Referring to the fact 
that Mr. Charles Stodder had already called attention to the double 
plate of the various disk forms among the diatoms, he mentioned that 
Mr. E. Samuels, in preparing a single specimen of Aulacodiscus orega- 
nus, after placing it on the slide, found that it had divided, the upper 
shell slipping off from the under. This, he said, is the most perfect 
specimen of the division of this class of diatoms he had ever seen, and 
the most authentic, as the divisions really took place under the eye. 
This is a very interesting object, because it proves, if proof were 
needed, that these disks are formed of two shells, and thus conclu- 
sively reveals the fact that many species have been named by micro- 
scopists as new, that are only the thin under-layers of the shells of 
species already classified. Mr. Greenleaf is confident that many 
of the species named by Dr. Greville, although he was one of the 
most skilful and diligent of observers, are merely these thin shells 
removed from their connections. In the January number of the 
' Quarterly Journal of Microscopical Science,' there is a figure given 
by Dr. Greville exactly like this under-shell, which he calls Aulaco- 
discus orientalis. Since writing the above remarks Mr. Greenleaf had 
seen a letter from Professor Eulenstein to Mr. Charles Stodder, in 
which he alludes to the paper of Dr. Greville on Aulacodiscus orien- 
talis. Professor Eulenstein at first thought, as he did, that A. orien- 
talis was the inner plate of A. oreganus, but after a more careful 
examination of the form, decided it was a new species. He had a 
slide containing the object. Mr. Greenleaf had only seen the drawing. 
Mr. Stodder is of the same opinion. He says that the granules in 
A. orientalis differ in form from those of A. oreganus, being square or 
oblong, and not arranged exactly in the same order. This last vari- 
ation Mr. Greenleaf noticed in the drawing, but by a careful adjust- 
ment of the focus, the variation in this particular is small. Professor 
Eulenstein says there is a chance of error in examining these disk 
forms, in mistaking an immature frustule, separating from the parent, 
for the inner plate. Mr. Greenleaf would be inclined to hold to his 
first impression, but said he must defer to higher authority at present. 
The Preservation of Sections of Brain and Spinal Cord. — Concern- 
ing Dr. Bastian's paper on this subject, which appeared in one of our 
earlier numbers, Mr. Alfred Sanders, M.R.C.S., has addressed the 
following letter to ' Scientific Opinion ' (Nov. 24th) : — • 
" Allow me to call the attention of those of your readers who are 
interested in microscopical investigations, to the use of creosote for 
this purpose : it was recommended by Dr. Ludwig Stieda, in Max 
