MEMORANDA. 287 
powers. Suppose, for example, I have a diatom under the 
microscope; I, in the first instance, place it in the centre of 
the field, and, on introducing the finder, I observe the follow- 
18 
ing figures and lines, |— 
phe} 
we 
; I then register the position of the 
: 103 ee : She ; 
object thus, 53 with a point (*) on the exact position which 
indicates the centre of the field where the object will be 
29° 
20 
I again with a point indicate the exact position of the object. 
Should two or three objects be registered for one field, I mark 
found ; if the figures and lines seen on the finder be thus, 
their position thus, Loar If the field of the finder be divided 
26 |2 NO 
oul » T again indicate the exact position by a dot (*). In 
Newcastle-on-Tyne the mode of using the slide is to place the 
label to the left hand against the stop.—T. P. Barkas, 
Newcastle-on-Tyne. 
Nervous System of Lumbricus.——I beg to draw your atten- 
tion to the fact that I have been misled in my paper on the 
earthworm, in attributing the discovery of the pharyngeal 
portion of the nervous system to Mr. Lockhart Clarke. It 
was briefly described and admirably figured by M. de Quatre- 
fages in Cuvier’s ‘ Régne Animal,’ in the year 1847, whilst 
Mr. Clarke’s memoir was not published until the year 1856. 
I am anxious that the merit of the discovery should be given, 
however small, to its rightful claimant.—E. Ray Lanxester, 
Down. Coll., Camb. 
Beck’s Treatise on the Microscope.—A note from Mr. Lang, 
published in the last number of the ‘ Microscopical Journal,’ 
calling in question some statements on my ‘ Treatise on the 
Microscope,’ requires a reply from me. 
It will, perhaps, be most straightforward to state that one or 
two private communications have passed between us, and I 
am now at liberty to mention that Mr. Lang is quite con- 
vinced of the necessity for some fixed standard when estimating 
magnifying powers. If it were attempted to calculate how 
many times an object were magnified by comparing it with a 
