MICROSCOPY. 245 
Naid family which abounds in pools near Canterbury. The vivid 
action of the vibratile cilia within the intestines, causing a rapid 
current of water, was seen in the pellucid segments of the thin, 
flat body, and was regarded as a true respiration. The same may 
be seen in Sanuris variegata. 
DeveLorment or Hyprovicryon.— Mr. Keit, of the Dublin 
Microscopical Club, obtained, by cultivation, two forms of this 
plant, an irregular network of large cells, and the ordinary nets 
which “appeared ” to be produced from the irregular form. Fur- 
ther study is promised. 
Tur Marrwoop Fixper.— This little accessory, used by almost 
every microscopist, is used under two disadvantages, the want of 
exact correspondence in position of the scales on different plates, 
and the size of the squares, in one of which, under a high power, 
an object may still be lost. Mr. W. K. Bridgman offers, in the 
“Monthly Microscopical Journal,” a means of correcting these 
difficulties, 
Each person using the finder in exchanges, is advised to prepare 
‘common slide with a label in the centre and a dot on this, indi- 
cating the position of the centre of the central square of his own 
Finder. This “ test slide,” properly named, may be sent to any 
correspondent as a key to the correction if any, to be made in 
Using his Finder. 
The position of an object in a square must be recorded, or 
much of the usefulness of the Finder is lost. Mr. Bridgman 
indicates this position by a dot having the same relation to the 
figures. Thus 2.5 would indicate that the object was situated in 
the centre of the square 235, or 2°. that it was far to the right of 
_ the centre. The writer (R. H. W.) has always been accustomed to 
record the position in the square by decimals; as, in the cases 
above, 33:2 and 25:9, This plan, which is convenient, and not 
liable to mistakes, has been mentioned to many persons, and 
doubtless used independently by many more, but is not recollected 
to have been published before. It is accurate to within one-tenth 
Of the diameter of a square, which is quite sufficient in practice ; 
but two places of decimals may be used, if deemed necessary, to 
ndieg iti . 25. . 25-99 
Andicate positions very near a line, as 85:2! or 3375. 
