698 ; MICROSCOPY. 
of the wings of the golden plover and of the woodcock were found 
to be especially suitable. : 
Repropuction or Dxsmips.—Prof. Leidy, at a late meeting of 
the Academy of Natural Sciences of Philadelphia, made some re- 
marks on the mode of reproduction and growth of the Desmids. 
In illustration he described a common species of Docidium or Pleu- 
rotenium. This consists of a long cylindroid cell constricted at 
the middle and slightly expanded each side of the constriction. 
When the plant is about to duplicate itself the cell-wall divides 
transversely at the constriction. From the open end of each half- 
cell there protrudes a colorless mass of protoplasm defined by the 
primordial utricle. The protrusions of the half-cells adhere to- 
gether and continue to grow. The bands of endochrome non 
extend into the protrusions and subsequently keep pace with their 
_ growth. * The protrusions continue to grow until they acquire the 
length and form of the half-cells from which they started. : The 
exterior of the new half-cells thus produced hardens or becomes 
a cell-wall like that of the parent half-cells. In this condition 
two individuals of Docidium are frequently observed hefore mers 
aration. During the growth of the new half-cells the circulation 
of granules in the colorless protoplasm is quite active. In a spe 
cies of Docidium 14™ long by ~;™™ broad, the growth of the new 
half-cells was observed to be at the rate of about $™™ in an hour. 
ANGULAR Apertures.—It is not yet forgotten that at the Lon- 
don examination of the 4 inch lens sent to demonstrate the ma 
sibility of obtaining an excessive angular aperture in immersion 
work on balsam objects, the lens was measured at an adjustment 
of which nothing to the point was known except that it was not a 
position of immersion work at all, nor a recognized maximum PO 
sition for any kind of work; the plain fact being that the er 
plished committee were so bent upon teaching us the familiar fact 
of reduced angle that they seem to have forgotten to look for any 
other possibility in the case. Nor is it likely to be forgotten J 
long as Mr. Wenham so far forgets his usual and admirable pae 
as to allude to the correction of this palpable mistake as an 
quibble,” nor while the eminent President of the Royal Microscop- 
ical Society utters in his formal address such an astounding "a 
ment as the following :—*“ The lens in this instance was proper e | 
corrected as a dry lens, and then after measurement in air iY 
