344 
NOTES AND MEMORANDA. 
are so few and irregular, as only to suffice for tbe identification of tlie 
species. Regular feeding with water containing abundant food pro- 
duces a corresponding increase in their number and regularity, and a 
supply of carmine and indigo on alternate days is followed by the 
deposition of very regular alternate layers of red and blue courses on 
the outside of the tube. . . . 
My specimens produced abundant ova, which were formed in the 
usual manner in the ovary, and thence extruded into the space between 
the animal and its theca, and deposited upon the lower part of the 
foot, as is customary with this division of the Rotifera. I have not 
yet observed their development, nor, although I have examined a 
large number of sjDecimens, have I yet been fortunate enough to see 
the male of this species.”* 
Cutaneous Glands. — On page 261 of ‘Huxley and Martin’s 
Elementary Biology,’ in treating of the skin, it is stated that the 
mouths of the cutaneous glands are seen as claer round spots, 
although their openings are really tri-radiate. No directions are 
given for demonstrating that aj^pearance, but it may be done veiy 
nicely by putting a bit of skin from a frog’s back or side into Muller’s 
fluid one part, water four parts (any weak solution of a chromium com- 
pound would do very well), for two or three days. The layers of the 
epidermis come apart, and the external layer shows perfectly the tri- 
radiate openings of the glands. If this layer be coloured in carmine 
or picro-carmine, it makes a very pretty and instructive object ; for it 
not only shows the mouths of the glands, but the large flat nucleated 
epidermal cells. Professor H. H. Straight, of the Oswego Normal 
School, says, “ If a live frog be wiped dry with a cloth, and then put 
into water overnight, the external layer of ei^idermis comes off very 
readily,” that is, the frog has been made to cast its skin. By making 
use of this process the points mentioned above might be demonstrated 
w ithout hurting the frog.j 
“ Limits of Accuracy in Measureumit ivitli the Microscope.'" — A 
paper with this title, read at the Indianaj)olis Congress by Professor 
W. A. Rogers, concluded as follows : — 
“ I think we may safely draw the following conclusions from this 
investigation ; 
1. Two equally skilled observers can measure the same space 
within about oVo o inch, if the space does not exceed of 
an inch. For a space of of an inch the deviation will probably 
amount to -go^oo" inch, in case the measurements are made with 
an eye-piece or a filar micrometer. 
2. The average deviation for accumulated errors, under similar 
conditions, is not far from 5 eleven intervals. For 
a large number of intervals the deviation will be somewhat larger, but 
it will not be proportional to the number of intervals. 
3. A single observer can obtain an agreement with a normal equa- 
tion representing all the observed values as far as a solution by least 
* ‘ Midland Naturalist,’ vol. i. p. 302. 
t Mr. Gage, in ‘ American Quarterly Microscopical Journal,’ vol. i. p. 72. 
