8 THE YOUNG 
in different individuals. The cilia are not 
disposed, as at first appeared, in two sepa- 
rate and distinct disks, but are contin- 
uous, as in the annexed sketch. Down 
each side are two long muscular bands, 
Pterodina patina— tail foot. 
distinctly striated, and when they con- 
tract, the ciliary apparatus is drawm in. 
As this contraction takes ]^lace, two ap- 
parently elastic bands, to which the ciliary 
lobes are attached, are bent downwards, 
till they look like the C springs behind a 
gentleman's carriage; and they regain 
their former position of slight curvature, 
when the cilia are again thrust out. 
The gizzard is three-lobed, and cu- 
riously grasped by forked expansions of 
the handles of the hammers. The tail, or 
A. Metopidia aceuminata, as drawn by Mr. Gosse. 
B. Specimen as seen and described in text. c. 
Mouth or gizzard. 
tail-foot, can be withdrawn or thrust out 
at the will of the creature ; and when in a 
good position for observation, a slight ad- 
ditional pressure will keep it so for exam- 
ination. Delicate muscular longitudinal 
bands, forked towards the end of their 
course, supply the means of performing 
some of its motions, and one, or perhaps 
two, spiral threads extend through the 
upper half of its length, and either act as 
SCIENTIST. 
muscles, or as elastic springs for its ex- 
tension. The intestines and other viscera 
are clearly exhibited, and a strong ciliary 
action conducts the food to the gizzard- 
mouth. 
To return to the tail. One spiral fibre is 
easily discovered ; but I have often, and at 
an interval of months, seen the appear- 
ance of two, and am in some doubt 
whether this was a deception, arising 
from the compression employed, or was a 
genuine indication. 
Where this Eotifer occurs I have usually 
found it plentiful, but unfortunately could 
obtain no constant supplies after I had 
determined to make a special study of the 
remarkable tail, which is much more 
complicated than I have described. The 
Pterodina lived for some time in captivity, 
and for a week or two I could obtain them 
from my glass tank. They w^ere likewise 
to be found for some weeks in the same 
part of the pond, but not all over it, until 
one day not a single specimen could be 
discovered, notwithstanding a persever- 
ing search, nor was I afterwards able to 
get any from that pond during the re- 
mainder of the year. 
Makeshifts for Young Microscopists. 
IN the earlier numbers of the Young 
Scientist several simple pieces of mi- 
croscopical apparatus were described, 
amongst others a very simple and effec- 
tive substitute for the stage forceps, and a 
cheap bull's-eye condenser. I have lately 
made for myself several pieces of acces- 
sory apparatus, from which I get very 
good results, and it has occurred to me 
that it might be well to describe them for 
the benefit of my fellow readers. Amongst 
other pieces I have made a dark-ground 
illuminator w^hich works very well, al- 
though it cost me actually nothing, except 
a little w^ork, and a polariscope which 
cost me $2.50, and by which I get as beau- 
tiful effects as those produced by some of 
my friends who have paid $15 and $25 for 
their polariscopes. Of course in these 
estimates of cost I do not count my own 
time and labor, for I regard the making 
of these things as so much pleasant recre- 
ation. 
One of the most useful accessories to 
the microscope is the bull's-eye condenser, 
as it is called. This consists of a lens of 
short focus and large diameter, which is 
used after the manner of a burning lens ; 
that is to say, it is used to throw a bright 
