[13] ARTIFICIAL PROPAGATION OF FISH. 503 
and glass sticks. But as these frames are intended to be put one over 
the other, the box must be somewhat higher than in the trough appara- 
tus, and at the ends there must be large notches for the free passage 
of the water. To render the process 
easier, their surface must not (if the 
» box has the length mentioned above) 
ii) represent more than one-fourth of its 
He a \\\|4 capacity, so that four of them may be 
SEE” on the same floor. 
Fia. 16. This box, which should be used inrun- 
ning water, can be used for free eggs and for eggs adhering to foreign 
bodies. In spite of its small size, it can hatch a very large quantity of 
eggs, and permits manipulations, which in the ‘sieve apparatus” are 
. difficult or hurtful. For 
the purpose of observing 
what is going on inside, and 
to clean the gratings when 
they have become ob- 
structed by sediments, the 
lidsand doors can be opened 
as often as desired, without 
taking the apparatus out 
of the water and without 
disturbing the frames and ==== 
the eggs. Whether at- === 
tached to a floating frame 
by clamps or by strings at- 
tached to pegs driven in the 
ground, it must present to Fic. 17 
the current one of its extremities when the current is moderate and one 
of its angles when it is very rapid. A bed of pebbles and fine sand 
placed at the bottom receives the young fish, which either fall or de- 
scend on it as they are hatched, and offers them favorable conditions for 
their further development, till the time arrives when the gates can be 
opened and they can be set at liberty in some river or pond. Fish of 
small size will escape through the meshes of the wire grating and dis- 
perse through the water. 
When the hatching process is finished, all the frames are removed 
from the box, so that it can be cleaned, and better care can be bestowed 
on the young fish imprisoned in it. 
Whenever it becomes necessary to place one or the other of the above- 
mentioned apparatus in stagnant water, the bottom should be covered 
with aquatic plants, to prevent this water, which of coutse is notrenewed, 
from spoiling, and form an inexhaustible source of oxygen, which is so 
useful for the development of the embryo. 
Wherever propagation is to be carried on on a large scale, it will be 
