TWELFTH ANNUAL MEETING. 43 
In this figure we have shown a pair of jars fitted up, one for 
the hatching of the eggs, the other for the collection of the 
young fish. 
The jar consists essentially of a cylindrical glass vessel with 
hemispherical bottom. These are not blown, but pressed, in 
order to secure perfect regularity of the interior surface, upon 
which depends to some extent the perfect working of the jar. 
The glass foot which is shown in the improvised form has been 
omitted in the form now in use, the jar being supported upon a 
tripod of three glass legs, this form of attachment being adopted 
to prevent the distortion of the bottom of the jar which would 
necessarily result from the attachment of a single foot to it. . 
The top ot the jar is made with threads to receivea screw cap, 
and both the bottom and the top surfaces are ground so that the 
plane of each shall be perpendicular to the axis of the jar, and 
so that when the jar is resting upon its feet its axis shall be per- 
fectly vertical. 
These are all-important considerations to secure the proper 
working. The top of the jar is closed by a metallic disk perfo- 
rated with two 3s-inch holes—one perfectly central, which ad- 
mits the tube that introduces the water into the jar; the other 
equally distant from the central hole and from the edge of the 
plate. A groove in the inner surface of this metallic plate car- 
ries a rubber collar, and when the plate is in place the tightening 
of the metallic screw cap shown in the figure seals the opening 
hermetically. Both the inlet and outlet tubes pass through 
stuffing-boxes, by which means the tubes can be slid up and 
down easily, and tightened firmly in any desired position. The 
construction of the jar is such that when the metallic disk is in 
place the central tube takes the central position necessarily; by 
loosening the screw cap of the stuffing-box, the central tube can 
be slid up or down so as to produce just such movement of the 
eggs as is desired. If the quantity of water entering be small, 
or the head of water slight, without changing the feed of water 
we may vary at will the force and velocity with which it enters 
the jar. By pushing the tube down so as to be almost in con- 
tact with the bottom of the jar, we make a relatively small quan- 
tity of water do the work of a larger quantity in producing mo- 
