150 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



The overflow from tlie collectors is guarded by a wire-gauze or cheese- 

 clotli strainer. A safe and intercliaugeable device consists of a stout 

 wire frame, over which a cheese-cloth bag is drawn and tied, A 

 finch rubber hose is attaclied to the opening in the frame. The 

 strainer is j)ut inside among the fry, and the outflow in an overflow cup. 

 The overflow cup is set at the proper height to control the water level 

 in the collector-tank. Long-handled nets of -jn-inch mesh are required 

 to remove egg lumi)s or other matter from the jars. 



THE AUTOMATIC HATCHING-JAR. 



The United States Fish Commission, in the development of its 

 work, had presented to it the necessity of dealing with the eggs of the 



whiteflsh and the shad upon a 

 scale unprecedented in the his- 

 tory of flsh-culture. Millions 

 were to be handled instead of 

 thousands, and the removal of 

 dead eggs by hand picking was 

 no longer to be considered. 

 After successive experiments 

 the McDonald automatic hatch- 

 ing-jar was devised, and it is 

 now generally employed. 



The most meritorious feature 

 of this apparatus is that it 

 prevents the development of 

 the saproleguious fungus, which 

 caused so great a mortality in 

 some other forms of hatching 

 contrivances in which all the ova 

 were not in continual movement. 

 The very gradual, gentle, and 

 continual rolling movement of 

 the ova ui^on each other in the 

 jar apparently prevents the 

 spores of the fungus from ad- 

 hering. The cleanliness of the apparatus is also advantageous, and as 

 the material of which it is made is glass, the progress of development 

 can be watched satisfactorily from the outside of the jar with a hand 

 glass or pocket lens of moderate power. 



The jar consists of a cylindrical glass vessel, of 7 quarts' capacity, 

 with hemispherical bottom, supported upon three glass legs. The top 

 is made with threads to receive a screw-cap. It is closed by a metallic 

 disk, perforated with two holes five-eighths inch in diameter — one in 

 the center admits the glass tube that introduces the water into the 

 jar, the other, equally distant from the central hole and the edge of 



Automatic shad-batching jar. 



