BULLETIN OF THE UNITED STATES FISH COMMISSION. 361 



salmon (Oncorhynchus quinnat), lake trout (Cristivomer namaycush), 

 grayMng (Thymallus tricolor), and land-locked salmon (Sahno salar, var. 

 sebago). 



IMPEOVED METHODS OF INCUBATING EGGS OF THE WHITEFISH (COEE- 



GONUS CLUPEIFOEMIS). 



Since the Nortkville hatchery was built, the method of incubating 

 whitefish eggs has undergone a radical change. The hatching boxes 

 are still used for the salmon and trout, but for white-fish they have been 

 entirely supplanted by inventions which greatly reduce the expense and 

 labor involved in hatching this species by artificial processes. 



The principles upon which the construction and operation of these 

 later iuventions%re based are substantially alike in all. Whitefish eggs 

 are small and light, and hence are easily buoyed or influenced by cur- 

 rents of water ; and the dead and confervaceous eggs are a trifle still 

 more buoyant. These conditions are taken advantage of by having a 

 proper head of water and releasing a graduated volume under a uni- 

 form pressure on a mass df eggs in a vessel of suitable size and confor- 

 mation to secure the purposes in view. A fixed movement is thus given 

 to all eggs of the same specific gravity, while the lighter eggs of con- 

 fervaceous growth, contact with which imperils the safety of the living 

 embryos, are driven from the presence of the latter by the outflowing 

 current, which carries them out of the vessel or holds them at the sur- 

 face, whence they can be removed en masse at leisure. In the use of 

 the hatching boxes, where the eggs are not kept in motion but remain 

 quiescent, it is necessary to be always on hand with a pair of tweezers 

 to pick away the dead eggs one by one as fast as they become visible 

 on the trays. Hence the hatching of large numbers by the box system 

 involved a great deal of labor and expense, which is now largely dis- 

 pensed with. Constant surveillance and manipulation to keep the dead 

 and living ova separated is no longer necessary, and the actual work 

 demanded to incubate any number of millions of whitefish embryos is 

 now no greater than was formerly demanded for as many thousands. 



The style of improved incubator first brought into use at the North- 

 ville hatchery is known as the Chase jar, and is the invention of Mr. 

 O. M. Chase, of Detroit, Mich. The jar is a cylindrical glass vessel 19 

 inches high by 6 inches in diameter. The water is introduced through 

 a glass tube resting in the center of the egg-chamber, and is released 

 upon the eggs at the foot of the tube, which is slightly raised by three 

 small feet. A tin rim provided with a gate and lip for discharging the 

 water is fitted to the top of the jar, and the whole is placed directly 

 underneath a spigot connecting with the top of the glass tube by a 

 short piece of rubber hose. 



These jars were used at Xorthville during the seasons of ISSO-'Sl arid 

 1881-82, sufficient tank room being provided to operate about 150. 



