BULLETIN OF TIIK UNITED STATES FISH COMMISSION. 19 



If a few eggs are cut from the swimmerets of a lobster and dropped into 

 ajar of water, they will rapidly sink to the bottom, showing that their 

 specific gravity is considerably' greater than that of water. The knowl- 

 edge of this fact led to the selection of the McDonald autonaatic hatch- 

 ing-jar, which has lung been in use in shad propagation, for the first 

 experiments, and a trial of about two months has demonstrated its 

 superiority for this purpose over the other appliances that were tested. 

 The i^rinciple on which the McDonald jar works has already been fully 

 described,* and we need only mention here, for the purpose of showing 

 its adaptability to the eggs in question, that the water entering through 

 a long glass tube, reaching nearly to the bottom of the jar, causes an 

 upward current of water through the jar, the force of which is regu- 

 lated by the amount of inflow; the outlet is by means of a short tube 

 passing only a little way into the upper part of the jar. The inlet tube 

 is connected by rubber tubing with a supply pipe, and the outlet tube 

 in the same manner with a waste pipe, and these connections being 

 made, the movement of the eggs is entirely controlled by means of a 

 stop-cock and the longer tube, the latter, by being raised or lowered, 

 changing to a certain extent the force and character of the current. 

 The flow is continuous and regular, and the jars need to be examined 

 only occasionally, perhaps twice each day, for the purpose of forcing out 

 the accumulation of sediment, as explained further on. 



The eggs are readily cut from the swimmerets and under surface of 

 the lobster by means of small sharp scissors, the curved kind used in 

 dissecting being especially well adapted to this purpose, although most 

 any kind will answer. By taking ordinary precautions no harm is done 

 to the parent, the small threads joining the eggs to the body having no 

 organic connection with it. Most of the eggs come off in bunches of 

 variable sizes, some containing two or three hundred, and others less, 

 down to a very small number, but more or less of them become sep- 

 arated in the cutting, and in every batch there are many free eggs. 

 This lack of uniformity in the composition of each lot of eggs is a source 

 of great annoyance in handling them, the free eggs floating up more 

 readily than the bunches and tending to escape through the outlet pipe, 

 but it is not detrimental to the success of the work. In preparing the 

 eggs, they were transferred as rapidly as detached to the hatching-jars, 

 previously filled with water, the eggs of each lobster being placed in a 

 separate jar, as there is more or less variation in the specific gravity of 

 the eggs of different individuals. 



As soon as each jar had received its allotment, the cap with its tubes 

 was fastened on, and a connection made with the salt water supply pipe. 

 The specific gravity of the eggs was not determined, but they require a 

 relatively strong current of water to raise them above the bottom, the 

 average amount allowed to pass through the jars having been nearly 

 a gallon a minute for each. The flow was so regulated as to give the 



*Bull. U. S. Fish Commission, iii, pp. 183-192, 1883. 



