THE MARINE AQUARIUM 343 



movement, and that every now and again the impending 

 mother pays attention to these egg clusters, the claw of 

 the last leg, now on one side then on the other, being 

 called into requisition to comb out and separate any 

 too crowded mass, so as to allow full contact with the 

 ever-renewing water surface. 



In fishery stations, where fish ova are hatched on a large 

 scale for restocking depleted districts, this movement is 

 imitated by machinery false bottoms to the shallow 

 hatching tanks being made to rise and fall with slow and 

 regular action. 



In scientific laboratories, where it is required to hatch 

 and rear a few forms at a time, this is accomplished by 

 means of " plunger jars " vessels in which a pistonlike 

 arrangement is moved by clockwork, so as to slowly rise 

 and fall through the water in the vessels thus maintaining 

 constant currents. 



A simple plan which answers well is as follows : 

 Suppose it is desired to hatch some eggs of lobster these 

 can often be found on the parent in the fish markets. As 

 the eggs are maturing they show black patches the large 

 black eyes of the little lobsters that are to be. It is best 

 to secure them at this stage. 



Within a vessel of sea- water place an upright, glass jar, 

 well submerged above its rim. At a little distance from 

 the bottom of this jar, say half-an-inch, have a false 

 bottom of perforated zinc, and from a reserve tank at a 

 height of a few feet above the vessel have a rubber tube 

 terminating in a pointed glass nozzle. Let this glass nozzle 

 be passed through the perforated zinc false bottom to the 

 bottom of the jar. 



The eggs are now placed, an inch thick, or less, on the 

 perforated zinc, and the current from above allowed to run 

 through. The eggs will be gently moved, forced up, and 

 allowed to settle, with a gentle and regular movement, 



