230 BULLETIN OF THE BUREAU OF FISHERIES. 
the houseboat are fastened to the latter with eyebolts sliding over vertical rods 
to allow solely for up-and-down motion. Each of the four rafts contains six 
rearing cars, 10 by ro feet square and 4 feet deep, so arranged that they can be held 
down in place or raised out of the water to be cleaned (fig. 4, pl. vim). The 
rearing cars are provided with removable windows covered with 16-mesh bronze 
woven wire screens to allow for renewal of water and to prevent escape of fry. 
There are two windows about 2 feet square on the bottom and two long narrow 
ones in the middle of two opposite sides. - 
For several years previous to last summer canvas bags about the dimensions 
of these boxes and provided also with screen windows were used almost exclu- 
sively. They equaled or perhaps surpassed the boxes in point of efficiency 
when they were in perfect condition, but were less durable and were more diffi- 
cult to clean. 
The apparatus for keeping the water in motion consists of a two-bladed 
horizontally placed propeller of about 414 feet radius not unlike those sometimes 
in use over restaurant tables (fig. 3 and 4, pl. vu); the latter, in fact, suggested 
their adoption. The propeller blades are hung inside the car near the bottom and 
are made to revolve slowly—about nine revolutions per minute. The motive 
power for the propeller is furnished by a gasoline engine situated in one of the 
houses and connected with the propeller shaft by a system of steel shafting and 
mitered gears (fig. 1, 2, 3, pl. vii and vu). Each propeller can be thrown in 
and out of gear independently. 
HATCHING METHODS. 
Handling the egg lobsters—The method now used in hatching the eggs is 
simple. The old female lobsters carrying eggs about ready to hatch (fig. 9, pl. 
XI) are put directly into boxes and the paddles are set in motion. As the old lob- 
sters crawl about on the bottom of the cars, the eggs"hatch out one by one and the 
larve, caught immediately by the upward revolving current, are carried up 
and off the bottom as they are in the ocean. ‘Twenty to 30, or even 50 to 100, 
lobsters may be put in one car. When the number of old lobsters is large, we 
have found it well to replace the long propeller by a shorter one hung somewhat 
farther from the bottom so that the old lobsters will move freely over the bot- 
tom with tails extended and not crowd up into the corners. Screens placed 
over the top of the box, thereby shading them from the strong light, also help 
to prevent crowding (fig. 7, pl. x). As soon as a sufficient number of fry have 
hatched out the old lobsters are removed to another car to repeat the operation. 
The length of time required to hatch out a full complement of fry in one box 
varies, of course, according to the various conditions; that is, the number of egg 
lobsters, the condition of the eggs, the temperature of the water, etc. 
Precaution as to age of fry.—It is of great practical importance to have a 
full complement of fry hatch out as quickly as possible—within at least one day— 
so that all will be about the same age. Otherwise, when the fry moult the older 
