APPENDIX. 113 



and when we consider the durability, ease with which they may be 

 handled, and the certainty with which they retain the fry, we see that 

 the boxes far surpass the bags. Furthermore, the current in the cars 

 differs greatly from that in the bags. In the latter the current is a 

 sort of an ascending spiral and is in a measure continuous in direction. 

 In the wooden boxes, because of the square corners, the current 

 "doubles on itself," as it were, in each corner. This, if not allowed 

 to be too strong, is of great advantage to the fry, often enabling a 

 weaker one to escape the pursuit of its stronger neighbor. The food 

 also tends to be scattered more widely through the box. 



The wooden rearing boxes (Plate XX) are 10 feet square and 4 

 feet deep. They are built throughout of matched spruce strengthened 

 by 2 by 3 timbers and in form are like ordinary boxes. The inside 

 corners or angles ma}' be truncated or not, just as desired, by wide 

 boards carefully fitted in. (There is perhaps a slight advantage in 

 truncating the corners but it is by no means very important.) In 

 the bottom and on two sides of the rearing boxes are windows. The 

 frames of these are made of furring (figs. 1, 2, and 3) and are covered on 

 the outside with a heavy galvanized screening (from 4 to 8 meshes to 

 the inch) designed to keep out the fish and also to protect the inside 

 screen, which is usually a bronze wire netting (16 inches to the inch) 

 and therefore quite light. This inside screening may be of various 

 materials 1 — such as wire netting of copper, bronze, or galvanized iron, 

 or may be made of perforated metal. Bronze wire is used at present 

 because it is inexpensive, and with care will last an entire season or 

 longer. Furthermore, the gauge of the wire is small and therefore 

 interferes very little with the circulation of water. 



The rearing cars are sunk into the pools of the rafts about three 

 quarters of their depth and are held down by 2 x 8 spruce planks, 

 which are notched to fit over the projecting 2x3 posts in each corner 

 of the car (Plate XX, fig. 10) and are clamped clown to the rafts by 

 iron hasps. A toothed hoisting-drum (Plate XIX) is located on the 

 4x6 uprights at each corner of the pools and enables these cars to be 

 easily raised whenever desired. 



As soon as the fry in a rearing car have reached the fourth stage, 



