238 ARTIFICIAL SPAWNING-TEENCHES. 



trench, but carefully mixed with gravel all over its 

 bottom, and then covered in with the gravel that 

 has been excavated in fomiing the breeding- 

 furrow. The trench and its covering must be on 

 the slightly inclined-plane principle. The gravel 

 with which the trench is covered in must not be 

 pressed down, except very slightly, in order not 

 to prevent the free percolation of the water, which 

 must have full ingress and egress to and from the 

 spot where the seed lies deposited. The action 

 and contact of moving water are essentially ne- 

 cessary to perfect this strange incubating process. 

 Without them ova will be non-productive, for 

 placed in gravel at the bottom of still, or slug- 

 gishly running water, they will putrify, or, to use 

 a generally known expression, they will be 

 " addled." 



For the purpose of making experiments, such 

 as watching the alterations that take place in the 

 ova during their progress towards expulsion of 

 the foetus, small wire baskets may be used. In 

 them spawn mixed with gravel is to be placed, 

 and they are to be put into the trenches of the 

 ponds. They are to be taken out from time to 

 time to ascertain the condition of the ova, some 

 of which can be extracted and preserved for the 

 information of students in natural history. The 



