OUR INLAND FISHERIES. 29 



to the incubation of the ova ; and he had further 

 adopted this plan because he had known of failures 

 resulting from the use of boxes, and, as he appeared 

 to suppose, in a great measure from the absence of 

 these gases. I have, however, known the boxes to 

 succeed so often both with trout and salmon that I 

 am inclined to think there was probably some other 

 solution to the mystery, and perhaps the following 

 may be the reason : When the ova is lying in the 

 gravel it is often attacked by predacious insects, 

 which prey upon it unceasingly ; and the great aim of 

 the pisciculturist is to keep vermin of all kinds from 

 the ova. Now, if the gravel with which the boxes are 

 loaded is taken from the bed of a stream without 

 being either boiled or undergoing some other process 

 to destroy the animal and vegetable life existing 

 among it, it is impossible to prevent insects from 

 being placed in the box with it, as their eggs and 

 larva are mixed with and laid in the gravel itself. 

 When the gravel is transferred to the boxes these 

 eggs and larva in the course of time are hatched 

 and immediately commence preying on the ova. Mr. 

 Ffennel, the Commissioner of the Irish Fisheries, 

 found this a very considerable source of damage 

 to the stock of spawn which was deposited in 

 the experimental boxes at the Custom-house in 



