THE AETIFICIAL INCUBATION OF OVA. 45 



it. This is always useful, as it breaks up the stream 

 and scatters and aerates the water. If, however, 

 the volume be stUl so great that notwithstanding 

 this it still drives the ova about, then there is too 

 much stream and it must be reduced. By watching 

 this it will soon be seen what is the correct eodreme 

 volume of water to supply to ova, and with that 

 extreme volume I hold that a dozen trays of the size 

 stated,^ or half a dozen of double the size, are quite as 

 many as can be safely placed under one stream of 

 water. I do not, of course, mean to say that under 

 favourahU circumstances more may not be employed, 

 but taking all reasonable chances into considera- 

 tion, I think that number ample ; and if it be re- 

 quired to hatch more ova, I would establish another 

 range of trays and another stream rather than drive 

 such a stream through a siagle and more extended 

 line as might be harmful to the ova The French, 

 however, who perhaps are subject at Huningue to a 

 higher temperature in the early spring months than 

 we are, do not allow the same jet of water to perco- 

 late through more than four trays usually ; occasion- 

 ally six or seven are used, but this is exceptional. 

 They do not, however, employ so strong a stream as 



1 This will give an available stream of some thirty-four feet in 

 length, while it occupies a space of about ten feet by two. 



