ARTIFICIAL HATCHING OF SPAWN. 49 



running shallow water, by being exposed in the trays 

 to its action, became warmer and warmer, as it tra- 

 velled from tray to tray, until there was a difference 

 of something like 2^- between the top or first tray 

 and the bottom or last one. This difference in the 

 temperature worked out very singularly in the hatch- 

 ing of the ova. With the first large batch of spawn 

 got from Hampshire, three of the upper trays were 

 supplied, these were alternate trays, with another tray 

 intervening thus the first tray supplied with this ova 

 was No. 1 tray, and the last one, No. 5 tray. There 

 was a difference of rather more than 1 between the 

 temperature of the water in the "No. 1 tray and the 

 No. 5 tray ; and this simple difference of 1 made 

 several days difference in the period of hatching. 

 The lower tray, began hatching first ; then, after two 

 or three days, the next above ; and finally, after a 

 further similar interval, the top one (No. 1). The 

 temperature of the water in the boxes in the meadows 

 was, throughout, several degrees higher than that 

 used in the greenhouse. 



When first the eggs were placed in the troughs in 

 the greenhouse, they were of a delicate pale pink 

 colour. In a few days, as there was no filtra- 

 tion, a dark brown sediment settled on them. This 

 sediment gradually assumed a spongy confervoid 



E 



