Fishery Board Jor Scotland. 

 Incubation of Herring Ova — continued. 



* Water supply stopped for some time during the day. 



Results. 



The Lhicooled Spnv-n on Gravel. 



This spawn was not very clean. 



During incubation, the spawn was fully exposed to daj'light, but 

 not to direct sunlight. The eggs detached from the gravel vai-ied in 

 size from 1-32 to To mm. in diameter. Eggs which had been stuck 

 to the gravel, and which had been forcibly detached, had lost a patch 

 of the outer layer of the zona. This did not appear to exercise any ill 

 effect. No crystals were observed in this lot of spawn. 



The first larva appeared on the 19th- day, and larvae were 

 obtained almost daily up to the 29th day. On the latter date a few 

 of the eggs still contained embryos. 



Spnicn Incahated in the Galvanized Tin. 



This lot of spawn was treated with water similar to that supplied 

 to the uncooled gravel spawn up till the time when the larvae began 

 to appear, viz., on the 20th day. Thereafter the water was cooled, 

 and the incubation-period was, in consequence, extended for an 

 additional 21 days. The larvte hatched out daily from the 20th to 

 the 41st day. The results in this case were very satisfactory. 



The retardation consisted in keeping the developed embryos in the 

 egg after they were ready to hatch. The result was that many of the 

 larvae, when they hatched, had alreadj^ consumed a large portion of 

 the yolk. On the 40th day three had only a trace of yolk left (fig. 6). 

 although a fourth had still a fairly large ball of yolk unabsorbed. 

 A normally hatched larva may be 8 nnn. in length : a post-larva 

 measured 7"5 or 8 mm. The eggs did not seem to have suffered from 

 the cooling. 



