H. i\ Williamson 1)9 



tory. the death-iate was often large: in some cases all the eggs of a 

 batch succumbed without hatching. There are various factors which 

 one can suppose will or may injuriously aflect the ova. and it is necessary 

 to eliminate them as far as possible. 



So far as the water was concerned the only precaution which was 

 taken was against mud. etc. in suspension: the water was filtered 

 through sand. Since ova develoj) in the water, it was considered that a 

 suitable environment for the eggs dej)en(led simply on the quantity of 

 water supplied. When however it is desirable to reduce the quantity 

 of water employed, its ([uality, in respect to the quantities of dissolved 

 gases and of matters in solution, as well as the bacterial content, demands 

 attention. Mr Anderton considered that the water of the tropics when 

 cooled down was short of oxygen. Therefore a means of adding to the 

 air content would be necessary. The quality of the air which is bubbled 

 through is important^. There is further in this connection a certain risk 

 that may follow from the supersaturation of the water with gases. Some 

 fishes have suffered through such a condition. Gas-bells may form in 

 the tissue and cause death. I have observed a gas-bell inside the dead 

 egg of plaice which had been in water into which air had been pumped 

 in great quantity. But the bells did not occur in all the dead eggs: 

 they appeared to be an exception. 



There is, in certain places, an important difference in quality between 

 the shore-water and off-shore water. Cunningham^ reported that the 

 water from the shore at Plymouth, although constantly supplied in a 

 pure condition to the eggs in the circulation apparatus, was rapidly fatal ; 

 while in the water from the open sea, although perfectly still and un- 

 changed, the ova lived. 



In the herring eggs which were incubated in water cooled below the 

 temperature prevailing, viz. 39°-46°F., crystals were often found^. 

 The crystals were rectangular, sometimes ending in an oblique tapering 

 point. They may be fine needle-like, or fairly thick bars. They have 

 been observed on the inside of the zona, between the layers of the zona, 

 attached to the yolk or embryo; in two instances they were noticed 

 inside the gut of the living embryo. 



The cooled water was restricted in amount, and it was cooled in 

 galvanized iron pipes. I consider that these crystals resulted from 



^ Cf. Shelford and AUee, Journ. Exper. Zoology, Philadelphia, xiv, 1913. 

 - Journ. Mar. Biol. Assoc. 1889-90. 



* Cf. Williamson, H. C, "The retardation of the Development of the Ova of the 

 Herring," Fisheries Scoiland Sd. Investig. 1910, ii (1911). 



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