► The Retardation of the Development of the Ova of the Herrinq. 7 



Diatoms were noticed at different times on the egg^. some of 

 which became somewhat dirty externally. They were, however, 

 parth' sheltered from the light b}^ being enclosed within the 

 partially-closed tin. They did not, therefore, become so dirty wnth 

 diatomaceous growth as the other lots of eggs. 



Crystals, in some cases in great quantity, were observed in certain 

 eggs. The majority showed none. The crystals were attached to the 

 zona, sometimes in rosette-form, or even inside the embryo. They 

 were observed in one of the trunk canals, apparently the gut (fig. 3). 

 In the embryo, a large cori^uscle plugged the heart with each pulsation, 

 and then receded again (fig. 9 J. Next day the corpuscle remained 

 clear of the heart. Crystals were observed in the gut of another 

 embryo, the heart of which had no plug. One lively embryo had a 

 huge quantity of crystals attached to the inside of the zona. 



Cooled Spawn. 



The gravel spawn examined nine days after spawning seemed to be 

 in a pretty good condition, but some dead eggs were to be seen. On 

 the 11th day, the spawn on the glass plates looked well, except where 

 the eggs were in a thick mass. In such places dead eggs were 

 observed. Some of them had no doubt been killed by the pressure of 

 adjacent eggs. Certain eggs were of especially large diameter. 

 Three that contained embryos showed no crystals, but in certain of 

 them a granular matter \\as sticking on the embryo — an unhealthy 

 sign. An egg, 1'75 in diameter, had an unhealth}^ looking embryo. 

 Two eggs measured 1'3 and 1"35 mm. in diameter. Both contained 

 cr3-stals. In one the crystals were large and few in number ; in the 

 other they were small and fairly numerous. 



By the 22nd day a copious growth of diatoms was noticed on the 

 eggs. The thickl3--covered plates did not look so well as those that 

 had a sparse coating of eggs. Larvae began to appear on the 29th 

 day. On the 42nd day a considei-able C|uantity of dead eggs was 

 observed. INIany ajopeared to the naked eye of a milky tinge. That 

 probably indicates that they had died recently. The milln^ appear- 

 ance is due to the perivitelline fluid turning opaque. Some of the 

 ova were yellow-coloured from the coating of diatoms. 



On the 51st day, ripe eggs, containing live embryos, were quite 

 yellowish. A good proportion of the eggs of one of the good plates 

 seemed to have hatched. 



I examined some eggs that had died recently. In one I could 

 detect no movement of the embryo. I dissected it out of the egg 

 capsule. The heart was found to be beating slowly. The embryo 

 seemed to be perfect. It was, I think, dying from suffocation, due to 

 the mat of diatoms that covered the zona. The larvae which were 

 obtained on each day from the 29th to the 38tli day were prematurely 

 hatched. They were very small, viz.. 4'5-6mm. long. The head was 

 markedly bent downwards, i.e., miich more than in the older larvge. 

 The postlarval body is shorter than normal. Succeeding batches 

 graduallj' improved in size. On the 38th day 94 were obtained: 

 Compared with a larva which had consumed nearly all its yolk, they 

 were shorter and had the head more flexed. They were pretty liveh^ 

 Two measured 6 and 7'5mm. in length respectively. Thereafter the 



