40 



DEPARTMENT OF TEE NATAL SERVICE 



EiiBRYOxic Development of Egg of Cod. 



This system of division is based on no other principle than that of obtaining, as 

 easily as possible, a survey of the numerical values at the different stages, these last 

 being so selected as to be distinguishable with no great difficulty when slightly 

 magnified, and without regard to ^\hether one stage may be of longer duration than 

 another. 



Apstein's tables show, for instance, that my "germinative disc" stage embraces 

 31 per cent of the total period of development in the ovum; stage 11, 46 -per cent, and 

 stage III, only 23 per cent. 



Taking the material consisting of cod eggs from the cruises of the Princess we 

 find, for all hauls made, the following figures : — 



First cruise. Second cruise. 



Stage 1 4.315 1,391 



II 799 340 



III 13 33 



Larvse 6 6 



We find then, on both cruises, an overwhelming majority of ova in the early 

 stages. How is this to be explained? Is it to be taken as entirely due to mortality or 

 destruction by some means, or do other factors here exert their influence, rendering 

 the immediate impression produced by the above incorrect? 



As we shall see, a table of this sort should be treated with the greatest caution. 

 The proportion between the different stages is not only dependent, for instance, upon 

 mortality, but also to a high degree upon the time at which the investigations were 

 made; in addition to which, we have also to consider the position of the stations 

 in relation to the spawning grounds. 



'When the investigations are carried out early in the spawning season, then 

 naturally there will be a very high percentage of newly-spawned ova, and no late 

 stages. Investigations later in the season, on the other hand, will give the opposite 

 result. 



A few rich hauls made on the exact spot where spawning takes place wi)l give 

 a different result to that obtained from hauls made out over the greater depths where 



