100 Part III. — Seventeenth Annual Report 



Stage of Development of the Eggs. 



The development of the pelagic egg has been conveniently divided into 

 five stages by Hensen and Apstein.* Hensen and Apstein, in comparing 

 the eggs as to stage of development, contrast in one Table the number of 

 eggs in the first stage with the total number of eggs {p. 5Jf) ; and in a 

 second Table (p. 61) compare the eggs of the first stage to the sum of the 

 eggs in other stages. I have adopted the latter as the standard for 

 comparison, and shall reduce the relation to a ratio for the sake of 

 simplicity. They may be briefly described as follows : — 



Stage a. — From the fertilisation of the egg up to the formation of the 

 blastoderm and the germinal cavity. 



Stage p. — From the formation of the blastoderm up to the closure of 

 the blastopore. When the blastopore closes the embryo is half round the 

 yolk. 



Stage y. — From the closure of the blastopore up to the point in 

 development where the embryo is two-thirds round the yolk. 



Stage S. — From the end of Stage y. up to the point where the 

 embryo is three-quarters round the yolk. 



Stage e. — From the end of Stage 8 up to hatching. 



Figures of corresponding stages are given by Hensen and Apstein. 



Nearly half of the eggs captured in Loch Fyne during 1898 were 

 in the first stage of development (a). Of a total of 31,516 eggs, 15,000 

 belonged to Stage a ; while the other stages, ft y, S, and e, were 

 represented by the numbers 5691, 6424, 2295, and 1987 respectively. 

 The eggs in Stage a are not, on an average, more than two days old, 

 and in number they nearly equal the eggs which have reached later 

 stages of development. The proportion of a eggs to eggs in other 

 stages varies in each month, and varies also for each station. In this 

 connection attention will be restricted to the principal spawning months — 

 viz., March, April, May, and June. 



[Table. 



* Hensen and Apstein. Die Nordsee- Expedition, 1895. Kiel, 1897. 



