228 



Part III. — Fifteenth Annual Report 



for the nine stations. At this temperature the whiting's period of incuba- 

 tion is 6i days, a very much shortened period, which would probably 

 necessitate the deposition of the eggs nearer in-shore than before. 



We thus see that the conditions of spawning of the whiting, and pro- 

 bably of the poor-cod, may be largely accounted for on physical grounds, 

 though we cannot speak with certainty as to which particular feature 

 1 causes ' the others. We may start with the small size of the egg, which 

 causes a shorter period of incubation, and so suppose that this has enabled 

 the whiting to lay its eggs further inshore, and thus to escape the dangers 

 of the outer stations ; and this, again, enables the whiting to reproduce 

 itself with a lower fecundity than the cod. In a similar manner we may 

 argue the same sequence from the fact that the whiting breeds later in the 

 year than the cod or haddock, and the small size of the eggs is an adapta- 

 tion to still further assist in the approach shorewards. 



We simply have a number of organic factors — such as fecundity, size of 

 eggs, time of spawning, duration of spawning period, etc. — which, on the 

 principles of variation, must be held to have been alterable in the past, 

 and a number of physical factors ; and we can clearly see that the former 

 series has been adapted to the latter, and that the more complete adapta- 

 tion is measured by the less fecundity. 



Thus, as regards (1) the spawning-areas of the whiting, we may say 

 that they extend at least from the outer stations well up the Firth of 

 Forth. (2) The spawning-season must, from the evidence of the pelagic 

 eggs, be from the third week of February to about the middle of July T , 

 allowing a few days prior to the 22nd for the incubatory period of the 

 eggs occurring on that date. The spawning appears to take place slightly 

 earlier in the outer than in the inner stations. (3) The direction taken 

 appears to be similar to that of the cod in the earlier part of the year 

 during the prevalent east winds, when the eggs spawned in the outer 

 stations are probably drifted up the Firth. 



During the latter part of May, and the month of June, the eggs, laid 

 further up the Firth, seem, in the light of present knowledge, to be 

 drifted hither and thither in a more or less indefinite direction, with the 

 slight and changeable winds, for the short period of incubation. 



TABLE IV. — EGGS OF PLAICE. 

 Firth of Forth. 



Feb. 



8, 1895. 



Station VIII., 



. 2. 



! ! 



12, „ 



„ IX., . . . 



. 3. 



>> 



19, 1891. 



„ IX., . . . 



. Numerous. 



J, 



21, 1993. 



6 miles E. of May Island, 



. 1. 



> , 



21, 1894. 



Station VIII., 



. 16, 





21, „ 



„ IX., . . . 



. 3. 





22, „ 



,, v., . 



. 1. 



» > 



22, 1890. 



Cross-section I., 



. Eggs of. 





1893. 





. 5400. 



Mar. 



6, 1894. 



Station VI., . 



. 4 (ready to hatch). 



>> 



6, 1895. 



„ VIII., . . 



. 15. 



> » 



14, 1892. 



„ VII., . . 



. 1 (advanced). 





16, 1894. 



Largo Bay, . 



. 9. 



»» 



16, 1892. 



Station VIII., 



. 99 (early). 



»» 



16, „ 



„ IX., . . . 



. 1542 (early). 



; 5 



18, 1890. 



„ VIII., . . 



. Eggs of. 





19, 1891. 



„ v., , . . 





>> 



20, 1895. 



„ v., . . . 



. 4. 



>» 



20, „ 



„ VI., . . . 





>» 



21, 1890. 



Cross-section III., . 



. Eggs of. 



5 > 



23, 1891. 



Station VI., . 



. A few. 



, > 



29, 1894. 



„ VI., . . . 



. 12. 





30, 1891. 



„ II., • . • 



• Eggs of. 



