220 



Fart III. — Fifteenth Annual Feport 



In a general comparison of the spawning areas negative results may be 

 said to be of value ; thus, if, e.g., in the area of the Moray Firth, the eggs 

 of a certain species are not found to occur, the inference is that the species 

 does not spawn in that district ; for the reasons above cited, this inference 

 must be applied very cautiously in the comparison of stations in one area, 

 because the distance between the stations falls within the limits of the 

 1 pelagic drift' of the young forms. 



Thus we can first go over the data with respect to the four areas — Firth 

 of Forth, St Andrews Bay, Moray Firth, and the Clyde district — and 

 thereby institute (1) a comparison, firstly, between the stations within each 

 area ; and (2) a comparison between each area. 



2. The Determination of the Spawning Season of each Species. — The sea- 

 son of spawning may be fairly accurately determined by the occurrence of 

 eggs over a certain period, for, although in this case the strictly accurate 

 spawning-period is that represented by the occurrence of freshly-spawned 

 eggs, yet the eggs found at the latter end of the season, and tending to 

 lengthen the apparent spawning-period by the time taken in reaching such 

 an advanced stage, develop rapidly at this season, and can only add to the 

 spawning-period an error of a few days, more or less. 



The results obtained by study of the pelagic eggs can in this case also 

 be checked by means of direct experiment. Thus, the occurrence of 

 spawning-adults may be noted and compared with that of the eggs, in 

 the same manner as in the case of the determination of the spawning- 

 areas. 



In this section the questions to be determined are free from the dis- 

 turbing elements of drift-currents which enter so largely into the first 

 section, for we have no reason to believe that drifting eggs develop more 

 rapidly than those floating more or less slowly, except in so far as a 

 change to water of a different temperature would alter the rate of develop- 

 ment, and this would only have the effect of shortening or lengthening by 

 a very little the error of a few days at the end of the season mentioned 

 above. 



Under this section we can first determine the spawning-season of each 

 species in each of the three areas under consideration, and compare the 

 three results ; and, secondly, we can compound the results, and thereby 

 obtain a general spawning-season for the whole coast for each species. 



In the third section there is 1 the Determination of the Direction taken by, 

 and subsequent Fate of, the Fggs after Spawning' — In the former two 

 sections there are more or less statical determinations, the place of depo- 

 sition and the time of deposition, without reference to the further develop- 

 ment, but under this section we have to consider the dynamic con- 

 ditions in place and time of the eggs and embryos. The former of 

 these, the rate at which, and direction in which, the eggs travel is deter- 

 mined by the rate and direction of the surface drift ; and the latter, by 

 the bulk of the egg (as a constant for each species), and by the surface- 

 temperature. 



The solution of the problems here under discussion requires a complete 

 knowledge of a number of factors which we have scarcely commenced to 

 investigate. 



The drift-bottle experiments of Dr Fulton may, if carefully persevered 

 in, eventually give us a very good idea of the direction of the pelagic 

 drift-currents, but they do not always admit of sufficient accuracy to 

 give us definite knowledge regarding the rate of drift, mainly because we 

 cannot always be sure of the bottles being returned as soon as drifted 

 ashore. 



In certain cases, the study of pelagic eggs may give us the rate and 



