WHICH HAVE NEVER DESCENDED TO TUE SKA. 461 



who stated, in their report for I860, as follows :— " Our opinion, from the experience of 

 the last twenty years, is, that grilse never become Salmon of any stage whatever." As 

 grilse were reared from Salmon-ova at Ilowietoun, it may well be asked in reply, if 

 such were a fact, how it is that grilse may he raised from Salmon-eggs. Russel, when 

 refuting this argument of the Tweed Commissioners, and also of Mr. Mackenzie, remarked 

 upon the difficulty of obtaining conclusive evidence after the fish has assumed its migratory 

 habits and can no longer be kept under inspection to see if the grilse becomes a Salmon. 

 But, as I have now shown, the reverse experiment has been successfully carried out 

 at Ilowietoun, and eggs of Salmon have been proved to give birth to fishes which in 

 time become smolts and then grilse. 



A difference of opinion respecting the persistent or variable size of the eggs of Salmo- 

 nidoe appears to prevail, a difference which could not exist if the authors would take tin- 

 trouble to measure them when freshly removed from the parent fish, or as lying in the 

 hatching-troughs. For these eggs do not increase in size during the process of incuba- 

 tion, although such as die become sodden, white, aud somewhat distended. Uniinpreg- 

 nated eggs do not, as a rule, take on this opaque white aspect, but remain clear 

 throughout the nesting-season, neither do they augment in size. 



I propose offering a few remarks upon whether the eggs of the Salmonidoe, of the 

 same species, are invariably of the same size, and especially if the age of the parent has 

 any connection with such differences as maybe perceived; also, if any variations in 

 the size of the eggs from a single fish are to be seen. 



Ilarmer in 1707 * gave a table showing the number of eggs which he had observed in 

 certain forms of fishes, among which the Salmonidae were not included. He remarked, 

 " From this table it appears that the size of the eggs is nearly the same in great and 

 small fishes of the same species, at the same time of the year." And these observations 

 may be found, with but little variation, in the writings of authors from that period up to 

 recent years, as perhaps in no branch of biology are assertions once made more adhered 

 to without re-investigation than in Ichthyology. Passing on to the 'Zoological Record ' 

 of 1864, p. 179, we find that Professor Malmgren, having observed that certain Salmonoids 

 in a lake in Finland were descendants of the common Salmon, whose access to the sea had 

 been cut off owing to an elevation of the land, mentioned as one of the present differences 

 that this freshwater and dwarfed breed gave smaller ova than Salmo salar. In this 

 conclusion Dr. Giinthcr did not coincide, remarking that " the last character [or size of 

 the ova] will be considered very significant by all who may have a more extended know- 

 ledge of fishes, as the size of the ova is not only invariably the same in individuals of 

 whatever size, but, as far as our experience reaches, is even often characteristic of the 

 species of a genus." This opinion, slightly modified, Dr. Giinthcr still apparent ly held in 

 1880, for he asserted t that " the ova of Tcleostean fishes are extremely variable in size, 

 quite independently of the size of the parent species. The ova of large and small 

 individuals of the same species, of course, do not differ in size."' 



* Transactions of the Royal Society, " On the Fecundity of Fishes." 



+ • Introduction to the Study of Fishes,' p. 159. 



