

WHICH HAVE NEVER DESCENDED TO THE SEA. 403 



The foregoing are only some out of the many measurements which I have made, but they 

 tend to show very conclusively that the size of the eggs iu Salmonoids increases with the 

 age and probably the condition of the parents ; thus the ova of grilse are inferior in size 

 to those of the Salmon. And in large Trout as in the older Lochlevens there is an 

 augmentation in the thickness of the shell *, a rather important question to the fish- 

 culturist, because such shells require a strong embryo to readily hatch, which is 

 obtained by giving an increased supply of water during their " eyed " period. Whether 

 it was accidental or otherwise, still the Trout eggs obtained latest in the season were of 

 rather larger size than such as had been taken in the earlier months. 



Next we come to the consideration of whether any difference is perceptible in the eggs 

 of two parents of the same age that have been kept under identical conditions. Amoug 

 the young Salmon reared at Howietoun from eggs obtained from the same parents, and 

 reared in the same pond, some taken on December 1st, and again on the 13th, 18S4, 

 averaged - 22 of an inch ; some from similar fish on December 9th averaged O20 of an inch, 

 while others taken the same day were 022 of an inch. The same phenomenon has been 

 observed among the Lochleven Trout, wherein, although the diameter of the eggs of fish 

 at 8 years of age was generally 024 of an inch, in some it was 022, in a few 0'21, and 

 in three or four O20 ; whilst in six-year-olds it has been observed to vary from 0"1S to 0*19 

 of an inch. That such variations might theoretically be anticipated most of us must 

 admit, for whatever causes deficiency of nutrition might occasion diminution in the size 

 of the ova. Also the size of the parent ought possibly to be taken into account, for 

 disease, crowding them when young, and other causes may dwarf these fishes, and such 

 would probably give comparatively small eggs. 



Can we detect any variation in the size of the eggs given by a single fish ? I have 

 already adduced an instance of this among the Lochleven Trout. In November 1884, I 

 placed 80 unimpregnated eggs of one of these fish in a tube of water, wherein they were 

 kept for a week, the water being changed daily. At the end of this period I measured 

 each ovum, and found 75 were - 25 of an inch in diameter, three were 020 of an inch, 

 one was 0-175 of an inch, and one 0'15 of an inch. Looking through the hatching- 

 troughs at Howietoun it appeared that from 4 to 5 per cent, of the eggs are less than the 

 normal size of the remaining 95 or 96 per cent. 



I must here refer to the grounds on which I believe that offspring raised from the large 

 eggs are superior to such as are reared from the smaller ones. Two batches of Lochleven 

 Trout were spawned on November 2nd, 1882, the parents of one lot having been hatched 

 in 1875, and of the other in 1876 ; these ova were similarly treated and the young came 

 out during January and February 1883. At Craigend are two ponds which have been 

 constructed for the reception of young Salruonidae, each being 100 feet long and about 

 25 wide : one is nearly on a level with the other, and the same stream passes through 

 both. Into these two ponds the two lots of fry were turned, those from the older (1875) or 



* The micropyle in the Salmon's eggs has nine pits or depressions around the opening, whereas there are none in 

 the ova of Trout, including Sea-Trout. 



SECOND SERIES. — ZOOLOGY, VOL. II. 69 



