EGGS OF ONE SPECIES VARY IN SIZE. lxix 



those, of our common char which he examined a variation in diameter 

 from 016 to 0'20 of an inch. Even in the common stickleback Ransom has 

 observed that all. the eggs of the same batch have not exactly the same 

 dimensions when ripe, and still less have those of different individual 

 parents. A similar variation in the size of the eggs corresponding to that 

 of the parent has likewise been noted from trout at Otago. 



The same phenomenon has been observed in the United States, where 

 the Fish Commissioner on the M'Cloud River in 1878 remarked that the 

 parent salmon were unusually small, their average weight being under eight 

 pounds. This small size was stated to be undoubtedly caused in whole or 

 in part by the fishing at the cannaries of the Sacramento, where the 8 in. 

 meshes of the innumerable drift nets stopped all the larger salmon, but let 

 all the small ones through. The eggs when taken proved to be at least a 

 third smaller than those of most previous years, and the average number of 

 eggs to the fish .was about 3,500, against 4,200 in the previous year. In 

 this instance the smaller salmon produced the smaller eggs, but whether' 

 the decreased number was not due to the decreased size of the spawners 

 is not evident. Livingston Stone adduces another instance, asserting that 

 American trout or char living in spring water (which means deficient food) 

 develop smaller eggs than such as reside in brooks. Or poverty in food 

 has the same effect as younger and smaller fish in diminishing the size of 

 ova. This of itself would lead one to suspect that small eggs which may 

 be caused by deficient sustenance in the parent will not produce the largest 

 fry. This difference in the size of fish eggs, which among Salmonidce 

 increase in bulk up to a certain age, must have very important bearings 

 upon their artificial breeding. For the size of the micropyle must be in a 

 certain ratio to the size of the eggs, consequently larger eggs of the same 

 species will admit larger spermatozoa than smaller ones. It has been 

 maintained by some fish culturists that very great difficulties, sometimes 

 even amounting to impossibilities, occur in crossing trout with salmon, or 

 rather fecundating the eggs of trout with the milt of the salmon. As this 

 was not found difficult at Howietoun when the eggs were taken from fish 

 that had been some years in the ponds, whose eggs were approaching in 

 size those of the salmon, it appears to me that the difficulty is merely a 

 mechanical one, due to the size of the micropyle.* This, I believe, is a com- 

 plete solution of how to obtain crosses between the salmon and the trout. 



This brings us to the consideration of whether larger eggs, the produce 

 of older or better fed fishes, will eventuate in an augmented size of the 

 offspring, irrespective of the question of changing the locality they inhabit, 

 or increasing the space or amount of water they reside in. Two sets of 



.* Mr. Arthur tells us, that in 1880, one trout at Otago yielded about thirty eggs double the size 

 of all the other ova she passed, and they hatched out just the same as the rest. 



