DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 871 
autumn when swarms of little gurnards are captured, the smallest of which are very little 
larger than those reared in the laboratory, while others are three or four times longer. 
Moreover, experience of fishes such as the salmon, in which all the ova issue nearly 
simultaneously, shows us that the growth of the young of the same fish is variable, many 
being larger than others at a given time; some, for instance, becoming smolts at the end 
of the first year, others not till the end of the second. Further, during the second year 
great disparity occasionally exists amongst the young fishes. 
When we come to survey the condition in the cod, the problem is more complex, since 
the material is less abundant and more difficult to obtain. Statements had been made 
by various authors about the life-history of the cod, but these were both vague and 
incomplete ; Prof. G. O. Sars, indeed, as already indicated (p. 153), was the first to 
produce a definite and satisfactory account of certain stages. He, however, found no 
intermediate links between the larval form of 6 mm. and the post-larval form 24 mm. in 
length, the former occurring on 28th May, the latter on 12th June, and the most recent 
remarks of RypER leave the same gap. The spawning period of the cod, therefore, would 
appear to be later in the Norwegian waters. It occurs as a rule in April in the British 
seas, though a margin must be given on both sides of this period,* and the larval cod 
abound in the surface-waters in areas frequented by the adults at the time. Towards the 
end of the same month, however, small Gadoids occur in St Andrews Bay, the least being 
about 6 mm., so that it is possible such represent a post-larval stage from early ova. 
Others again are double the length and upward, indeed there is great variety. These 
small forms are met with amongst the others throughout the summer, and generally occur 
in the mid-water net rather than in the trawl. On the 1st of June, however, the dis- 
tinctive coloration of the young cod (now 43 in. in length) is recognised, in a rudimentary 
condition, and subsequently there is no difficulty in following it. They occur in the 
trawl, and at the margin of the tidal rocks.t Now, can we assert that all these are the 
young produced from the ova of cod which spawn in April? At first one of us was 
disposed to think that those which appear in shoals off the rocks in June, and which are 
about an inch in length, were those of the previous season, since it would be dithicult to 
explain this remarkable rapidity of growth if the spawning period (viz., April) be correctly 
stated. Though the latter rests on proved observation, yet it must be borne in mind 
that the limitation of the spawning period to April is arbitrary, and it may only reach its 
culminating point then. This consideration, and the remarks formerly made as to the 
causes of variability in size, may, when coupled with great rapidity in growth, form the 
whole into one continuous series of young cod of the season. Such has been rendered 
more probable by the occurrence of the smaller forms early in April as well as subse- 
quently. Moreover, a change of area apparently takes place to some extent, since the 
mid-water net shows that these post-larval cod only appear in the Bay in April and May. 
* Vide “The Pelagic Fauna of St Andrews Bay,” Seventh Annual Report of the Fishery Board for Scotland. 
+ As shown in the Report on the Pelagic Fauna, the sizes of the pelagic young-food fishes captured in the mid-water 
net does not increase as the season advances, apparently for the reason that the large forms go downwards as they grow. 
