19 



no distinction between a pelagic aud a bottom-stage, aud to follow the occurrence 

 of tlie youDg in the various stages oE development we must combiue pelagic 

 investigations with iuvesti gations of the youug amongst the plant-vegetation on 

 the coasts. We have ofteu undertaken the latter kind of investigation, but it is 

 only when they contributed to solve the question of the distribution of the cod in 

 the bottom-stages that they are nientioned in this Report. For this reason I must 

 postpone furtlier description of the young of the lumpsucker. 



The greater number of specimens of Ihe young from demersal eggs wliieh 

 appear in the summer time cousists of gobies (Family: (^obiidce). We have not 

 usually distinguished between the young of the various species of Gohius in our 

 collections, nor have we always separated the young of Apliya pellucida and Cry- 

 siallogohius nilssonii from the young of Gobius. Consequently the material shows 

 but littie regarding the occurrence of these young. Further, the young of the 

 gobies like those of the lumpsucker often pass the whole of their development 

 near the bottom amongst the plant-vegetation. I have not wished tlierefore to 

 use our catches of the youug of Gohius for any description of the early life of 

 these species. For a similar reason I have lefrained from mentioning the other 

 young forms from demersal eggs occurring in summer, namely: of the sticklebacks 

 (Gasterosteus acideatus and pimgitius), tifteenspined stickleback (Spinachia vidgaris), 

 garfish {Belone acus), and pipe-fish (Syngnathns sp. and Nerophis sp.). They are 

 not dealt with in the descriptious of the species, as they often pass the whole of 

 their earlj' hfe amongst the plant- vegetation. 



Tlie bottom-stages of young flslies. 



During the development of the youug fish great changes take place in 

 their auatomical structure and pigmentation. It is thus said that the larvæ 

 imdcrgo tnefamorpJiosis, and by completély mefamorphosed* young fish is meant the 

 young which resemble the adult tish in regard to body-form, development and 

 number of rays in fins, etc. The metamorphosis begins in the pelagic stage, but 

 is usually continued after the close of this period. In the present Report, in 

 which I deal specially with the conditions of distribution of the j'ouug, I have 

 not paid so much attention to the degree of metamorphosis as to the mode of 

 life of the young, whether in iutermediate layers of water or at the bottom. 



The majority of young fish after a longer or shorter pelagic existence 

 approach the bottom, on which or near to which they pass the rest of their life, 

 but in the transition to the bottom-stage a separation occurs between the young 

 of the diiierent species which have hitherto lived together in iutermediate water- 

 layers under essentially the same outer conditions. Some species seek the bottom 

 in shallow water, others in deep, some prefer ground covered with vegetation 

 others the uncovered ground. 



* In talking of metamorphosed young of flat-fisli in the special part, I mean tlie stages 

 of these fish with the transformation of the eye so far advanced that both eyes are on the same 

 side of the head. The term "transition stages'' I use for the stages of development which inter- 

 vene between the symmetricai and the metamorphosed stages. 



