GENERAL BIOLOGY 



729 



Propagation 



During autumn and the last months of the year thermal 

 conditions alter greatly in boreal waters, high temperatures 

 retreating from the surface down to 200 or 300 metres (see 

 Fig. 509). At the same time the sexual organs develop in most 

 boreal food fishes : the cod family, the herrings, the tiat-fishes 

 and others, and during the three or four first months of the 



year they spawn. Most 

 of these edible fishes 

 possess large ovaries 

 containing enormous 

 numbers of eggs, the 

 cod, for instance, having 

 apparently on the aver- 

 age no less than five 

 million eggs. 



Late in the 'sixties of Develop- 

 last century, G. O. Sars ZT^T' 

 commenced his investi- 

 gations on the famous 

 cod fisheries in the 

 Lofoten Islands. He 

 found that the eggs of 

 the cod were pelagic, 

 floating in the surface 

 layers of the sea, and 

 he carefully studied the 

 development of these 

 eggs, making a number 

 of excellent drawings, 

 which I regret to say 

 have never been pub- 

 lished. These original 

 drawings foreshadow much of the knowledge gained in recent 

 years on the early development of the cod, and I consider it 

 interesting to reproduce some of them illustrating certain 

 stages. The characters distinguishing these stages are just 

 as law-bound as those of the adult individuals. One stage 

 (see Fig. 520) is characterised by dark transverse bars of 

 black pigment, which subsequently dissolve into fine longi- 

 tudinal bands, following the dorsal and ventral side of the 

 body, a fine stripe running along the lateral line. Later on the 



O. Saks. 



