APPENDIX E: HEINCKE _ 24 — 



depth. A spawning centre obviously occurred here. Verj' large quantities of eggs 

 were also found, however, to the north and west of this, in the deeper waters between the 

 Dogger Banli and the Dutch-German coast. The quantities decreased further to the north 

 beyond Horns Reef, occurred only sparingly at the Skaw and were quite absent in the 

 hauls over the deeper parts of the Skager Rak. On the Dogger Bank itself they were 

 somewhat scarce, but again became more numerous on its northern edge and then, in the 

 direction towards the Great Fisher Bank, they gradually decreased. They also occurred 

 afterwards at the Great Fisher Bank to the amount of 25 per square meter of surface. 

 Older larval stages were not taken in any quantity worth mentioning. 



In May also, we still found very large quantities of dab eggs, though not to such 

 an extent as in March. We obtained the largest quantities of 50 to 70 eggs per square 

 meter on our Stations I (40 m. line, N.W. from Heligoland), II (south-east corner of the 

 Dogger Bank), XV (southern Horns Reef) and V (northern portion of the Great Fisher 

 Bank) ; at the last place, the spawning had without doubt begun later than in the southern 

 North Sea; (even in August, considerable quantities of dab eggs were taken on the Great 

 Fisher Bank and some single eggs also, at the end of September). We took somewhat 

 smaller quantities, but still worth mentioning, of 20 to 30 eggs per square meter on 

 Stations 111 and IV (south and west of the Great Fisher Bank) and XIV (south of the 

 Jutland Bank). On the other hand, but insignificant quantities were taken at all the 

 Stations VI to XII lying within the region of the Skager Rak. 



Dab eggs were taken at Heligoland from the end of January to the middle of July, 

 in greatest quantities from March to May. Larvœ were also taken with the eggs, as a 

 rule often in very considerable numbers and always in young stages of development, before 

 the formation of the fin-rays. These stages, however, are mostly no longer quite young 

 but are so far advanced, that their separation from plaice larvae of similar size, as above 

 mentioned, presents considerable difficulties. 



In July, further advanced larvae of the dab were taken in no small numbers at 

 numerous points of the region under survey. They were mostly in the earlier and later 

 stages of the formation of the fin- rays. 



Thus, all stages of the metamorphosis were observed, partly from the planktonic speci- 

 mens, partly from those taken on the bottom, and at the same time a very striking 

 fact was displayed. It appears namely, that the dab is distinct from all other flat- 

 fishes in that the stages, where the left eye is already on the ridge of the head, are never 

 taken in the plankton. The dab thus changes over to the bottom-life at an 

 earlier stage of metamorphosis than its nearest allies, the plaice and 

 flounder, in which all the metamorphosing stages are always planktonic. 

 Specimens with the eye on the ridge, usually 15 to 17 mm. long, represent already the 

 earliest bottom-stages. In these, the body-pigment, which develops greatly during the first 

 period on the bottom, is seen in active process of formation. 



The earliest bottom-stages and the fully-developed 0-group of the dab 

 have been taken by us, from June on, at very numerous places of the entire region under 

 survey, in the eastern and northern North Sea, from the mouths of the Elbe and Weser as 

 far as to the 100m. line between Scotland and Norway, in depths from 1 to 100m. and 

 under the most varied conditions of salinity and temperature , from 31 to 35 per mille 

 and 6 to 13° C. Beyond the 100 m. line, they gradually became scarcer. It was remark- 



