— 5 — APPENDIX B: HEINCKB 



We must confess that the investigations of the Biological Station up to the present in no 

 wise fulfil, and indeed could not fulfil, this demand for numerous and continuous observations. 



We have made our observations, partly by means of the research-steamer "Poseidon", 

 partly with the vessels of the Biological Station, in the neighbourhood of Heligoland and 

 in the shallow waters ("Wattenmeer") and estuaries of the German coast, from the island 

 of ßöm in the north to Borkum in the west. It is only for the neighbourhood of Heli- 

 goland, however, that we have gained continuous series of observations of moderate com- 

 prehensiveness. This was not possible on the cruises with the Poseidon. From October 

 1902, when the voyages began, up to the present (beginning of November, 1904), it has 

 been at our disposal altogether 122 days, and of these, 100 at most were working days at 

 sea. In addition, we utilised the quarterly cruises of the Poseidon to make tow-nettings 

 for fish-eggs at its stations, and occasionally also some hauls for the larger fishes. All 

 these cruises, however, were not sufficient to make a satisfactory number or continuous 

 series of observations; above all, it was unfortunately not possible to fish for the eggs, 

 larvae and youngest fully-formed stages of the fishes, at a larger number of places within 

 the extended spawning grounds of our most important food-fishes, nor at sufficiently varied 

 periods during the long duration of the spawning time. 



The following account of our results shows everywhere these gaps in the observations. 

 They are the consequence of the manifold difficulties, which always arise at the beginnings 

 of so extensive a work and can only be overcome gradually. 



The second demand, contained in the aim of our labours, requires that 

 every single observation is to be of the greatest exactness possible, and 

 that the facts are to be learnt as they are in reality. This demand for exact 

 and certain observations is even more important than that of numerous observations. Its 

 importance becomes clear at once, when we picture the difficulties which all observations 

 still meet with at sea, simply on account of the sea, and consequently, the great danger 

 there is of drawing hasty, wide reaching conclusions from imperfect, unsuccessful obser- 

 vations. Some examples will illustrate this point. It may be desired to ascertain the 

 occurrence or absence at a certain place in the North Sea of the pelagic eggs and larvae 

 of a food-fish, e. g. plaice; granted that the eggs and larvae of this species are so well 

 known that they can be distinguished from those of all other species with certainty. Long 

 experience in this field has taught us that a certain observation can only be gained in 

 such a case, when hauls are made after H ens en' s example with good egg-nets from the 

 bottom to the surface, and not merely horizontally, but above aU vertically. As we cannot 

 fish well with one net everywhere and for all purposes, we must constantly employ several 

 well-tried instruments one after the other, to obtain a trustworthy observation (we use 3 

 to 4 different kinds). The employment of a net in only one way — e.g. the hori- 

 zontal surface net — will in all cases bring an uncertain, in many cases quite 

 a false result. No eggs and larvae at all may be caught, for example, though they are 

 present in reality in quantities. 



The difficulties are quite similar if we wish to determine the occurrence and distri- 

 bution of the fry of our food-fishes, after they have given up the larval stage or better 

 called, the purely planktonic life, and have either changed to a complete bottom habitat or 

 have reached such a size and capability of free movement, that they can no longer be 

 counted with the plankton, helplessly subject to the movement of the water, even though 



