NATURE 



11 



THURSDAY, NOV^EMBER 22, 1SS3 



THE GERMAN FISHERIES COMMISSION 

 Vierter Bericht tier Commission zur 2uissenschaftlichen 

 Untersuchiing der deutschen Meere fiir Jnhre 1877- 

 iSSr. II. Abtheilung. (Berlin : Paul Parez, 1883 ) 

 nPHIS portion of the Fourth Report of what might 

 -l perhaps be called the German Fisheries Commis- 

 sion is a folio volume of considerable thickness, consisting 

 exclusively of three elaborate scientific memoirs, each of 

 which is stamped with the thoroughness so characteristic 

 of German work. The first, by Dr. Adolf Engler, deals 

 with the marine fungi of Kiel Bay, the second, by Dr. R. 

 Mobius and Fr. Heincke, with the fish fauna of the 

 Baltic, and the last contains an account of the properties 

 and history of the eggs of certain fishes, by Dr. von 

 Hensen. 



The second, which we shall first consider, is the 

 most important and the largest — extending to nearly 

 100 pages — and consists of an elegant and concise de- 

 scription of all the species of fish hitherto found in 

 the Baltic. As the work is founded on observations 

 extending over twenty years, made with the advantages 

 of constant residence on the Baltic shore and of control 

 over the collections in the Kiel Museum, the list is as 

 valuable as it is complete. This makes the absence of 

 some forms we should naturally have expected all the 

 more remarkable : we have especially noticed the absence 

 of Myxine, but perhaps to those better acquainted with 

 the distribution of this interesting form its absence will 

 not be a matter of surprise. 



The descriptions are preceded by an introduction which 

 explains in a very lucid manner the principal points of 

 fish organisation and their relative importance in identifi- 

 cation. This is followed by a simple classificatory cata- 

 logue of the fishes described. In this catalogue all 

 Teleostei are divided into Physostomi and Physoclisti. 

 It is satisfactory to find the great fundamental characters 

 which divide the Teleostei insisted upon, but there seems 

 no objection to retaining the criterion of the fin rays for 

 the Physoclisti, especially as this criterion brings out the 

 affinity between Gadidas and Pleuronectidas. 



The concise and elegant descriptions are supplemented 

 by a useful fin formula which makes comparison easy. 

 The food and habits of the fish are mentioned, the 

 spawning habits being especially described, and each 

 account is accompanied by a simple but extremely well 

 executed woodcut, in which all the characteristic features 

 are definitely indicated in outline. The object stated in 

 the preface, to make identification practicable to laymen, 

 has been certainly attained. 



In the account of the herring considerable space is 

 given to the discussion of the differences between the two 

 races which the labours of the Commission have shown 

 to exist in the Baltic. Perhaps before long it will be 

 ascertained whether the same differences exist between 

 the spring and autumn herring of the North Sea. 



The last portion of this memoir consists of general con- 

 siderations on the fish fauna of the Baltic. The authors 

 find that this sea may be divided into three regions, each 

 Vol. XXIX. — No. 734. 



characterise! by a distinct fish fauna, of which the 

 Western receives the greatest number of occasional 

 visitors from the North Sea. They conclude that the 

 Baltic was once in open communication with the Arctic 

 Ocean, and that some of the species offish which entered 

 at that time remain now as inhabitants of the Gulfs of 

 Bothnia and Finland. This portion of the work is 

 illustrated by an interesting map. Appended to the 

 whole is a table of the spawning periods of the fishes 

 constantly inhabiting the Bay of Kiel, and also an index 

 of the Latin names of the fishes described, and another 

 of their German, Danish, and Swedish synomyms. 



Dr. von Hensen reports at length on the researches 

 made by him during four years on the eggs of the plaice, 

 flounder, and cod. 



Agassiz described the eggs of the plaice as floating at 

 the surface, while the Swedish naturalist, Malm, affirmed 

 that they slowly and gradually sink. The first eggs that 

 Dr. Hensen obtained from a ripe female plaice gradually 

 sank. This being a question of the relation between the 

 specific gravity of the eggs and of the salt water, Hensen 

 carried out a series of investigations into the specific 

 gravity of the different eggs and their natural condition 

 when deposited by the fish. By an elaborate process of 

 measurement and calculation he arrived at the specific 

 gravity of the ripe eggs before extrusion, and ascertained 

 the limit of specific gravity and the salt percentage in the 

 water which determines whether the eggs of the cod and 

 plaice shall float or sink. He found that cod's eggs 

 floated in water which contained more than r85 per cent, 

 of salt ; and plaice eggs, when the percentage was above 

 178. These correspond to a specific gravity of 10145 

 and 10136 respectively, at 17°-^ C. He found from the 

 observations of the Commission that the water in the 

 Bay of Kiel has very often a spe:ific gravity less than 

 these. Thus there is an e.xception even to the statemen 

 that cod's eggs float. As will be seen, they always float 

 in the open ocean. It was found that the specific gravity 

 of the e^gs before extrusion was somewhat greater, and 

 their volume somewhat less than in the fertilised eggs 

 which had been in sea water, and further that the eggs 

 swell somewhat by the absorption of water without salt. 



The author next calculated, from the number of female 

 fish taken on a given fishing-ground and the average 

 number of eggs contained in each, the average number 

 of eggs in the sea corresponding to a square metre of 

 surface, and then made careful continuous nettings of the 

 eggs to find if the actual number coincided. He fished 

 the bottom, and the surface, and vertically. Eggs of the 

 plaice and flounder were frequently taken at the bottom. 

 He found the eggs pretty evenly scattered, and often ob- 

 tained them in the proportion of 30-80 per square metre 

 of surface. He then discusses what proportion of eggs 

 are likely to be destroyed by their various enemies. This 

 is the first attempt which has been made to estimate the 

 actual number of eggs of fishes hatched in a particular 

 area. The whole paper bears evidence of the most pro- 

 found and careful work. 



The memoir which stands first in the book gives an in- 

 teresting account of the areas of sea-bottom in the Bay 

 of Kiel known as "vveisser" or "todter Grund." They 

 are called " dead " by the fishermen because no fish are 

 found on them, a fact probably due to the presence of 



