[23] SCIENTIFIC EXAMINATION OF THE GERMAN SEAS. 547 



The anal fin of the sprat has 19 rays, and has a much longer line of 

 origin than the axial fin of the herring, which has only 17 rays. 



The pectoral fin of the herring has 17, and that of the sprat only 16 

 rays. 



The lower edge of the body of the sprat, in the direction from 

 head to tail, is much sharper to the touch than that of the herring, 

 because the ventral carinated scales of the sprat are much larger, 

 and have more projecting points than those of the herring (Fig. 

 III). From the head to the ventral fins the herring has 31 ventral 

 scales, and the sprat only 22. 



6. — The larval form of the flat-fish. 



As very young flat-fish are comparatively little known, we give a 

 picture of one caught in the Bay of Kiel. Like other fish it has one 

 eye on the right side and the other on the left (Fig. XV) ; 

 has the same color on both sides, and possesses a small 

 swimming-bladder, which is wanting in fully-grown flat- 

 fish. These small flat-fish are found swimming in a per- 

 pendicular position near the surface of the water, where a young flat-fish, 

 they can easily be caught with fine nets. SfftoonE! 



* One eye lies on the 



7. — Something concerning the food of fish. *$& '» n ? ^ e °i h f r 



on the leit side ol the 



The North Sea and Baltic can furnish large numbers hea(1, 

 of food-fish, because they are inhabited by enormous numbers of other 

 marine animals. The following kinds of marine animals compose the 

 greater portion of the food of fish : crustaceans, worms, snails, mussels, 

 and echinoderms. As most of these animals live at the bottom of the 

 sea, the fish will generally seek their food there. 



Herrings, sprats, and mackerel often find large quantities of small 

 crustaceans near the surface of the water. For the young fish which 

 have just left their eggs small microscopic animals, which can scarcely be 

 seen with the naked eye, are of the highest importance. At the very 

 time when the fish leave their eggs, the sea is full of larvae of crusta- 

 ceans, worms, snails, mussels, echinoderms, &c, so that the fish receive 

 a number of small animals with the water which at every breath they 

 inhale through their gills. Young fish when kept in aquaria generally 

 die very soon, because they do not get the food which they need, namely, 

 the larvae of the above-mentioned small marine animals. These animals 

 on which the fish feed live partly on other living or dead animals. The 

 last sources of their food, however, are aquatic plants and those particles 

 of organic matter which the rivers carry into the sea. 



During the autumn and winter months large masses of sea- weeds and 

 algae are torn out by the waves, lose the air which during life had kept 

 them floating, and sink to the bottom. Here they gradually decompose, 

 and finally form the principal component part of the dark mud from 

 which innumerable mussels and worms derive their food. 



