BIOLOGICAL OBSEEVATIONS ON THE HEREING. 635 



for the yoimg- fish could be found. They died, if not sooner, at any rate 

 after the yolk had been consumed. The growth of the fish could, there- 

 fore, not be observed in one and the same individual, but had to be esti- 

 mated aj) proximately from a scries of measurements made on different 

 fish, which only kept fresh for a short time, and then had to be replaced 

 by freshly-caught fish of the same size. 



In the spring of 1878 1 at length succeeded in raising young fish, reach- 

 ing a length of 72 millimeters, from eggs which had been used in the 

 above-mentioned second experiment. My observations confirm, as a gen- 

 eral rule, the data regarding the growth of the herring given in the report 

 of the commission. There were, however, some differences in the details 

 which will jiTStify me in giving in this place a full report of this experiment. 



As has been mentioned before, the eggs were impregnated at Cappeln, 

 on the Schlei, on the 26th of April. The second, third, and fourth day 

 after impregnation they were kept in water having a temperature of 

 only 2° C. (35.6<^ F.); the remaining time they were kept in the open 

 water of the Bay of Kiel, having a temperature of 11-12° (51.80-53.0° 

 F.). The entire season of development lasted 14-15 days. A short 

 time before the young fish escaped from the eggs the dish containing 

 the eggs was jjlaced in an oval wooden vessel, measuring 135 centime- 

 ters in length, 95 in breadth, and 77 in height, and holding about 0.7 

 cnbic meter of water. Half of this water was every day replaced by 

 fresh water from the bay, which could flow off slowly, but continuously, 

 through a sponge firmly pressed in a round opening at the bottom of 

 the vessel. This sponge served as a filter, hindering the animalcules 

 which serve as food for the larvte of the herring from escaping. During 

 the course of the summer the temperature of the water on the surface of 

 the bay increased to 25° C. (77° F.), and in the wooden vessel, which 

 was generally protected from the light and heat by a wooden lid, to 

 about 20° (08° F.). The saltness varied between 1.15<|ind 2.20 per cent. 



When within two days the greater portion of the eggs had been 

 hatched, I did not wait any longer for the remaining ones to be hatched. 

 The number of young fish was anyway very considerable. They always 

 kept together like a swarm of bees, and when the sun was allowed to 

 shine on the water they often came to the surface. 



After one to two days many of these young fish already showed a con- 

 siderable increase in length, the largest measuring 9.2 to 9.3 millimeters. 

 After three days many had lost the umbilical bag entirely and showed a 

 widely opened mouth. After five days food could be recognized in the 

 intestinal tract. In some it consisted of a fine-grained greenish mat- 

 ter, whilst in most it was composed of embryos of gasteropods and 

 bivalves of the smallest kinds of Rissoa, Uh'(e, Lacuna, TelUna, Cardium, 

 Mya, which at this season of the year fill the water of the Bay of Kiel 

 near the sliore. These embryos can easily be distinguished by thfeir 

 small shell, and swim about in the water in a very lively manner. Those 

 which were found in the intestinal tract of the larvse of the herrings had 



