The culmination of the preparation of the organism for spawning corresponds with the maxi- 

 mum of the direct solar radiation. If each stage in the sexual cycle shall be carried through nor- 

 mally, certain ecological conditions are needed. Dement 'yev (16) states that during the life cycle 

 there is a reciprocal action between the internal and external factors. No cycles will arise without 

 the action of external factors. 



In addition to other factors which act as a whole, the li^t is of great importance. As a 

 result of the work of several scientists, the influence of lig^t on the living organism is now better 

 understood. The light is acting as a catalyst, influencing the hypophysis, and throu^ the hypo- 

 physis the gonads of the fish. According to Knipovich, the sunli^t which penetrates the water 

 layers, is not only a source of warmth, but may also have a chemical effect. 



In a series of experiments with living organisms, light has been shown to be important as a 

 stimulus for the development of the sexual organs. Without experiments, we may only assume 

 that during the period of maximum solar radiation the gonads of the herring receive a maximum of 

 stimulation from the sunlight, corresponding to the beginning and ending of the annual cycle (stages 

 II, III and V). 



Only by special experiments may exact data be obtained on the correlation between the de- 

 velopment of the gonads and the influence of light. The light probably plays an important part in the 

 ecology of the herring. Even if the period of intensive sunlight in the Polar Basin is very short, it 

 is evidently sufficient for a normal life cycle for the organism.s living tnere. 



The Maturity Stages and the Composition of the Blood 



In contradistinction to the warm-blooded animals, the blood of the fishes is subject to very 

 great variation in its composition. 



The ecological conditions have a great influence on the composition (59) . Puchkov measured 

 the seasonal variation in the quantity of the erythrocytes and hemoglobin in the blood of fishes . The 

 infection of fish with parasites has also a great influence on the composition of the blood (Liamin 

 (41)). 



Our investigations support the theory that in schooling fisn, especially the Murmansk her- 

 ring, the degree of infection with parasites is more or less uniform . More reliable results might 

 be obtained from samples taken in the same areas during the same periods of the year. As we still 

 do not know the normal composition of the bloodof the Murmansk herring, the figures that we have 

 are not entirely reliable for an evaluation of the biological state of the herring. It is very import- 

 ant, not only to know the absolute quantity of hemoglobin and leucocytes, but also the factors which 

 control them. 



An over-all consideration of similar problems is subject to a special investigation and is 

 not our responsibility. We will only discuss the variation in the composition of the blood of fishes 

 in relation to the maturity stages of the gonads. According to Pavlov and Krolik (57) the hemo- 

 globin and erythrocytes in the blood of fresh-water fishes increase in quantity in connection with 

 the rip»ening of the sexual products. In the species investigated, the carp, the sex of the immature 

 individuals could be determined from the quantity of hemoglobin in the blood. The authors also 

 mention the possibility of estimating the degree of maturity of the sexual products by the aid of this 

 indicator . 



Kalashnikov (31) determined the degree of maturity in sturgeon by referring to the physio- 

 logical condition of the fish. He investigated only one of the physical -chemical properties of the 



241 



