jective criteria, the line between two subsequent stages cannot always be determined exactly. 

 Such difficulties will disappear to a great extent, if the macroscopical description of the gonads is 

 combined with a histological investigation. 



Figures. Ovary of Murmansk herring Nov. 12, 1938, No rdkyn Bank. Length of fish 240 

 mm., age 5+, stage IV. x 67. 



The most important of the macroscopical criteria are those which can be expressed in 

 mathematical terms, i.e., the index of maturity of the sexual products, the number of ovocytes in 

 various phases of development which can be counted in a square unit of a histological section, the 

 extent to which the ovaries occupy the body cavity, and so on. 



The use of transitional stages cannot be entirely avoided, as the scale indicates a continuous 

 development of the ovaries, with a gradual transition of the ovocytes from one phase to another. 



The ovary shown in Figure 2 can neither be referred to stage II nor stage III, but must be 

 characterized as a transitional stage between II and III, named II-III. The presence of a few ovo- 

 cytes (in the field of view) in the phase of the beginning of formation of yolk cannot justify the refer- 

 ence of this ovary to stage EI. On the other side, the great quantity of ovocytes in the single-layer- 

 ed phase, and in the juvenile phase, does not give reason to ascribe the ovary to stage II, because 

 there are at least two ovocytes at the beginning of yolk formation. 



In the further development of the ovary, ovocytes at the beginning of yolk formation, in- 

 crease in quantity, and the ovary as a whole is passing over to a typical stage IE. 



A typical stage is characterized by ovocytes in one phase or another occupying nearly the 

 whole ovary. In ovaries of the stages HI, IV, and V, ovocytes in early phases of development 

 (juvenile, or single -layered cells) are poorly represented. In other cases the ovary had to be 



220 



