more dark, yellow, or brownish yellow, because of the development of the blood vessel system, 

 giving the ovaries a darker color. The ovocytes are visible with the naked eye. The wei^t of the 

 roe is 1 to 5, on an average 3% of the body weight. When the ovaries are opened, the ovigerous 

 lamellae are visible. 



Histologically, the ovary in stage II is distinguished by the following criteria; the bulk of 

 the ovary consists of single -layered follicles. Ovocytes in the juvenile phase are also present, 

 but in small numbers only. Along the edge of the ovigerous lamellae, towards the cavity of the 

 ovary, germinal tissue and ovocytes in the youngest phases are found. 



Ovocytes are developed at the same time in the various parts of the ovary. This is proved 

 by cross sections made from the cranial, median, and caudal parts of the ovary. 



The juvenile stage (I) usually passes into stage II in June, more rarely in July. Ovaries in 

 stage II can be found all the year. It is therefore assumed that in immature herring the ovary may 

 remain in stage II during several months, or even years. 



According to our observations the ovaries of mature herring do not remain very long In 

 stage II, but rapidly pass into stage III. The transition is probably completed during 2-2 1/2 months. 

 In mature herring, ovaries in stage II are observed from the end of April to the middle of July. 

 Stage II may be called the critical stage, as it is followed by a rapid development of the ovaries. 



Stage in. The ovary has increased considerably, occupying approximately two -thirds of the 

 body cavity. The ovary reaches more than two times the height of stage II. Small, round eggs are 

 easily visible with the naked eye, and among them there are still smaller ovocytes, of an irregular, 

 polygon shape. These ovocytes belong to the phase with follicle tissue in one layer, which consti- 

 tute the majority in ovaries in stage II. 



The blood circulatory system is well developed. The capillaries start from a main (feeding) 

 artery as small bundles of blood vessels, ending on the lower side of the ovary. The weight of the 

 roe varies from 3 to 11%, averaging 6% of the body weight. 



The bulk of the ovary is composed of ovocytes at the beginning of formation of yolk . In 

 addition are found young ovocytes, characteristic of stage II, but as to volume they play an insigni- 

 ficant part. In spent herring, empty follicles may be seen at the beginning of stage III (Figure 6). 



Herring in stage III may be found from June to March, with a maximum in August -September 

 in the southern part of the Barents Sea . The transition from stage III to stage IV is gradual . 

 (Figures 7-8). 



Stage IV (See Figure 1, b). The ovaries occupy most of the body cavity. Blood vessels are 

 well developed. The eggs are of an irregular, polygon shape, close together. If the ovisac is torn, 

 the eggs run out, attaining a rounded shape . The membrane of the ovary is very thin and easily 

 torn. The roe has a yellow-red color. The weight varies from 5 to 15%, averagely 9.6% of the 

 body weight . 



In histological respect, stage IV is characterized by ovocytes filled with yolk. Some young 

 ovocytes are also present, inclusive of the single -layered follicles. Ovocytes with incipient forma- 

 tion of yolk are lacking . 



Herring in stage IV occur from November to April, mainly in the western part of the Barents 

 Sea, and in September along the west coast of Spitsbergen. Single males and females in stage IV 



217 



