This item is of interest in other respects. As our knowledge of the herrings of the North 

 Atlantic is extended, and the species Clupea harengus is split into small taxonomical units, it will 

 be necessary to establish new scales of maturity, adapted to the forms present. But such an adap- 

 tion has not given satisfactory results . Earlier investigators studied the cyclic changes in the 

 gonads isolated from the corresponding changes in the organism as a whole. The ecological con- 

 ditions of the surrounding medium and their influence on the cyclic development of the gonads of 

 the fish were not taken into account. 



For the following species no special scale of maturity has as yet been worked out: lamprey, 

 skates, sharks,, salmonids, Thymallus , Osmerus, Silurus, Esox. mackerels, gobiids, Mugil , and 

 eels, (Only commercial fish have been included). For the families of herring, carps, perches, 

 codfish, flatfishes and sturgeons the scales do not satisfy the demands of the practical -scientific 

 investigations. Scales have been worked out for some fish of these families, taking into account 

 the biological peculiarities of the fish and the corresponding basic demands of the practice . These 

 scales are not free of elements of subjectivity, do not describe the characteristic features of the 

 fish in full detail, and are not always well suited for the field investigations. 



There are many scales of this kind, i.e. those of Melen for perch and carp, of Gerbil'skiy 

 for the mirror carp, of Lukin and Molchanova for the sturgeon (we have combined the macroscopic 

 description by Lukin with the microscopic one by Molchanova into one scale). 



In this way no satisfactory scales exist for most of our commercial species of fish. It is 

 therefore absolutely necessary to begin an all-round systematic investigation on the sexual cycle 

 of the most important species of fish. To work out new scales for the maturity is a very urgent 

 task. 



The scale must satisfy several demands . 



1 . The scale must describe the variations of the gonads during their development in a 

 correct way. 



2. The scale must be worked out in correlation with the biological qualities of the fish. 



3. Both macro- and microscopic data are needed for the determination of the number of 

 stages in the scale . 



4. The number of stages must be moderate. 



5. The scale must be simple and well suited for field work. 



The scale of maturity described later (page. . . .) is built upon the above-mentioned prin- 

 ciples for the description of the maturing of the ovaries. 



TABLE 8. A TABLE OF MATURITY SCALES FOR FISH. 



Species 



Criteria, on which the descriptions are based 



Author 



Herring, C. 

 harengus 



Plaice, Pleur . 

 plate ssa 



Color, elasticity of the ovaries, visibility of ovocytes 

 with the naked eye and with a magnifying glass, degree 

 of transparency of the ovary, fluidity. 



Transparency, form , color of the ovocytes , develop- 

 ment of the cavity of the ovary. 



Helncke (1898) 



Maier (1906) altered 

 and supplemented the 

 scale of Heincke . 



228 



