54 



Part III. — Twenty-seventh Annual Report 



The Stage of Development of the Reproductive Organs. 



During the examination of the samples it was noted that the male and 

 female herrings are similar in size. If, for example, a sample of herrings 

 contains females having very small reproductive organs, it is extremely 

 probable that with them there will be males of a similar length showing 

 testes in a corresponding stage of development. A similar relation is 

 found among herrings having reproductive organs in other conditions. It 

 is thus possible to analyse a sample of fishes by the condition of the 

 females, since it can be inferred that there will be a series of male fishes 

 corresponding to them. It is easier to gauge the stage of development of 

 the ovary than that of the testis, because the diameter of the egg gives a 

 ready indication of the nearness or otherwise of the spawning period. 



The reproductive organs have been classified in three ways: — (1) By 

 weight, (2) by their greatest breadth, and (3) in the case of the ovary by 

 the diameter of the eggs. So far as the first two methods are concerned, 

 the data only give a relative indication of the stage of development, since 

 along with these factors it is necessary to consider the size of the fish. 

 Thus a small fish may have its reproductive organ practically ripe, when 

 the organ may be very small in comparison to the ripe ovary of a larger 

 fish. Similarly, the weight of the pair of ovaries or testes cannot be treated 

 absolutely. The breadth of the organ is affected by the amount of com- 

 pression to which it is subjected by the other abdominal organs. In the 

 tables for each month the breadth of the ovary and testis have been taken 

 together and arranged at each centimetre of length of the fish. The 

 weights of the ovaries and testes have also been combined. Alongside are 

 given the sizes of the eggs which were measured. In this way a picture is 

 afforded of conditions of development which occur in herrings of definite 

 lengths. The picture is that afforded by the present investigation, and 

 does not exclude other conditions which were not observed, but which may 

 very well occur. 



A herring which has a large reproductive organ is known as a " Full " 

 herring. The full herring is recognised before dissection, since the large 

 roe or milt fills up the abdomen and gives it a firm, resistent feel. In 

 contrast to this condition, a herring which has a small reproductive organ 

 has a " slack" abdomen. The fat in the immature. herring sometimes fills 

 up a compact, clean abdomen and gives it rigidity. In the tables I have 

 restricted the term " Full " to herrings in which the roes contained eggs 

 measuring 1*0 mm. and upwards in diameter. Males which had testes 

 20 mm. in breadth and over were labelled " Fulls," Small herrings were, 

 however, full when their reproductive organs were less than 20 mm. in 

 breadth. The following cases occurred in February. A male, 17 cm. in 

 length, was full, although the testes was only 10 mm. wide. Two full 

 males, 18 cm. in length, had testes 12 and 14 mm. in breadth ; two at 19 

 cm. had testes 14 and 19 mm. broad ; three at 20 cm. had testes 13 and 

 17 mm. broad ; while one at 21 cm. had testes 18 mm. wide. A female, 

 19 cm. long had eggs 1*0 mm. in an ovary 13 mm. broad, while another of 

 the same length had eggs 1*1 mm. in diameter in an ovary 15 mm. wide. 

 Two females, 20 cm. in length, had ovaries 12 and 13 mm. broad, contain- 

 ing eggs 1*0 mm. in diameter, while two that measured 21 cm. in length had 

 eggs 1*1 mm. in diameter, in ovaries 16 and 17 mm. broad. 



The males are often a little in advance of the females in the develop- 

 ment of the reproductive organs. Thus males are sometimes found 

 apparently ripe, while the accompanying females have not reached that 

 condition. It is not at present clear how long a time may elapse after 

 the fish arrives at a full condition before spawning takes place. 



The appearance of the reproductive organs has been discussed under 

 each month. It is not necessary to recapitulate what has been already 



