From September 1941 to January 1942 the author was engaged in a study of ths 

 brai-J of the skipjack at the PrJau Tropical Biological Station. During this period 

 he was also able to make some observations of the gonads of some of the skipjack 

 \vhicn were taken there. Ke had hoped to clarify the annual changes in the gonads 

 by making observations over a long period of time, but because of the short duration 

 of his stay at Palau he '-ras able to continue his observations for only three months. 

 He tinists, however, that these observations will not be entirely without value at 

 the present time vvhen all sorts of knowledge about the skipjack are so much to be 

 desired, and so, in spite of the brevity of his researches, he has decided to pre- 

 sent his observations here. He will feel amply rewarded if they may be of some use 

 as reference data for further study in this field. 



From the skipjack taken by the boats of the Nank5 Fishing Company about 10 fish 

 representing all sizes from the largest to the smallest were selected from each 

 school for study. After the J.ength end iTeight of the fish had been recorded the 

 bellies were opened and the gonads removed. The length* and weight of the gonads 

 were then determined. As will be shown below, in general the large skipjack had 

 large gonads and the small skipjack had small gonads, but it was not only in the 

 large fish that the gonads were in an advanced state of maturity. The gonads of 

 some of the large fish were not in an advanced state of ripening, while some of the 

 smaller fish had gonads which, although small, were ripe. There was no noticeable 

 correlation between the size and ripeness of the gonads. (This fact is demonstrated 

 by Figure 1,) For this reason a series of grades or degrees of ripeness was set up 

 based on criteria which could be readily determined by examination. Some of the 

 points on which these estimates were based were the number of blood vessels on the 

 surface of the gonads, the roundness and distension of the gonads, and the degree to 

 iitoich the ova had taken shape. In the case of the testes the presence or absence of 

 milt in the central lumen of the organ was one of the points on which judgments were 

 based. The selection of these criteria was not based on a critical examination of 

 the question of #iether or not they were an accurate standard, but they are thought 

 to be probably related to maturation and from the standpoint of practicality they 

 are a convenient means for distinguishing degrees of ripeness. Based on these 

 criteria four grades of maturity were established for the ovaries and three for the 

 testes. The number of grades could have been further increased by finer divisions, 

 but for observations based on the standards described above this seemed like an ap- 

 propriate number of categories. There were, of course, gonads of a degree of ma- 

 turity ^ich fell between these categories, but they were few. The limits of the 

 categories cannot be exactly defined here, but in general they were as follows: 



Females 



Grade 1, The ovaries as a whole are thin, and the blood vessels are not devel- 

 oped on the surface, which is smooth. The ova do not show as distinct 

 grains. 



Grade 2, Thicker than Grade 1, development of blood vessels perceptible on the 

 surface, which shows diagonal folds (Figure 2, lower right). 



Grade 3. Thicker than 2, folds further developed on the surface, purplish 

 stripes appear along these folds (Figure 2, lower left). 



Grade 4. Thickness further increased, surface distended, more numerous purple 

 stripes (Figure 1), 



*The lengths of the left and right gonad, may differ. In such cases only the longest 

 one was measured. 



