72 PETER OKKELBERG 



of each of these is indicated by the dots and open circles above 

 and below the oblique line cd. The whole diagram may represent 

 ten larvae of any size between 35 mm. .and 70 mm. in length. 

 If a large number of larvae of all sizes between 35 mm. and 70 

 mm. in length were sorted according to the number of cysts and 

 oocytes present, approximately the same number of them would 

 fall within each of the vertical spaces. Those to the left of the 

 line ah would be predominantly male and those to the right pre- 

 dominantly female, as judged by the number of cysts and oocytes 

 present in the germ gland. Those on the extreme left would 

 be more strongly male and those on the extreme right more 

 strongly female than those which would fall in the groups nearer 

 the line ah. 



Although the future sex of the larvae cannot be determined 

 for a long time after oocytes have appeared in the germ gland, 

 there is apparently developed out of these indeterminate larvae 

 an approximately equal number of males and females. As 

 previously stated, it is very difficult to obtain exact data on the 

 sex ratio in the adult lamprey, since the habits of the two sexes 

 are so different; but it has been found that out of all the adults 

 collected from year to year and at various times of the day as well 

 as at various times during the breeding season, there is only a 

 slight excess of males over females, the ratio being about 118 

 males to 100 females. Many of the larvae, therefore, which bear 

 the unmistakable female character of possessing oocytes must 

 later develop into males. 



d. Literature on the period of sex differentiation in the lamprey. 

 W. Miiller ('75) found that in larvae of Petromyzon planeri 35 

 mm. long the germ cells were not yet differentiated, while in 

 larvae 50 mm. long oocytes were found. In larvae 65 mm. 

 long he found the ovary and the testis to be fully differentiated. 

 Lubosch ('03) found in the same species that sex differentiation 

 takes place at the end of the first year. The youngest identified 

 ovary was from a larva 40 mm. long. 



Lubosch was the first to call attention to the fact that hermaph- 

 roditism is of common occurrence in the larvae of lampreys. 

 He examined forty-nine germ glands from larvae of Petromyzon 



