432 Simon Henry Gage 



simple magnifier, are, in most cases, sufficient to make the 

 diagnosis quite certain. In perfectly fresh specimens the 

 spermary is semi-translucent and has a watery appearance, 

 "while the ovary is much more opaque owing to the food yolk 

 in the ova. In hardened specimens this difference is lost, 

 however, so that the determination must be made by compar- 

 ing the size of the gonads, and the relative size of the ova and 

 the sperm mother-cells. The ovary is always larger at the same 

 stage of development than the spermary, and usually the ova 

 are larger than the sperm mother-cells (PI, VII, fig. 28, 30). 

 If one has but a single specimen or is not accustomed to deter- 

 mine the sexes, the safest way is to make a histological ex- 

 amination. 



In plate I, it is .seen that the proportions of the sexes are 

 markedly different, apart from the greater slenderness of the 

 female. It was hoped that by a careful comparison of certain 

 definite and easily determined proportions some guide might 

 be found by which the sexes could be distinguished at all 

 seasons and independently of the transient sexual characters 

 at the spawning season. Careful measurements were made of 

 specimens that had been subjected to the same treatment, in 

 fixing and hardening so that the variations due to different 

 reagents should not complicate the problem. Except for the 

 lake lampreys taken in the breeding season where the sexes 

 could be distinguished easily, each specimen measured was 

 sufficiently dissected to determine with absolute certainty the 

 sex. The results of the measurements in all the different 

 forms studied, adult and larval, are given in the following 

 table : 



