GERM-CELL HISTORY IN THE BROOK LAMPREY 79 



that sex was determined wholly by external factors. In the 

 lamprey it appears that the two sex potencies are almost balanced 

 and that under normal conditions it is a matter of chance which 

 sex develops, so that shght changes in the environment might 

 suffice to throw the balance in favor of one or the other sex. 

 It cannot be denied, however, that the eggs, from the time of 

 fertilization, may show a greater tendency in favor of one sex 

 than the other, as has been supposed by Witschi to be the case 

 in normally developing eggs of the frog; but this inherited tend- 

 ency may not be strong enough to prevent the formation of a 

 series of intermediate individuals with glands ranging from those 

 with no oocytes to those with no cysts. Under such conditions, it 

 is not difficult to understand how a sex reversal might take place 

 as a result of extraordinary external conditions. The more 

 equally balanced the sex potencies are, the more easily a sex 

 reversal might be effected. 



Granting that sex potencies may be inherited factors, it does 

 not seem necessary to assume that one sex is homozygous for sex 

 and the other heterozygous, as Witschi and others have assumed, 

 who felt themselves obliged to bring the phenomena of the inher- 

 itance of sex in line with those of the inheritance of mendelian 

 characters. Before entering upon this question further, it will 

 be necessary to summarize briefly the morphological evidences 

 obtained from the present study in favor of a possibility of sex 

 reversal in the lamprey. 



Following an earlier indifferent period, when no sex characters 

 are present, there is an indeterminate period in the early larval 

 life of the lamprey during which the future sex of the individual 

 cannot be determined, in spite of the fact that the sex characters 

 are present. During this indeterminate period, all of the germ 

 glands develop oocytes in greater or less number, with the 

 exception of possibly a few in which no oocytes are found. 

 At the same time many germ cells in all the glands remain in 

 an indifferent condition and are found either as individual cells 

 or in smaller or larger cysts. Since the secondary sexual char- 

 acters do not appear until later in the life of the animal, there is 

 during this period no other sex distinguishing character than 



JOURNAL OF MORPHOLOGY, VOL. 35. NO. 1 



