GERM-CELL HISTORY IN THE BROOK LAMPREY 83 



less tendency toward juvenile hermaphroditism is not known, and 

 no opportunity has yet been offered for an investigation of this 

 question. 



What it is that keeps a larva with hermaphroditic tendencies 

 from developing into a functional hermaphrodite is not known. 

 It appears that when one of the sex tendencies takes the lead, 

 it prevents the development of the structures characteristic of the 

 other sex; or it may be that when one set of sex elements begins 

 to degenerate, there are removed certain influences that have 

 previously inhibited the development of the other set. Some- 

 thing similar to this is seen in most true hermaphrodites, where 

 only one set of sex cells develops at a time, so that the animal is 

 either protandrous or protogenous. In this case, too, the devel- 

 opment of one set of germ cells is antagonistic to the develop- 

 ment of the other, but a reversal always takes place when one 

 group is exhausted. This may be due to the fact that certain 

 hormones are ehminated from the germ cells which have taken the 

 lead in development, and that these are unfavorable to the develop- 

 ment of the other set. As soon as the first set of cells has been 

 eliminated, a reversal takes place and the opposite set develops. It 

 may be looked upon as alternate periods of vigor and depression 

 as far as the particular germ cells go. In bisexual animals with 

 juvenile hermaphroditic tendencies, it may be supposed that the 

 animals never recover from the state of depression relative to the 

 opposite sex. 



Reviewing the case of the lamprey, the evidence seems to 

 warrant the conclusion that sex is not irrevocably fixed at the 

 time of fertilization; that the future sex of the animal is not 

 definitely determined until the larva has reached a considerable 

 size, and that sex is not the result of any unchangeable sex quality 

 present in the egg at the time of fertilization, but is rather the 

 outcome of a balanced sex potency which results in one or the 

 other sex being formed, largely as a matter of chance under 

 normal environmental conditions. It is possible that one sex 

 potency may be stronger than the other from the beginning of 

 development, and that even the germ cells themselves at the 

 time of fertilization may be inclined in one or the other direc- 



