GERM-CELL HISTORY IN THE BROOK LAMPREY 111 



tain hormones, secreted during the development of one or the 

 other form of sex cell, and which inhibits the development of the 

 other. When one set of sex cells is exhausted, the action of the 

 hormones ceases and the other set of cells begins to develop. 



In dioecious animals and plants the two forces do not exert 

 themselves in the same individual except as the result of unusual 

 conditions. In the free-martin, for example, the female potency 

 is in the lead from the beginning of development; but by the action 

 of hormones circulating through the body of the embryo, the 

 male factor asserts itself so that the female factor is partially 

 suppressed, even to the extent "that a gonad with a primary 

 female determination may form a structure which is morpho- 

 logically a testis" (Lillie, '17, p. 468). When the spider-crab, 

 Inachus, is infected with the parasite Sacculina, the males, para- 

 sitically castrated, may show every degree of modification 

 toward the female state, even to the appearance of ova in the 

 remaining part of the testis. The females, however, are not 

 transformed toward the male condition, and the conclusion is 

 drawn by Geoffrey Smith that the male is heterozygous for sex 

 and the female homozygous. Such a conclusion is hardly war- 

 ranted, for the parasite does not seem to act simply by arresting 

 the action of one sex potency, but by also elaborating certain 

 materials which are favorable to female development. That 

 this is so may be surmised from the fact that when immature 

 females are infected, the effect is ''to force them to assume pre- 

 maturely adult female characteristics" (Smith, '10). There is 

 no reason, therefore, why a female, when infected, should be 

 transformed toward the male side. 



In pigeons, sex seems to be a matter of metabolic difference, 

 and a disturbance of the metabolic level may be brought about by 

 hybridization as well as bj^ overwork in reproduction so that a 

 sex reversal is effected. In this case Riddle thinks he has dem- 

 onstrated "that germs normalltj female-producing, have, under 

 experiment, been made to develop males; and that germs which 

 were prospectively male-producing have been made to form 

 female adults" (Riddle '16, p. 410). In the case of the gypsy- 

 moth, hybridization again seems to disturb the sex metabolism 



JOURNAL OF MORPHOLOGY, VOL. 35, NO. 1 



