GERM-CELL HISTORY IN THE BROOK LAMPREY 89 



chromosome hypothesis does not offer a satisfactory explanation 

 of normal hermaphroditism in animals and plants. Hermaphro- 

 dites normally produce both male and female sex cells in the same 

 individual, but in most cases the two kinds of cells are not ma- 

 tured at the same time. Usually the male germ cells are rip- 

 ened first, and in such cases the species is known as protandric. 

 When the eggs are matured first, the species is known as proto- 

 genic, and when the male and female germ cells are produced at 

 the same time, the condition is known as simultaneous hermaphro- 

 ditism. The latter condition is usually found in species with 

 more or less widely separated male and female sex glands, but 

 it may also appear in species in which an ovotestis is found, as, 

 for example, in certain pulmonates. When the germ cells are 

 ripened during successive seasons of the life-cycle of the animal, 

 the condition may be called polycyclic. On the other hand, if 

 the animal produces only one kind of germ cells during the early 

 period of its life and the other kind of germ cells during the later 

 period, the condition may be termed monocyclic hermaphrodit- 

 ism. The latter condition exists in Crepidula fornicata. Orton 

 ('09) has made a study of this form and has found that the indi- 

 viduals associated in chains offer transitional series from maleness 

 to femaleness both in primary and secondary sexual characters, 

 beginning with a male in the young stage and ending with a 

 female in the older stages. Three hundred and fifty chains 

 were examined, and it was found that the individuals could be 

 arranged as follows: 1) male; 2) male with rudimentary uterus; 

 3) hermaphrodite with small uterus; 4) hermaphrodite; 5) her- 

 maphrodite with small penis; 6) female with rudimentary penis; 

 7) female. 



In monocyclic hermaphroditism it appears that with the aging 

 of the animal its metabolism becomes antagonistic to the devel- 

 opment of one or the other of the two kinds of sex cells. In the 

 case of Crepidula, the metabolism of the young animal is favor- 

 able to the development of the male sex cells, while the metabol- 

 ism of the older animal is more favorable to the development of 

 the female sex cells. In the case of polycyclic hermaphrodites, 

 when the two kinds of germ cells are ripened in close succession, 



