GERM-CELL HISTORY IN THE BROOK LAMPREY 45 



licle or peritoneal cells are rare. There is no indication that 

 follicle cells are derived from germ cells. If this were the case, 

 transitional stages should be found which might be detected by 

 •nuclei of intermediate form and structure, but such have never 

 been found. 



e. Larvae 34 to 35 mm. long. In the gonad of this stage 

 many single germ cells, as well as many cysts, occur ranging in 

 size from two cells to one hundred or over. The cysts are sur- 

 rounded, as before, with folhcular cells. In many of them the 

 germ cells are in a resting condition, but in some they are in 

 mitosis. Sometimes cell nests, identical with those of the germ 

 gland, occur in abnormal positions. One of these from the fat 

 body is shown in figure 32. Some of the germ cells at this period 

 have entered the synapsis phase, while others have transformed 

 into growing oocytes, the first visible sex-distinguishing character. 



2. Historical review and theoretical discussion. Wilhelm Miiller 

 ('75) studied the early stages of development in Petromyzon 

 fluviatilis and P. planeri. He gives an account of the repro- 

 ductive system in a larva 35 mm. long, but the earlier stages 

 were apparently not studied by him. At this stage the sexes 

 could not be distinguished. Oocytes were first observed in 

 larvae 50 mm. long, and in larvae 65 mm. long the ovary and 

 testis were fully differentiated. 



Lubosch ('03) found the first anlage of the sex gland in larvae 

 of Petromyzon planeri 18 mm. long. He found two types of 

 cells in the gland, the follicle cells and the germ cells, and he 

 believed that the peritoneum was the source from which both 

 were derived. In a slightly later stage he describes a germ 

 ridge as being formed, into which connective tissue and blood- 

 vessels descend from the region dorsal to the gonad. He ob- 

 served that peritoneal cells migrate inward to form the follicles 

 surrounding the germ cells. He found that the glands remained 

 undifferentiated until the larvae are about 4 cm. long when thf 

 ovaries could be distinguished from the male glands. 

 bk No further literature exists on this stage in the development ol 

 the germ gland in the lamprey. 



