GERM-CELL HISTORY IN THE BROOK LAMPREY 67 



seems to oppose the idea that they are individual constant bodies 

 in the same sense that the chromosomes are considered to be 

 so. It is more hkely that they play an active role in the meta- 

 bolic activities of the cell and that they may vary in number, 

 size, and shape as the activity of the cell varies. 



c. History and fate of the germ cells during the period of sex 

 differentiation. This period (table 2) includes larvae from about 

 35 mm. to about 70 mm. long. Figure 68 is a cross-section 

 through the germ gland of a larva 54 mm. long, from the middle 

 of this period. It shows many large, growing oocytes, as well as 

 many cysts. A comparison of sections from various larvae 

 shows that the oocytes are formed from germ cells which have 

 entered synapsis, either while isolated or while constituent ele- 

 ments of small cysts, usually of less than eight cells. In the 

 latter case the cysts become broken up by the penetration into 

 them of follicular cells, so that each of their contained cells, while 

 still in the synaptic phase or in the early growth phase, becomes 

 isolated within its own follicle. Thus, as shown in figure 68, 

 nearly all of the growing oocytes are sooner or later isolated cells. 

 In addition to these cells the section contains numerous large 

 cysts, and of these there are two kinds. In one kind the germ 

 cells are still indifferent, as shown by the fact that they have 

 not entered synapsis, but are dividing by typical mitosis. Such a 

 cyst containing two cells in mitosis is shown at the left of the 

 figure. In the second kind of large cyst the cells have entered 

 synapsis. Such cysts are shown to the right of the figure and are 

 recognizable by the different behavior of the chromatin. In large 

 cysts the cells which enter synapsis rarely become growing oocytes, 

 but sooner or later degenerate, until finally they and their enclos- 

 ing follicles break up and disappear. A longitudinal section of a 

 gland from a larva 59 mm. long, in which two such degenerating 

 cysts are found, is shown in figure 69. The cyst at deg.cy.2 is 

 in a later stage of degeneration than the one at deg.cy.l. A 

 detailed drawing of such a cyst from another section is given in 

 figure 65. The cells of such a cyst rarely get beyond the synize- 

 sis stage before degeneration sets in. Degeneration begins with a 

 condensation of the chromatin into solid masses, as shown at 



