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KANSAS UNIVERSITY SCIENCE BULLETIN. 



in the region of developing buds, is a strong indication of mi- 

 gration from ectoderm to entoderm. 



In counting the germ cells in each bud, not only the number 

 but the position of the cells has been taken into consideration 

 in order to determine the migration. Some of the larger buds 

 in stage A and all of the buds in later stages were divided into 

 three parts, proximal, central and distal, and the germ cells 

 were counted in the entoderm and ectoderm of each of these 

 regions. The average of at least two counts was taken as the 

 final number for each bud. 



Table I shows the number of germ cells in stage A medusa 

 buds. Buds 1, 2, 3 and 4 were the youngest in which germ 

 cells were counted, and were too small to divide into dif- 

 ferent regions, but the presence of a considerable number of 

 germ cells in the entoderm at this time and the presence of 

 others in the ectoderm of the peduncle at the sides of the buds 

 indicates the early migration of the germ cells toward the bud. 

 The relative number of germ cells in the different regions of 

 the older buds, 5, 6, and 7, presents a fairly good indication 

 of the path of migration followed by the germ cells. The pre- 

 dominance of germ cells in the proximal third of the ectoderm 

 and the predominance of germ cells in the central portion of 

 the entoderm seems to show the passage of such cells from 

 ectoderm to entoderm at a point somewhere within the limits 

 of these two regions. The path of migration, then, is probably 

 from ectoderm to entoderm at the base of the bud, and then 

 among the entoderm cells toward the apex. The germ cells in 

 the distal part of the ectoderm are probably abnormal in posi- 

 tion, since there are so few, and since there is no indication of 

 a continued migration in that direction. 



Allowance must be made for individual variation in the 

 matter of migration. Some medusas show an early and a 

 rapid migration of germ cells, while others show the process 



