MARCH: GERM CELLS OF CORYMORPHA. 257 



III. — SUMMARY AND CONCLUSIONS. 



1. The medusa bud begins development as an out-pushing 

 of the wall of the peduncle, usually near the base of the older 

 medusae. 



2. The "glockenkern" arises as a mass of ectodermal cells 

 pushed into a cavity at the apex of the bud, formed by the 

 separation of the ectoderm and entoderm. 



3. The "glockenkern" cell mass separates into two cup- 

 shaped layers, one going to form the inner lining of the um- 

 brella, the other, containing germ cells, going to form the 

 ectoderm of the manubrium. 



4. As these two layers of the "glockenkern" cell mass push 

 back the entoderm, the manubrium becomes separated from 

 the outer capsule (umbrella) of the bud. 



5. The manubrium breaks through the outer capsule, leav- 

 ing the umbrella free. 



6. Primitive germ cells, identified by certain definite char- 

 acters, are found scattered among the ectodermal cells of the 

 peduncle, most frequently near the base of older medusa?. 



7. The presence of germ cells in the entoderm only in the 

 region of developing buds, indicates the early migration of 

 some germ cells from ectoderm to entoderm at that point. 



8. The path of migration taken by the germ cells is from 

 ectoderm to entoderm at the base of developing buds, then 

 among the entoderm cells and into the "glockenkern" at the 

 apex of the bud. The entrance of the germ cells into the 

 "glockenkern" does not take place until after the latter is well 

 formed. 



9. The number of primitive germ cells entering into the 

 formation of a single medusa is fairly constant, varying from 

 17 to 32 in all the medusae counted. 



10. Multiplication of germ cells and sexual differentiation 

 does not occur until a late stage of development. 



