ANATOMY OF LIMNOCNIDA TANGANYICA. 279 
bud to form the “ glockenkern” (g/.) or forecast! of the ecto- 
dermic lining of the subumbrella cavity. As the ectodermic 
invagination sinks deeper into the interior of the bud, its cells 
acquire definite walls and arrange themselves in a single layer 
round a central cup-shaped space. The mouth of this space now 
closes up, and finally the entire “ glockenkern” becomes covered 
over by an overgrowth of ectoderm, and its cells become marked 
off from the cells of the peripheral ectoderm (figs. 11 and 
lla, gl.). At this stage the “ glockenkern” is a hollow 
sphere of ectoderm, one cell thick, enclosing a hollow cavity, 
which, as has been shown above, is really a portion of the ex- 
terior which has been enclosed during the growth of the bud. 
Meanwhile, owing to the invagination of such a comparatively 
~ bulky mass of ectoderm, the endoderm thins out so much as to 
be reduced to a single cup-shaped layer of cells enveloping the 
central “ glockenkern.” 
A second ingrowth of ectoderm now occurs. The ectoderm 
cells at the apex of the bud become less vacuolated and undergo 
changes similar to those which the cells of the “ glockenkern” 
passed through, and grow down as a solid plug of cells into the 
apex of the “glockenkern.” Before this stage is reached the 
“ slockenkern ” was more or less spheroidal or egg-shaped, but 
the effect of the second ingrowth of ectoderm is to push one 
wall of the “ glockenkern” into the other, with the consequent 
result that the “ glockenkern”’ becomes a two-layered cup sur- 
rounding a plug of ectoderm cells. A further result is that the 
lumen of the “ glockenkern ”—the future subumbrella cavity 
—becomes considerably reduced in size and may even, in some 
cases, disappear altogether (figs. 12 and 12a). In the latter 
case it always reappears at a subsequent stage. The outer 
wall of this cup-shaped “ glockenkern”’ will ultimately form 
the ectoderm of the subumbrella, while the inpushed wall will 
1 T have used this word as the English equivalent of the word “ Anlage,” 
which has presented so much difficulty to translators. The use of the terms 
“rudiment ” or “fundament ” (Prof. E. L. Mark) is not to be recommended 
in this sense. For some considerable time past the members of Professor 
Lankester’s “Seminar” at Oxford have been accustomed to use the term 
forecast” with the significance of ‘* Anlage,” 
