
No. 427.] THE EGG OF BUFO LENTIGINOSUS. 531 
states that “the formation of the primitive archenteron is 
by a process of splitting, and is the direct effect of the pri- 
mary center of growth; whilst the continuation of the cavity 
produced by an overgrowth is the direct effect of the second- 
ary center of growth.” 
That the archenteron in the egg of Bufo lentiginosus is not 
formed by a splitting between yolk cells is shown, I think, by 
a study of a series of well-preserved eggs during the early 
stages of gastrulation. 
The archenteron 
never appears *'slit- 
like" at this time. 
On the contrary, its 
walls are usually some 
distance apart and its 
inner end is invari- 
ably rounded (Figs. 
IO, 11). Occasionally 
at the stage of Fig. 
I2, never earlier, I 
have seen an irregu- 
lar cleft between the 
yolk cells at the ante- 
rior end of the arch- 
enteron which might, n MOM : 
perhaps, be con- Mabdy fier stage than Fig. Kg Mns the character of the 
sidered a forward Veil nci spes ncc atrio i dag ? 
extension of the : 
archenteron, but such a cleft is usually seen only in badly 
preserved eggs where the cells are all more or less separated, 
and therefore I have always considered that it was artificially 
produced by the method used in killing and hardening the egg. 
Jordan, Wilson, and Eycleshymer (4) among others, have 
watched the disappearance of individual surface cells under the 
dorsal lip of the blastopore in the early gastrulation stages of 
the living egg. These observations seem to me to afford con- 
clusive evidence that invagination of cells plays an important 
róle in the formation of the archenteron. 

Part of a dian secti 

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