POLYEMBRYONIC DEVELOPMENT IN TATUSIA 565 
taken from the fallopian tubes show a development almost as far 
advanced as that of some vesicles taken from the proximal parts 
of the horizontal grooves. 
Taking all the facts into consideration, I estimate the ‘period of 
quiescence’ to last about three weeks; that is from about the mid= 
dle of October to the third or fourth of November. There are ex- 
ceptions to this, but not sufficient in numbers to modify the gen- 
eral conclusions. Of the thirty-four free blastocysts obtained in 
1911 and 1912, twenty-eight of them were secured within this 
period. 
There is another line of evidence which more or less supports the 
above conclusion. [refer to the condition of the corpus luteum. 
In all the females from which the free blastocysts were taken the 
corpus has attained approximately its maximum size. Unless we 
attribute a phenomenal rate of growth to the corpus, it is neces- 
sary to assume that quite a long period has elapsed since ovulation 
took place, in order to account for its large size. The short fal- 
lopian tube of the armadillo precludes the suggestion that the egg 
has spent a great while in traversing this passage, so that we must 
conclude that any arrested development in the egg takes place 
after it enters the uterine cavity. 
So far as the writer is aware, the only other mammal in which a 
similar quiescent period in the development of the blastocyst oc- 
curs is the deer. According to Assheton (’98) Bischoff (’54) states 
that in thisanimal the embryo, upon reaching the so-called morula 
stage, enters upon a ‘period of quiescence,’ and remains unaltered 
for some weeks. 
It is scarcely correct, however, to state that the blastocyst of 
the armadillos, during the entire period of quiescence, is in a state 
of arrested development, because it undergoes certain progressive 
changes. So far as one can tell from a study of sections, no mi- 
totic divisions occur, but the vesicle increases in size, due to the 
accumulation of fluid within its cavity, accompanied by the atten- 
uation of the trophoblastic cells. Furthermore, the differentia- 
tion of the ectoderm and entoderm from the inner cell-mass is com- 
pleted while the blastocyst lies free within the uterine cavity. 
