566 _ J. T. PATTERSON 
2. Available material 
The desirability of having at one’s disposal a close series of 
early stages for a study of this kind is self-evident; but from what 
has been stated in the foregoing pages it is clear that many 
obstacles stand in the way of securing such a series. This is parti- 
cularly true with reference to the cleavage stages. In another 
season this much desired material can probably be obtained by be- 
ginning to collect at a period still earlier than that of the preceding 
year. During the season of 1912 about a dozen uteri, with attach- 
ed fallopian tubes and ovaries, taken from females in which signs 
of recent pregnancy were evident, were preserved. The study of 
some of these has led to the discovery of early blastocysts lying 
within the lumen of the fallopian tube. It is therefore highly prob- 
able that if a complete series of cleavage stages is to be had, it 
will be necessary to pursue the laborious method of making sec- 
tions of the fallopian tubes from females showing signs of recent 
fertilization. 
In this connection I should like to point out a possible source of 
error, and one that must be carefully guarded against. In sec- 
tioning the ovaries of females well started in pregnancy one occa- 
sionally finds undivided eggs in that part of the fallopian tube 
which is situated close to the ovary. Such cases are to be attrib- 
uted to ovulations that have occurred after normal ovulation and 
fertilization have taken place. The fact that the nucleus in these 
eggs may undergo division does not signify anything of unique 
importance, since it must be regarded simply as an expression of 
the same tendency to parthenogenetic development which fre- 
quently is seen in matured ova still confined Within the ovarian 
tissues of this animal. 
In table 1 is given a list of all the free blastocysts which have 
been secured during the seasons of 1911 and 1912, including the 
two taken from the fallopian tubes. The first vertical column 
gives the catalogue number of the specimen, arranged chronologi- 
cally; the second, the date at which the vesicle was taken; the 
third, the diameter of the vesicle in millimeters, measured in 70 
per cent alcohol; the fourth, the ovary, right FR or left Z, from 
