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 R or left L, from 



