52 
AN EARLY HUMAN OVUM 
more than a day or two after the cessation of development. A number 
of otherwise valuable young ova have therefore been omitted, namely 
those of Alilfeld, Beigel and Lowm, Breuss, van Heukelom, Hitschmann 
and Lindenthal, Hoffmeier, Keibel (1890), Kollmann, Leopold (1906), 
Marchand, Rauscher, v. Spee (1905), Stolper, and Wharton Jones. The 
ovum No. 11 of Mall is also omitted as being pathological. There remain 
eleven recorded ova which meet our requirements, namely those of Peters’, 
Jung, Merttens, Beneke, v. Spee (v. H.), Leopold (No. 1), Reichert, Rossi 
Doria, Eternod, Frassi, and v. Spee (Gfle). The data regarding these eleven 
cases will now be briefly summarised and tabulated. 
For purposes of comparison in the histories and table, the age of the 
present ovum is taken as 13-14 days. In assessing the relative age of 
other young ova, the total size of the ovum, the size of the blastocyst, 
and where it is known the size and state of development of the embryo 
are all taken into account. It is probable that ova vary slightly in the 
rate of development of the embryo, and still more in the rate of growth 
of the trophoblast. Considerable variation in the rate of development is 
known to occur in certain of the lower mammals; for example, Keibel 
found in the pig differences which he regarded as equal to from 24 to 48 
hours’ growth, at such an early date as the 14th day of pregnancy. The 
computations must therefore be regarded as merely approximate; but as 
the total period considered is only 20 days, and the difference between the 
youngest and the oldest only 7 days, they may be regarded as fairly 
correct. 
SUMMARY OF DATA REGARDING SELECTED OVA. 
I.—Ovum of Peters. 
Dimensions — external, about 24 x 1‘8 mm.; blastocyst, internal, 
l’6x '8x ‘9 mm.; embryo, T9 mm. The specimen was obtained at 
sectio a few hours after death. The fixation is very good, and the 
details of its structure and imbedding have been very well worked 
out. The patient who had borne one child menstruated for the last time 
on 1st September, 1895. Towards the end of September, besides other 
