2 Normentafeln zur Entwicklungsgeschichte der Wirbelthiere. 
Under these circumstances Professor KEIBEL consented to my having the collaboration of Dr. Ewıng Tayror, 
and it is owing to his steady industry that the work is now completed. 
The observations, upon which all the tabulations and descriptions are based, have been made by 
Dr. TayLor, who has been occupied with this labour for two years, during which he has devoted all the 
time, which could be spared from his duties as Assistant in my Laboratory. My own share has been that 
of a consultant. To Dr. TayLor therefore belongs the chief credit and a large share of the responsibility 
for this publication. 
Most of the drudgery of getting together the titles for the Bibliography has also been borne by 
Dr. TayLor. We have endeavored to make the Bibliography complete as regards embryology, extensive 
as regards anatomy, but have included only the more important systematic and palaeontological papers, 
which seemed likely to be of interest to embryologists. 
Harvard Medical School, Boston, Mass., 
February 8, 1905. Charles S. Minot. 
Deseription of Embryos pietured. 
The embryos were in nearly every case fixed in ZENKER’s fluid, as noted in the separate descriptions. 
The measurements and drawings were made from the specimens preserved in 80°, alcohol, with one 
exception, the blastodermic vesicle of Fig. 1. H. E. C. stands for Harvard Embryological Collection. The 
numbers in the column marked “Designation” in the Tables are the numbers of the series in this collection. 
© Fig.ı (X 20): Surface view. Fig. 1a.(X 20). ‚Side view. Fig: 13 (X 5). 
Blastodermic vesicle of rabbit removed from uterus 6 days, 1!/, hours after coitus. Specimen was 
drawn fresh in salt solution. The vesicle is approximately spherical. On surface view there appears a small 
circular embryonic shield, more opaque than the rest of the vesicle. The thin albuminous envelope sur- 
rounding the vesicle is clearly visible. On side view, a darker zone is seen extending toward but not as 
far as, the pole of the vesicle opposite to the embryonic shield. This darker zone corresponds to the 
extension of the entodermal cells which do not completely surround the vesicle. In a vesicle closely 
resembling the one drawn, the embryonic shield was two-layered, ectoderm and entoderm, the latter forming 
a distinct layer beneath the ectoderm. 
Figs. 2 (X 20) and 14 (X 5). 
The drawing is a reproduction of another drawing made from a specimen which has since been cut. 
The blastodermic vesicle was removed from the uterus 6!/, days after coitus. ZENKER fixation. Measure, 
4.2 X 3.3 mm. The vesicle was slightly oval in form. The embryonic shield is pear-shaped. HENnsEN’s 
knot and primitive steak are distinct; the boundaries of the latter are not very sharply defined. There is 
a slightly more opaque area, extending from the region of the primitive streak a little beyond the posterior 
margin of the embryonic shield. This area corresponds to the extent of the mesoderm. The portion of the 
shield anterior to the level of HEnsen’s knot is somewhat darker, as viewed by transmitted light, than the 
portion posterior. This appearance is due to the thicker condition of the ectoderm in the former region as 
