24 
The Embryology of Patella. 
supra-oesophageal ganglion, or wbether it arises from a thickening of 
the apical plate or from a combination of both I am unable to say. 
A paired tkickening of the ectoderm constituting the anterior wall 
of the foot appears at this time, which I am inclined to believe 
gives rise to the pedal ganglion. 
Explanation of Plates. 
an. c. anal cells. 
a. p. apical plate. 
a. anus. 
b. blastopore. 
en. endoderm. 
In. intest ine. 
f. foot. 
m. I. micropyle. 
m. c. mesodermic chords. 
m. s. mesoderm. 
pr. m. primitive mesoderm cells. 
m. n. mesenteron. 
o. e. Oesophagus. 
p. g. pole globules. 
r. radula. 
s. c. Segmentation cavity. 
st. stomodaeum. 
sh. g. shell gland. 
sh. shell. 
V. velum. 
I. s. lateral swellings. 
Plate I. 
Fig. 1. Chorion. Fig. 1 a. Optical section of the chorion still more highly 
magnified. 
Fig. 2. Ovum just after its removal from the ovary. 
Fig. 3. Ovum about ten minutes after its removal from ovaries, showing 
amoeboid arms. 
Fig. 4. Ovnm 1 / 8 hour old, showing two pole globules surrounded by the 
refractive particles in the cavity of the micropyle. 
Fig. 5. Ovum with large depression lined with finely granulär protoplasm 
from which a single pole globule rises. 
Fig. 6. Ovnm 3 / 4 hour old showing the two differentiated pole globules. 
Fig. 7. Fertilized ova during its first division into two spheres. 
Fig. 8. Similar ovum with two equal Segmentation spheres. 
Fig. 9. Ovum with two unequal Segmentation spheres. 
Fig. 10. Ovum with three Segmentation spheres, seen from the animal pole. 
Fig. 11. Ovum with four Segmentation spheres. 
Fig. 12. Ovum with five Segmentation spheres. 
^ig. 13. Ovum with six Segmentation spheres. 
Fig. 14. Ovum with eight Segmentation spheres. 
Fig. 15. Ovum in blastosphere stage seen from the vegetative pole as an 
opaque object, showing the four endoderm cells en 1 . en 2 . en 2 . en 4 . 
Fig. 16. Section of an ovum in the blastophere stage, passing through the endo¬ 
derm cells en 1 . en 2 , and the laterally placed endo-mesoderm cells en. m l . and en. in 2 . 
Fig. 17. Section through an embryo which has just hatched, (about 10 hours) 
showing the two equatorial bands of cilia V 1 . V' 2 . and the cilia upon the apical pole 
a. p. also the two large endoderm cells en 1 . en 2 . 
Fig. 18. Section through an embryo of about 14 hours showing the lengthened 
and enlarged endoderm cells en 1 . en 2 . en 2 . 
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