478 
MR. W. H. CALDWELL ON THE EMBRYOLOGY 
Wharton Jones (71) was the first to notice the addition of the albuminous coating 
in the Fallopian tube. He considered that this coating gave rise to the chorion. 
Barry (61) has given a most elaborate account of the origin of the chorion. His 
results are strikingly similar to what I have described in Pliascolarctos; and it is not 
too much to admit that, if no one had thrown doubts on Barry’s work, I should 
have had no difficulty in comparing the membranes of Pliascolarctos with those of 
Monotremata and Marsupialia. Dr. Barry (62) stated that the chorion arose from 
“cells” (not the cells of the tunica granulosa, but “cells” appearing in the Fallopian 
tube) on the outside of the zona pellucida ; that this chorion imbibed fluid, and 
separated from the zona pellucida ; that after the fluid was absorbed the zona pellu¬ 
cida again lay close to the chorion; and that the chorion gave rise to villi. Dr. 
Barry’s experiment of crushing the fresh ovum, and finding that its contents, passing 
outside the zona pellucida, were still contained in his chorion, is striking evidence in 
favour of the existence of such a membrane, although, unfortunately, no recent 
observers have described any trace of it. 
Table showing the Homologies of the Egg Membranes in Mammalia. 
« 
Monotremata. Marsupialia. Placentalia. 
Layer of coagulated fluid in = Coagulum . . . = Coagulum. . . . = Vitelline membrane of 
bardened mature ova. Van Beneden. 
Vitelline membrane = Vitelline membrane. = Vitelline membrane = Zona radiata = inner 
layer of mature ova¬ 
rium, zona pellucida. 
Pro-albumen secreted = Pro-albumen . . . = Pro-albumen. . . = Outer granular layer 
by follicular epi- of zona pellucida 
tbelium. (Wal deter). 
Shell membrane = Shell membrane = Shell membrane = Villous? “non-cellular” 
formed outside al- with villi which without villi P chorion (Bischoff). 
bumen in Fallopian become “ cones.” 
tube and uterus. 
Comparison of the Egg Membranes of Mammalia with those of other Vertebrata. 
Very numerous statements have been made concerning the egg membranes of both 
Ichthyopsida and Sauropsida (68 and 69). I shall not attempt to compare all the 
membranes that have been described, because it is both certain that many are either 
transitory arrangements of the peripheral protoplasm of the egg or the product of 
hardening reagents, and also probable that some are optical illusions. 
That a pro-albumen such as I have described in Monotremata has not been recog¬ 
nised in most Vertebrata is due possibly to the shortness of the period of its formation. 
Cunningham (67), however, has recently shown that such a structure exists in 
Myxine, but he assumed that it gave rise directly to the shell, and consequently could 
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