OF MONOTREMATA AND MARSUPIALIA. 
469 
From 1875 to 1883 Dr. George Bennett’s son (7,8) collected material for Sir R. 
Owen in Queensland. In 1880 Sir R. Owen (49) described and figured several 
ova of Echidna, taken from the uterus. In the largest of these, measuring 6 mm. in 
diameter, he observed an artificially-produced furrow, which he described as the first 
furrow of segmentation, mentioning this fission of the germ as “ additional evidence of 
the viviparity* of the Monotremes.” 
In 1882 Sir R. Owen found, lying free in the uterus of an Echidna, a large ovum 
with a “thick chorion”; vide paper published in 1884 (50). Mr. Haacke (32, 33) 
found, on the 25th of August, 1884, an egg-shell, the remains of a rotten egg, in 
the pouch of Echidna, and showed it to the Royal Society of South Australia on 
the 2nd of September. 
PART I.—THE EGG MEMBRANES, AND THE OYA UP TO THE FIRST STAGES OF 
SEGMENTATION. 
Part I. of my studies contains an account of the egg membranes, and the develop¬ 
ment of the ovum up to the first stages of segmentation, in Monotremata and 
Marsupialia. This limitation will enable me to trace the gradual replacement of 
ovarian food-yolk by uterine nutrition through the Mammalia. 
The comparison of the egg membranes yields a striking phyllogenetic interpretation 
of their development. 
The few previous investigators have failed to trace the egg membranes. 
Sir Everard Home, Mr. Hill, Sir R. Owen, and M. Yerreaux have described 
the appearance of the ovary in Monotremata. The two first observers pointed out 
the large size of the Graafian follicle, and Sir Everard (37) figured the yellow yolk 
they contained, but Sir R. Owen, in 1834 (44), still considered it probable, on a 
priori grounds, that the Monotremes had a small ovum, like other Mammalia. 
More recently Poulton (51), Beddard (2), and Goldberg (31) have observed the 
large size of the ovarian ovum, the eccentric position of the germinal vesicle, and the 
fact that the ovum completely fills the follicle during the whole period of ovarian life. 
Poulton and Guldberg have wrongly stated that the follicular epithelium remains 
always a single layer of cells. 
Beddard figures the true condition, but agrees with the other two observers, ascrib¬ 
ing the appearance of his preparation to bad preservation. Poulton came to the con¬ 
clusion that it was probable that segmentation would be found to be unequal, perhaps 
partial. Guldberg was unaware, when he wrote, that I had already described the 
partial segmentation. Guldberg and Beddard lost all trace of the vitelline membrane 
in late stages. The former says the follicular epithelium becomes changed into a 
chorion:—“es scheint, als ob die Zellen verschmolzen sind, um eine helle, schwach tingir- 
* I have added the italics, because the quotation shows the value of the old terms “ ovi-viviparous ” 
and “ viviparous.” 
