90 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
perhaps partial digestion, of the nucleus takes place as the ova leave 
the ovary, or as they pass through the uppermost part of the oviduct. 
We await further details. 
The Formation of the Zona Pellucida.* * * § — Prof. G. Paladino refers to 
what G. Retzius recently f maintained in regard to the connections 
between follicular cells and the ovarian ovum, and cites some passages 
from a work of his own t published in 1887, in which he described the 
intercellular protoplasmic bridges between the ovarian ovum of the rabbit 
and the surrounding follicular cells. The result of this nutritive 
connection is a reticular layer around the ovum. It is thus, namely 
from the follicular cells, that the zona pellucida arises, and its variable 
appearance, its presence or absence, are readily explained. It is an 
accessory stratum of no constancy or intrinsic importance. 
Foetal Membranes of Chelonia.§ — Dr. K. Mitsukuri has investigated 
the foetal membranes in Clemmys japonica and Trionyx japonicus. Among 
the interesting discoveries which he has made, he has discovered that 
the extra-embryonic cavities of the two halves of the amnion are never 
united with one another over the dorsal region of the embryo. A 
connection between the amnion and the serous envelope separates them 
to the very end of development and may be called the sero-amniotic 
connection. As may be supposed it causes great peculiarities in the 
foetal membranes, in later stages. The anterior and lateral folds which, 
starting from the head, have gradually extended backwards over the 
whole embryo, do not stop at the posterior end of the embryo but 
continue to grow backwards ; there is thus produced a tube which 
extends backwards from the posterior end of the embryo and is almost 
as long as the embryo itself; it connects the amniotic sac with the 
exterior. It is possible that its function is to convey nutritious matter 
from the white yolk into the amniotic cavity. 
At one spot a small mass of white persists for a long time ; it seems 
to undergo some change in its chemical composition for it becomes much 
denser and is sticky. The membranes are often slightly indented to 
receive this mass, and into it a low thick process of the membranes is 
sent ; the cells of the outer layer of the serous envelope in this process 
are peculiarly modified, and there can be no doubt that they absorb 
albuminous particles from the white. This seems to be a very primitive 
condition of the structure described by Duval as the placenta in Birds. 
Formation of the Notochord in the Human Embryo. || — Prof. J. 
Kollmann has been able to demonstrate the origin of the notochord 
in a human embryo 11-16 days old, consisting of 13 metameres, and 
measuring 2*5 mm. in length. He finds that it arises in the ordinary 
way as an axial differentiation of endoderm along the dorsal mid-line of 
the gut. Kollmann maintains that in the lower Vertebrates (. Amphioxus , 
Selachia, Urodela, and probably in Teleosteans and Ganoids) the noto- 
chord arises from the endoderm alone, i.e. from the “ chordal-entoblast,” 
• Anat. Anzeig.. v. (1890) pp. 254-9 (1 fig.). 
t Yerh. Anat. Ges., 1889, pp. 10-11. 
X ‘ Ulteriori ricerche sulla distiuzione e sul rinuovamento continuo del paren- 
chimo ovarico,’ Napoli, 1887, 230 pp. and 9 pis. 
§ Anat. Anzeig., v. (1890) pp. 510-9 (12 tigs.). || T. c., pp. 308-21 (3 figs.). 
