170 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Angora doe rabbit which had been fertilized by an Angora buck thirty-two 
hours previously : the ova were, at the time, divided into four segments. 
They were immediately transferred into the upper end of the fallopian 
tube of a Belgian hare doe rabbit which had been fertilized three hours 
before by a buck of her own breed. When the Belgian doe gave birth 
she produced six young, four of which were like herself and her mate, 
and two of which were undoubted Angoras. So far as this single expe- 
riment goes it does not favour the view that a uterine foster-mother has 
any effect on her foster-children, or that the presence and development of 
foreign ova in the uterus of a mother affects the offspring of the mother 
born at the same time. 
Maturation of the Ova of Elasmobranchs.* — Prof. N. Kastschenko 
has investigated the process of maturation in the ova of Pristiurus 
melanostomus, Torpedo ocellata , and Scyllium canicula. One polar body 
is formed by karyokinesis, while the ova are still in the ovary ; a second 
may be formed subsequently, perhaps at the time of fertilization. No 
extrusion of portions of the germinal vesicle was observed, but there is 
probably some absorption of nuclear material by the yolk. 
Early Stages in Development of Elasmobranchs.t — Prof. A. 
Schneider, who has made a study of the early stages of the develop- 
ment of Elasmobranchs, reports that the tissue of the embryo consists 
of protoplasm with nuclei ; the caudal portion consists of mesoderm and 
ectoderm. In the mesoderm the protoplasm becomes collected around 
the nuclei, and the cell-territories give off processes and form a con- 
nected stellate tissue, In the ectoderm the protoplasm remains conti- 
nuous ; that layer is connected with the mesoderm by stellate tissue. 
The mesoderm gives rise to the dorsal medulla and brain as well as 
to the primitive vertebrae and lateral plates; in the anterior region 
the mesoderm is formed from the middle line of the outer layer, and 
the ectoderm appears at the sides. The primitive vertebrae are from 
the first connected by the motor-nerves with the dorsal medulla ; they 
and the lateral plates are at first connected, but afterwards become 
separated. The connective tissue and the muscles are developed from 
the lateral plates and primitive vertebras, the latter giving rise to the 
longitudinal muscles, and the foimer to the enteric and cardiac muscu- 
lature, the fin-muscles, the musculature of the gills and jaws, and to the 
vessels. 
Yolk-sac of Young Toad-fish, i — Prof. J. A. Ryder has studied the 
functions and histology of the yolk-sac of Batrachus tau. Unlike other 
fish-larvae, the young do not escape from the egg-membrane immediately 
after its rupture, but continue to adhere to it by a discoidal area, and 
are thus indirectly attached to foreign bodies. The cellular membrane 
which covers the lower pole of the yolk-sac is much thickened as com- 
pared with the rest of the outer wall of the yolk. The thickening is 
due to the peripheral ends of the cells of the epidermis being prolonged 
in the form of a homogeneous and almost vitreous-looking material. 
The whole of the free surface of the epidermis covering the yolk-sac is 
* Zeitschr. f. Wiss. Zool., 1. (1890) pp. 428-42 (1 pi.). 
t Zool. Bcitr. (Schneider), ii. (1890) pp. 251-66 (1 pi.). 
X Proc. Acad. Nat. Sci. Philadelphia, 1890, pp. 407-8. 
