604 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
to be the homologue of the centrosome (or Nebenkern) of seminal 
cells and of the centrosome of somatic cells, his remarks are of general 
interest. It arises from the nucleus of the young egg, from which it 
becomes separated as a small bud, at the moment when the egg 
leaves the epithelial or germinal layer of the ovary to continue its 
development in the ovarian follicle. The vitelline nucleus exercises 
on the protoplasm of the egg an influence analogous to that which 
the centrosome exercises on the protoplasm of ordinary cells ; it con- 
denses on its surface the surrounding vitellus, in the form of a more 
or less thick layer, the appearance and arrangement of which vary with 
the age of the egg and the species of the animal. This peripheral layer 
of the vitelline nucleus is comparable to the plasmic mass which is 
called attractive sphere in other cells. 
Another analogy which the vitelline nucleus presents to the centro- 
some is its occasional existence in a double form. The size of this 
nucleus generally increases with that of the egg, so that it equals or may 
be larger than the germinal vesicle. This growth is a true hypertrophic 
degeneration due to the superabundant nutrition of an element which 
has passed into a state of physiological inactivity. 
The vitelline nucleus does not appear to be formed in certain 
Araneids, or, if it is, it disappears early, or is so fine that it cannot be 
perceived with the means as our disposal. In other Araneids it can be 
easily observed at all periods of development of the egg and embryo. 
The theory of Boveri regarding the physiological decadence of the 
female centrosome is confirmed by the author’s observations on Spiders ; 
their vitelline nucleus may, in fact, be considered as the female centro- 
some which has become degenerate, and lost its physiological signifi- 
cance in the life of the cell. The formation of a vitelline nucleus 
deprived of its normal properties is a phenomenon which has something 
more than a mere atavistic signification ; it is a “ phylogenetic 
reminiscence.” 
As there is a homology between the vitelline nucleus and the centro- 
some it is probable that these two elements have an identical origin. 
The nuclear origin of the centrosome explains the important part which 
this element plays in the reproduction of the cell. 
Development of Liver and Pancreas.* — Herr W. Felix has studied 
the development of the liver and pancreas in the Chick and in Man. 
In the former the first sign of the liver is to be found in the depressions 
of the pharynx; the walls of the intestine form two grooves which 
extend from the head towards the tail of the embryo, and become 
gradually constricted to form two distinct canals. The more anterior 
(cephalic) canal is situated on the dorsal side of the large veins which 
go to the heart, while the posterior (caudal) canal lies on the ventral 
side of the same veins. The caudal canal (which corresponds to the 
right hepatic duct of the adult) gives off two wing-like prolongations 
which bud into the mesenchymatous tissue. The median parts of these 
prolongations are hollow, while the peripheral or terminal buds are 
solid ; as they meet the buds anastomose, and form the hepatic plexus. 
* Arch. f. Anat. u. Physiol., 1892. See Journ. de l’Anat. et de la Physiol., xxix. 
(1893) pp. 143 and 4. 
