ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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intra-embryonic endothelium ; and (&) the local origin theory, that 
mesenchyme may, in practically any region of the body, transform into 
vascular tissue. Morphological evidence favouring the local origin of 
intra-embryonic endothelium from mesenchyme has been completely 
confirmed by experiment, and the angioblast theory, in the sense 
maintained by His, no longer holds. J. A. T. 
Germ-Centres in Lymphoid Tissue. — Waro Nakahara and James 
B. Murphy ( Anat . Record , 1921, 22, 107-12, 2 figs.). The lympho- 
poietic function of the spleen and lymph-nodes is a well-known fact, 
but it is uncertain just how the production of new lymphocytes is 
brought about in these organs. Flemming first called attention to the 
frequent occurrence of mitosis in the tissue of lymphoid organs, especially 
at a certain spot in the follicle, which he called the “ germ-centre.” 
This view has been generally adopted. The authors prove it. They 
describe several kinds of lymphoid reactions in which stimulation of the 
cell division of the “ germ-centres ” of lymphoid organs preceded 
lymphocytosis in the blood. The germ-centres are the birthplaces of 
blood lymphocytes. J. A. T. 
Viscosity Changes during Mitosis. — L. V. Heilbrunn ( Joum . 
Exper. Zool ., 1921, 34, 417-47, 1 chart). The velocity of granular 
movement under the influence of centrifugal force was taken as a 
measure of viscosity, and the viscosity of the cytoplasm of the egg of 
Gumingia was determined between fertilization and the first cleavage. 
In both maturation divisions and cleavage, appearance of the spindle 
is always preceded by a sharp viscosity increase and followed by a sharp 
viscosity decrease. At the conclusion of mitosis, within a minute or two 
before the division of the cell is completed, a sharp increase in viscosity 
occurs. When two mitoses follow each other, the concluding viscosity 
increase of the first mitosis becomes the initial viscosity increase of the 
second. There are similar changes in the egg of Nereis , but less 
marked, this being correlated with the larger size of the Nereis egg 
and the relatively small size of its spindle. J. A. T. 
Structure of Hypophysis in Urodela.— Wayne J. Atwell {Anat. 
Record , 1921, 22, 373-90, 19 figs.). In tailed amphibians ( Amblystoma , 
Necturus , Spelerpes, Amphiuma) the epithelial hypophysis is developed 
from the ectoderm, and differentiates into three lobes : the pars anterior 
proprior, the pars intermedia, and the pars tuberalis. The pars anterior 
proprior, or anterior lobe proper, forms the main bulk of the gland and 
comes to be caudal and ventral to the infundibulum. The pars inter- 
media is developed from the dorso-caudal extremity of the early 
hypophysial primordium. In its adult position it lies caudal to the 
neural lobe and dorsal to the anterior lobe. The pars tuberalis develops 
from a pair of processes which grow forward from the remainder of the 
gland. These processes do not become detached to form separate epi- 
thelial plaques as in the Anura, but maintain their connexions with the 
anterior lobe throughout life. The neural lobe is considerably saccu- 
lated in Necturus and Amphiuma , and this would of itself suggest that 
these two forms are primitive, and rather closely related to certain of 
the fishes. J. A. T. 
