ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
159 
may be arranged in an ascending series proceeding from the undifferen- 
tiated to the differentiated. 
Experimental Embryology.* — Prof. 0. Schultze has experimented 
as to the influence of cold on the development of the frog. He finds 
that after three days at zero, during which development was quite 
inhibited, there was not the least injurious effect observable. In the case 
of others kept fourteen days in the same conditions, those which had 
reached the stage with closed medullary canal perished, but all the rest, 
on to the stage of completed gastrulation, were unaffected. While 
Hertwig found twenty-four hours of zero temperature to be productive 
of injury to the ova, Schultze got normal embryos after twenty days. 
Prof. Schultze j has also experimented as to the influence of gravity 
on the developing ova of frogs. He has repeated and confirmed some 
of Pfliiger’s well-known experiments. Pfliiger showed that the first 
two cleavages were always vertical, whatever the angle (normally nil) 
between the egg-axis and the direction of gravity ; that the rapidity 
of cell-division is dependent on the action of gravity ; and that gravity 
influences the disposition of the organs. These .results have been con- 
firmed by zoologists, e. g. Rauber, Born, and the author, and also by 
botanists. 
To keep the ova in an abnormal position, Schultze compressed them 
between horizontal glass plates. Eggs thus inverted showed equal 
segmentation and other peculiarities. The degree of abnormality is 
proportional to the angle between the normal egg -axis and the direction 
of gravity. With great regularity a simple turning of the fixed ovum 
through 180° is followed by the production of a double embryo, and 
the author justly expands on this interesting result, and on analogous 
phenomena. Occasionally the double larvae reached the swimming 
stage, with double brain, spinal chord, and notochord. 
We need not summarize Schultze’s clear criticism of Roux’s disap- 
preciation of Pfliiger’s results, nor explain his machine for subjecting 
ova to rotation (at once fatal if on a vertical plane) ; his general argu- 
ment is, that if definite modifications in the action of gravity produce 
definite abnormalities, then it must be allowed that the action of gravity 
is a condition of normal development. 
B. Histology. 
Cell-structure.J — Herr Gr. Schloter describes in the cells of the 
Salamander (1) a coarse nuclear framework with “ nuclear sap ” in the 
interstices ; (2) the granulation of the framework, some of the granules 
being, probably, plasmosomes; (3) the granulation of the “nuclear 
sap” or paralinin with achromatin granules. The. author agrees both 
with Heidenhain and Reinke, and adds Altmann’s granula to the 
“ oxy chromatin,” “ oedematin,” &c., which are now described. The 
achromatin-granulation is Altmann’s granulation, “ oxychromatin ” and 
“ cyanophilous granulation ” are independent structural parts of the 
chromatin framework. Reinke has, though he may not think so, left 
out Heidenhain’s oxychromatin ; and Heidenhain has left out Reinke’s 
* Anat. Anzeig., x. (1894) pp. 291-4. 
+ Verb. Phys. Med. Ges. Wurzburg, xxviii. (1894) pp. 23-44. 
% Archiv f. Mikr. Anat., xliv. (1894) pp. 249-59 (1 pi.). 
