ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
461 
author’s opinion, the mechanical result of contraction. It is the ex- 
pression of the fact that in very active muscles stronger and weaker 
waves follow one another alternately. Everything tends to confirm the 
view of Kolliker that the alternation of darker and clearer parts is due 
to differences in the aggregation of the parts of one and the same mass ; 
this mass must have the nature of a viscous fluid. The author is 
opposed to the view that the intermediate discs are comparatively firmly 
fixed partitions. 
It appears that the contractions of the plasma constantly take place 
in a definite direction, and the peculiar property of the muscular mass 
consists in this, that the contractions of a body or of its parts are effected 
in definite directions. It is undoubted that from the primitively homo- 
geneous foundation from which muscular and connective tissue are 
developed in multicellular animals, muscular tissue is developed along 
the lines in which especially active contraction is effected, while con- 
nective tissue becomes developed in the non-active parts. Muscular 
masses almost always first appear in the outer layer of active parts ; in 
unicellular animals it is formed from the outer plasmatic layer of the 
body ; in multicellular forms it appears first in the dermo-muscular 
layer. These and other facts show that mechanical work is the cause of the 
form taken by the tissue. Each muscular filament is to be regarded as 
a column of the muscular mass which has become what it is in con- 
sequence of continued contractions in a direction perpendicular to its 
primitive surface. Cross-striation is the expression of constant waves 
in the muscular mass formed under nervous influence. 
Present State of the Doctrine of Cell-division.* — Dr. R. Zander 
sums up, in a very useful way, the present state of the doctrine of cell- 
division. Advances have no doubt been made, but the author points 
out that we are still far from being able to make a final judgment. A 
bibliography of 94 papers is appended. 
Leucoblasts and Erythroblasts.j — Prof. M. Lowit pursues his 
researches on the two kinds of haematopoetic elements — leucoblasts and 
erythroblasts — which he distinguishes in blood-forming organs. His 
present inquiry concerns the arrangement and formation of these 
elements in the organs. He has succeeded in technically differentiating 
the two kinds by the use of platinum chloride. The erythroblasts are 
distinguished by their nuclein or chromatin ; the leucoblasts by their 
nucleolin or pyrenin. 
He first describes the fixed cells in the blood-forming organs. 
These are connective-tissue cells and elements of endothelial or epithelial 
character. Lowit finds no support for the view that the leucocytes arise 
from the mitosis of endothelial cells. He then describes the erythro- 
blasts, the colourless elements which give rise to red blood-corpuscles. 
They occur in lymph-glands, spleen, medulla, single and grouped 
follicles of the intestine, and in the embryonic liver. They always 
exhibit the same definite nuclear peculiarities which the author describes 
at length. They multiply exclusively by mitosis, and do not arise from 
fixed tissue-elements. On the contrary they are distinct from the 
* Biol. Centralbl., xii. (1892) pp. 281-309. 
f Arch. f. Mikr. Anat., xxxviii. (1891) pp. 524—612 (3 pis.). 
