1896.] Embryology. 1059 
EMBRYOLOGY! 
Movements of Blastomeres.—In a copiously illustrated and 
extensive paper on the cleavage of Ascaris megalocephala Otto zur 
Strassen’ lays special emphasis upon certain movements of the cells of 
the embryo. 
In the living egg most remarkable rearrangements of the material 
are easily seen when the first four cells glide over one another. In later 
stages changes in form are traced to movements of the cells that must 
have taken place though not actually seen but inferred from a very 
detailed study of preserved material. The author confined his atten- 
tion chiefly to the ectodermal layer of cells and knowing the pedigree 
of a very large number of them was able to affirm that the changes in 
shape that the embryo exhibits are due, in part at least, to an actual 
migration or rearrangement of cells. Cell division and surface tension 
are not the only factors concerned in this change of position of the 
cells; there must be some individual movement of certain cells. 
This movement of the cells is regarded as being of the same nature as 
that observed by Roux in the isolated cells of the frog’s egg and is, 
therefore, designated Cytotropism. 
he production of form in the development of the Ascaris embryo 
has then this important factor—a power of cells to move towards one 
another and thus change the shape of the entire mass. This movement 
is in addition to any purely mechanical movements due to surface ten- 
sion and is due either to attraction between cells or to repulsion between 
cells. In either case it is assumed that chemical influences are at work : 
that this movement arises from chemotactic strains. 
The movements are much restricted in that a cell travels its own 
length at most and is never free from its sister-cell. In fact the two 
cells that arise from the division of one remain connected and are not 
to be separated by any intrusion of migrating cells and the author 
thinks that the movements are probably even more restricted in being 
merely the rearrangements of two groups of such sister-cells both 
derived from one parent, being merely readjustments of four grand- 
children of one cell! The entire ectoderm may then be regarded as a 
mosaié of such sets of families of four, each having its own internal 
readjustments. 
i Edited by E. ` Andrews, Baltimore, Md., to whom abstracts reviews and 
preliminary notes sent. 
ries 3 aroteorio aik; 3, 1896, pps. 27-101, 133--188, Pls. V--IX. 
