1897.] Hammar’s Ectoplasmie Layer. 1027 
HAMMAR’S ECTOPLASMIC LAYER. 
By E. A. ANDREWS. 
Twenty years ago Selenka observed and figured a connection 
between the outer parts of the cells in cleaving eggs of 
several Echinoderms, but it remained for Professor Hammar 
to point out, in 1895,' the great significance of this intercellu- 
lar structure. 
In the sea urchin, Echinus miliaris, he found a thin outer 
coat that did not take part in cleavage, but remained as a con- 
tinuous envelope over all the cells. This he interpreted as an 
ectoplasmie part of the egg, as a living connection between the 
cells, and as such of greatest import in understanding the in- 
teractions of cells in cleavage and in throwing light upon the 
divergent results of recent experimental work upon cleaving 
eggs. This, he thought, might be that organic intercellular 
connection potulated as = by Whitman, es and 
others. 
Proof, however, of the living nature of this ie seems 
wanting ; the figures of preserved sections raise a question as 
to how far the result may be due to or affected by the reagent 
used; and that the layer has a structure somewhat like an 
alveolar layer of Biitschli indicates, but does not prove, that 
the layer was actually living substance. 
Later, E. B. Wilson? stated that he had, in the main, verified 
Hammar’ s results upon sea urchin eggs, presumably upon pre- 
served material also. 
The same objection may be raised against accepting all the 
results -stibsequently obtained by Hammar,’ for though he 
found the outer ends of the cleaving cells of the eggs in Coelente- 
rates, Annelids, Molluses, Arthropods and Tunicates connected 
by a thin line of substance, and though a similar connection is 
shown in the epithelium of peye vertebrate embryos, yet the 
1 Archiv. f. Mik. Anat., V, 47. 
2 The Cell, p. 43. Macmillan Co.. N. Y. 
SArchiv.-f. Mik. Anat., 49: — 
